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Discussion 8 Part 1

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Read “Mirror neurons and their function in cognitively understood Empathy” , and then discuss, in general terms, what the mirror neurons system is (using the article as a primary source). Are there certain parts of the brain that have a higher number of these cells? Also consider how plasticity relates to this. In other words, is it possible that mirror neurons are the product of the environment to a certain extent? Support your responses.

Discussion 8 Part 2

Read “THE MIRROR-NEURON SYSTEM”, and then discuss the purpose, general methods, main results, and significance of the studies. Considering the function of empathy from the perspective of a cognitive neuroscientist, what adaptive functions could empathy serve? Also, consider the implications of lacking empathy.

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Annu. Rev. Neurosci. 2004. 27:169–92 doi: 10.1146/annurev.neuro.27.070203.144230

Copyright c© 2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on March 5, 2004

THE MIRROR-NEURON SYSTEM

Giacomo Rizzolatti1 and Laila Craighero2 1Dipartimento di Neuroscienze, Sezione di Fisiologia, via Volturno, 3, Università di Parma, 43100, Parma, Italy; email: [email protected]; 2Dipartimento SBTA, Sezione di Fisiologia Umana, via Fossato di Mortara, 17/19, Università di Ferrara, 44100 Ferrara, Italy; email: [email protected]

Key Words mirror neurons, action understanding, imitation, language, motor cognition

� Abstract A category of stimuli of great importance for primates, humans in particular, is that formed by actions done by other individuals. If we want to survive, we must understand the actions of others. Furthermore, without action understanding, social organization is impossible. In the case of humans, there is another faculty that depends on the observation of others’ actions: imitation learning. Unlike most species, we are able to learn by imitation, and this faculty is at the basis of human culture. In this review we present data on a neurophysiological mechanism—the mirror-neuron mechanism—that appears to play a fundamental role in both action understanding and imitation. We describe first the functional properties of mirror neurons in monkeys. We review next the characteristics of the mirror-neuron system in humans. We stress, in particular, those properties specific to the human mirror-neuron system that might explain the human capacity to learn by imitation. We conclude by discussing the relationship between the mirror-neuron system and language.

INTRODUCTION

Mirror neurons are a particular class of visuomotor neurons, originally discovered in area F5 of the monkey premotor cortex, that discharge both when the monkey does a particular action and when it observes another individual (monkey or human) doing a similar action (Di Pellegrino et al. 1992, Gallese et al. 1996, Rizzolatti et al. 1996a). A lateral view of the monkey brain showing the location of area F5 is presented in Figure 1.

The aim of this review is to provide an updated account of the functional properties of the system formed by mirror neurons. The review is divided into four sections. In the first section we present the basic functional properties of mirror neurons in the monkey, and we discuss their functional roles in action understanding. In the second section, we present evidence that a mirror-neuron system similar to that of the monkey exists in humans. The third section shows that in humans, in addition to action understanding, the mirror-neuron system plays a fundamental role in action imitation. The last section is more speculative.

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We present there a theory of language evolution, and we discuss a series of data supporting the notion of a strict link between language and the mirror-neuron system (Rizzolatti & Arbib 1998).

THE MIRROR-NEURON SYSTEM IN MONKEYS

F5 Mirror Neurons: Basic Properties

There are two classes of visuomotor neurons in monkey area F5: canonical neurons, which respond to the presentation of an object, and mirror neurons, which respond when the monkey sees object-directed action (Rizzolatti & Luppino 2001). In order to be triggered by visual stimuli, mirror neurons require an interaction between a biological effector (hand or mouth) and an object. The sight of an object alone, of an agent mimicking an action, or of an individual making intransitive (nonobject- directed) gestures are all ineffective. The object significance for the monkey has no obvious influence on the mirror-neuron response. Grasping a piece of food or a geometric solid produces responses of the same intensity.

Mirror neurons show a large degree of generalization. Presenting widely differ- ent visual stimuli, but which all represent the same action, is equally effective. For example, the same grasping mirror neuron that responds to a human hand grasping an object responds also when the grasping hand is that of a monkey. Similarly, the response is typically not affected if the action is done near or far from the monkey, in spite of the fact that the size of the observed hand is obviously different in the two conditions.

It is also of little importance for neuron activation if the observed action is even- tually rewarded. The discharge is of the same intensity if the experimenter grasps the food and gives it to the recorded monkey or to another monkey introduced in the experimental room.

An important functional aspect of mirror neurons is the relation between their visual and motor properties. Virtually all mirror neurons show congruence between the visual actions they respond to and the motor responses they code. According to the type of congruence they exhibit, mirror neurons have been subdivided into “strictly congruent” and “broadly congruent” neurons (Gallese et al. 1996).

Mirror neurons in which the effective observed and effective executed actions correspond in terms of goal (e.g., grasping) and means for reaching the goal (e.g., precision grip) have been classed as “strictly congruent.” They represent about one third of F5 mirror neurons. Mirror neurons that, in order to be triggered, do not require the observation of exactly the same action that they code motorically have been classed as “broadly congruent.” They represent about two thirds of F5 mirror neurons.

F5 Mouth Mirror Neurons

The early studies of mirror neurons concerned essentially the upper sector of F5 where hand actions are mostly represented. Recently, a study was carried out on

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the properties of neurons located in the lateral part of F5 (Ferrari et al. 2003), where, in contrast, most neurons are related to mouth actions.

The results showed that about 25% of studied neurons have mirror properties. According to the visual stimuli effective in triggering the neurons, two classes of mouth mirror neurons were distinguished: ingestive and communicative mirror neurons.

Ingestive mirror neurons respond to the observation of actions related to in- gestive functions, such as grasping food with the mouth, breaking it, or sucking. Neurons of this class form about 80% of the total amount of the recorded mouth mirror neurons. Virtually all ingestive mirror neurons show a good correspondence between the effective observed and the effective executed action. In about one third of them, the effective observed and executed actions are virtually identical (strictly congruent neurons); in the remaining, the effective observed and executed actions are similar or functionally related (broadly congruent neurons).

More intriguing are the properties of the communicative mirror neurons. The most effective observed action for them is a communicative gesture such as lip smacking, for example. However, from a motor point of view they behave as the ingestive mirror neurons, strongly discharging when the monkey actively performs an ingestive action.

This discrepancy between the effective visual input (communicative) and the effective active action (ingestive) is rather puzzling. Yet, there is evidence suggest- ing that communicative gestures, or at least some of them, derived from ingestive actions in evolution (MacNeilage 1998, Van Hoof 1967). From this perspective one may argue that the communicative mouth mirror neurons found in F5 reflect a process of corticalization of communicative functions not yet freed from their original ingestive basis.

The Mirror-Neuron Circuit

Neurons responding to the observation of actions done by others are present not only in area F5. A region in which neurons with these properties have been de- scribed is the cortex of the superior temporal sulcus (STS; Figure 1) (Perrett et al. 1989, 1990; Jellema et al. 2000; see Jellema et al. 2002). Movements effective in eliciting neuron responses in this region are walking, turning the head, bending the torso, and moving the arms. A small set of STS neurons discharge also during the observation of goal-directed hand movements (Perrett et al. 1990).

If one compares the functional properties of STS and F5 neurons, two points emerge. First, STS appears to code a much larger number of movements than F5. This may be ascribed, however, to the fact that STS output reaches, albeit indirectly (see below), the whole ventral premotor region and not only F5. Second, STS neurons do not appear to be endowed with motor properties.

Another cortical area where there are neurons that respond to the observation of actions done by other individuals is area 7b or PF of Von Economo (1929) (Fogassi et al. 1998, Gallese et al. 2002). This area (see Figure 1) forms the rostral part of the

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inferior parietal lobule. It receives input from STS and sends an important output to the ventral premotor cortex including area F5.

PF neurons are functionally heterogeneous. Most of them (about 90%) respond to sensory stimuli, but about 50% of them also have motor properties discharging when the monkey performs specific movements or actions (Fogassi et al. 1998, Gallese et al. 2002, Hyvarinen 1982).

PF neurons responding to sensory stimuli have been subdivided into “so- matosensory neurons” (33%), “visual neurons” (11%), and “bimodal (somatosen- sory and visual) neurons” (56%). About 40% of the visually responsive neurons respond specifically to action observation and of them about two thirds have mirror properties (Gallese et al. 2002).

In conclusion, the cortical mirror neuron circuit is formed by two main regions: the rostral part of the inferior parietal lobule and the ventral premotor cortex. STS is strictly related to it but, lacking motor properties, cannot be considered part of it.

Function of the Mirror Neuron in the Monkey: Action Understanding

Two main hypotheses have been advanced on what might be the functional role of mirror neurons. The first is that mirror-neuron activity mediates imitation (see Jeannerod 1994); the second is that mirror neurons are at the basis of action understanding (see Rizzolatti et al. 2001).

Both these hypotheses are most likely correct. However, two points should be specified. First, although we are fully convinced (for evidence see next section) that the mirror neuron mechanism is a mechanism of great evolutionary importance through which primates understand actions done by their conspecifics, we cannot claim that this is the only mechanism through which actions done by others may be understood (see Rizzolatti et al. 2001). Second, as is shown below, the mirror- neuron system is the system at the basis of imitation in humans. Although laymen are often convinced that imitation is a very primitive cognitive function, they are wrong. There is vast agreement among ethologists that imitation, the capacity to learn to do an action from seeing it done (Thorndyke 1898), is present among primates, only in humans, and (probably) in apes (see Byrne 1995, Galef 1988, Tomasello & Call 1997, Visalberghi & Fragaszy 2001, Whiten & Ham 1992). Therefore, the primary function of mirror neurons cannot be action imitation.

How do mirror neurons mediate understanding of actions done by others? The proposed mechanism is rather simple. Each time an individual sees an action done by another individual, neurons that represent that action are activated in the observer’s premotor cortex. This automatically induced, motor representation of the observed action corresponds to that which is spontaneously generated during active action and whose outcome is known to the acting individual. Thus, the mirror system transforms visual information into knowledge (see Rizzolatti et al. 2001).

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Evidence in Favor of the Mirror Mechanism in Action Understanding

At first glance, the simplest, and most direct, way to prove that the mirror-neuron system underlies action understanding is to destroy it and examine the lesion effect on the monkey’s capacity to recognize actions made by other monkeys. In practice, this is not so. First, the mirror-neuron system is bilateral and includes, as shown above, large portions of the parietal and premotor cortex. Second, there are other mechanisms that may mediate action recognition (see Rizzolatti et al. 2001). Third, vast lesions as those required to destroy the mirror neuron system may produce more general cognitive deficits that would render difficult the interpretation of the results.

An alternative way to test the hypothesis that mirror neurons play a role in action understanding is to assess the activity of mirror neurons in conditions in which the monkey understands the meaning of the occurring action but has no access to the visual features that activate mirror neurons. If mirror neurons mediate action understanding, their activity should reflect the meaning of the observed action, not its visual features.

Prompted by these considerations, two series of experiments were carried out. The first tested whether F5 mirror neurons are able to recognize actions from their sound (Kohler et al. 2002), the second whether the mental representation of an action triggers their activity (Umiltà et al. 2001).

Kohler et al. (2002) recorded F5 mirror neuron activity while the monkey was observing a noisy action (e.g., ripping a piece of paper) or was presented with the same noise without seeing it. The results showed that about 15% of mirror neurons responsive to presentation of actions accompanied by sounds also responded to the presentation of the sound alone. The response to action sounds did not depend on unspecific factors such as arousal or emotional content of the stimuli. Neurons re- sponding specifically to action sounds were dubbed “audio-visual” mirror neurons.

Neurons were also tested in an experimental design in which two noisy actions were randomly presented in vision-and-sound, sound-only, vision-only, and motor conditions. In the motor condition, the monkeys performed the object-directed action that they observed or heard in the sensory conditions. Out of 33 studied neurons, 29 showed auditory selectivity for one of the two hand actions. The selectivity in visual and auditory modality was the same and matched the preferred motor action.

The rationale of the experiment by Umiltà et al. (2001) was the following. If mirror neurons are involved in action understanding, they should discharge also in conditions in which monkey does not see the occurring action but has sufficient clues to create a mental representation of what the experimenter does. The neurons were tested in two basic conditions. In one, the monkey was shown a fully visible action directed toward an object (“full vision” condition). In the other, the monkey saw the same action but with its final, critical part hidden (“hidden” condition). Before each trial, the experimenter placed a piece of food behind the screen so

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that the monkey knew there was an object there. Only those mirror neurons were studied that discharged to the observation of the final part of a grasping movement and/or to holding.

Figure 2 shows the main result of the experiment. The neuron illustrated in the figure responded to the observation of grasping and holding (A, full vision). The neuron discharged also when the stimulus-triggering features (a hand approaching the stimulus and subsequently holding it) were hidden from monkey’s vision (B, hidden condition). As is the case for most mirror neurons, the observation of a mimed action did not activate the neuron (C, full vision, and D, hidden condition). Note that from a physical point of view B and D are identical. It was therefore the understanding of the meaning of the observed actions that determined the discharge in the hidden condition.

More than half of the tested neurons discharged in the hidden condition. Out of them, about half did not show any difference in the response strength between the hidden- and full-vision conditions. The other half responded more strongly in the full-vision condition. One neuron showed a more pronounced response in the hidden condition than in full vision.

In conclusion, both the experiments showed that the activity of mirror neurons correlates with action understanding. The visual features of the observed actions are fundamental to trigger mirror neurons only insomuch as they allow the under- standing of the observed actions. If action comprehension is possible on another basis (e.g., action sound), mirror neurons signal the action, even in the absence of visual stimuli.

THE MIRROR-NEURON SYSTEM IN HUMANS

There are no studies in which single neurons were recorded from the putative mirror-neuron areas in humans. Thus, direct evidence for the existence of mirror neurons in humans is lacking. There is, however, a rich amount of data proving, indirectly, that a mirror-neuron system does exist in humans. Evidence of this comes from neurophysiological and brain-imaging experiments.

Neurophysiological Evidence

Neurophysiological experiments demonstrate that when individuals observe an action done by another individual their motor cortex becomes active, in the absence of any overt motor activity. A first evidence in this sense was already provided in the 1950s by Gastaut and his coworkers (Cohen-Seat et al. 1954, Gastaut & Bert 1954). They observed that the desynchronization of an EEG rhythm recorded from central derivations (the so-called mu rhythm) occurs not only during active movements of studied subjects, but also when the subjects observed actions done by others.

This observation was confirmed by Cochin et al. (1998, 1999) and by Altschuler et al. (1997, 2000) using EEG recordings, and by Hari et al. (1998) using

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magnetoencephalographic (MEG) technique. This last study showed that the desyn- chronization during action observation includes rhythms originating from the cor- tex inside the central sulcus (Hari & Salmelin 1997, Salmelin & Hari 1994).

More direct evidence that the motor system in humans has mirror properties was provided by transcranial magnetic stimulation (TMS) studies. TMS is a non- invasive technique for electrical stimulation of the nervous system. When TMS is applied to the motor cortex, at appropriate stimulation intensity, motor-evoked potentials (MEPs) can be recorded from contralateral extremity muscles. The am- plitude of these potentials is modulated by the behavioral context. The modu- lation of MEPs’ amplitude can be used to assess the central effects of various experimental conditions. This approach has been used to study the mirror neuron system.

Fadiga et al. (1995) recorded MEPs, elicited by stimulation of the left motor cortex, from the right hand and arm muscles in volunteers required to observe an experimenter grasping objects (transitive hand actions) or performing meaningless arm gestures (intransitive arm movements). Detection of the dimming of a small spot of light and presentation of 3-D objects were used as control conditions. The results showed that the observation of both transitive and intransitive actions determined an increase of the recorded MEPs with respect to the control conditions. The increase concerned selectively those muscles that the participants use for producing the observed movements.

Facilitation of the MEPs during movement observation may result from a fa- cilitation of the primary motor cortex owing to mirror activity of the premotor areas, to a direct facilitatory input to the spinal cord originating from the same areas, or from both. Support for the cortical hypothesis (see also below, Brain Imaging Experiments) came from a study by Strafella & Paus (2000). By using a double-pulse TMS technique, they demonstrated that the duration of intracortical recurrent inhibition, occurring during action observation, closely corresponds to that occurring during action execution.

Does the observation of actions done by others influence the spinal cord ex- citability? Baldissera et al. (2001) investigated this issue by measuring the size of the H-reflex evoked in the flexor and extensor muscles of normal volunteers during the observation of hand opening and closure done by another individual. The results showed that the size of H-reflex recorded from the flexors increased during the observation of hand opening, while it was depressed during the ob- servation of hand closing. The converse was found in the extensors. Thus, while the cortical excitability varies in accordance with the seen movements, the spinal cord excitability changes in the opposite direction. These findings indicate that, in the spinal cord, there is an inhibitory mechanism that prevents the execution of an observed action, thus leaving the cortical motor system free to “react” to that action without the risk of overt movement generation.

In a study of the effect of hand orientation on cortical excitability, Maeda et al. (2002) confirmed (see Fadiga et al. 1995) the important finding that, in humans, intransitive movements, and not only goal-directed actions, determine

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motor resonance. Another important property of the human mirror-neuron system, demonstrated with TMS technique, is that the time course of cortical facilitation during action observation follows that of movement execution. Gangitano et al. (2001) recorded MEPs from the hand muscles of normal volunteers while they were observing grasping movements made by another individual. The MEPs were recorded at different intervals following the movement onset. The results showed that the motor cortical excitability faithfully followed the grasping movement phases of the observed action.

In conclusion, TMS studies indicate that a mirror-neuron system (a motor res- onance system) exists in humans and that it possesses important properties not observed in monkeys. First, intransitive meaningless movements produce mirror- neuron system activation in humans (Fadiga et al. 1995, Maeda et al. 2002, Patuzzo et al. 2003), whereas they do not activate mirror neurons in monkeys. Second, the temporal characteristics of cortical excitability, during action observation, suggest that human mirror-neuron systems code also for the movements forming an action and not only for action as monkey mirror-neuron systems do. These properties of the human mirror-neuron system should play an important role in determining the humans’ capacity to imitate others’ action.

Brain Imaging Studies: The Anatomy of the Mirror System

A large number of studies showed that the observation of actions done by others activates in humans a complex network formed by occipital, temporal, and parietal visual areas, and two cortical regions whose function is fundamentally or predom- inantly motor (e.g., Buccino et al. 2001; Decety et al. 2002; Grafton et al. 1996; Grèzes et al. 1998; Grèzes et al. 2001; Grèzes et al. 2003; Iacoboni et al. 1999, 2001; Koski et al. 2002, 2003; Manthey et al. 2003; Nishitani & Hari 2000, 2002; Perani et al. 2001; Rizzolatti et al. 1996b). These two last regions are the rostral part of the inferior parietal lobule and the lower part of the precentral gyrus plus the posterior part of the inferior frontal gyrus (IFG). These regions form the core of the human mirror-neuron system.

Which are the cytoarchitectonic areas that form these regions? Interpretation of the brain-imaging activations in cytoarchitectonic terms is always risky. Yet, in the case of the inferior parietal region, it is very plausible that the mirror activation corresponds to areas PF and PFG, where neurons with mirror properties are found in the monkeys (see above).

More complex is the situation for the frontal regions. A first issue concerns the location of the border between the two main sectors of the premotor cortex: the ventral premotor cortex (PMv) and the dorsal premotor cortex (PMd). In nonhuman primates the two sectors differ anatomically (Petrides & Pandya 1984, Tanné- Gariepy et al. 2002) and functionally (see Rizzolatti et al. 1998). Of them, PMv only has (direct or indirect) anatomical connections with the areas where there is visual coding of action made by others (PF/PFG and indirectly STS) and, thus, where there is the necessary information for the formation of mirror neurons (Rizzolatti & Matelli 2003).

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On the basis of embryological considerations, the border between human PMd and PMv should be located, approximately, at Z level 50 in Talairach coordinates (Rizzolatti & Arbib 1998, Rizzolatti et al. 2002). This location derives from the view that the superior frontal sulcus (plus the superior precentral sulcus) represents the human homologue of the superior branch of the monkey arcuate sulcus. Because the border of monkey PMv and PMd corresponds approximately to the caudal continuation of this branch, the analogous border should, in humans, lie slightly ventral to the superior frontal sulcus.

The location of human frontal eye field (FEF) supports this hypothesis (Corbetta 1998, Kimming et al. 2001, Paus 1996, Petit et al.1996). In monkeys, FEF lies in the anterior bank of the arcuate sulcus, bordering posteriorly the sector of PMv where arm and head movements are represented (area F4). If one accepts the location of the border between PMv and PMd suggested above, FEF is located in a similar position in the two species. In both of them, the location is just anterior to the upper part of PMv and the lowest part of PMd.

The other issue concerns IFG areas. There is a deeply rooted prejudice that these areas are radically different from those of the precentral gyrus and that they are exclusively related to speech (e.g., Grèzes & Decety 2001). This is not so. Already at the beginning of the last century, Campbell (1905) noted clear anatomical simi- larities between the areas of posterior IFG and those of the precentral gyrus. This author classed both the pars opercularis and the pars triangularis of IFG together with the precentral areas and referred to them collectively as the “intermediate pre- central” cortex. Modern comparative studies indicate that the pars opercularis of IFG (basically corresponding to area 44) is the human homologue of area F5 (Von Bonin & Bailey 1947, Petrides & Pandya 1997). Furthermore, from a functional perspective, clear evidence has been accumulating in recent years that human area 44, in addition to speech representation, contains (as does monkey area F5) a mo- tor representation of hand movements (Binkofski et al. 1999, Ehrsson et al. 2000, Gerardin et al. 2000, Iacoboni et al. 1999, Krams et al. 1998). Taken together, these data strongly suggest that human PMv is the homologue of monkey area F4, and human area 44 is the homologue of monkey area F5. The descending branch of the inferior precentral sulcus (homologue to the monkey inferior precentral dimple) should form the approximate border between the two areas (for individual vari- ations of location and extension area 44, see Amunts et al. 1999 and Tomaiuolo et al. 1999).

If the homology just described is correct, one should expect that the observation of neck and proximal arm movements would activate predominantly PMv, whereas hand and mouth movements would activate area 44. Buccino et al. (2001) addressed this issue in an fMRI experiment. Normal volunteers were presented with video clips showing actions performed with the mouth, hand/arm, and foot/leg. Both transitive (actions directed toward an object) and intransitive actions were shown. Action observation was contrasted with the observation of a static face, hand, and foot (frozen pictures of the video clips), respectively.

Observation of object-related mouth movements determined activation of the lower part of the precentral gyrus and of the pars opercularis of the inferior frontal

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gyrus (IFG), bilaterally. In addition, two activation foci were found in the parietal lobe. One was located in the rostral part of the inferior parietal lobule (most likely area PF), whereas the other was located in the posterior part of the same lobule. The observation of intransitive actions activated the same premotor areas, but there was no parietal lobe activation.

Observation of object-related hand/arm movements determined two areas of activation in the frontal lobe, one corresponding to the pars opercularis of IFG and the other located in the precentral gyrus. The latter activation was more dorsally located than that found during the observation of mouth movements. As for mouth movements, there were two activation foci in the parietal lobe. The rostral focus was, as in the case of mouth actions, in the rostral part of the inferior parietal lobule, but more posteriorly located, whereas the caudal focus was essentially in the same location as that for mouth actions. During the observation of intransitive movements the premotor activations were present, but the parietal ones were not.

Finally, the observation of object-related foot/leg actions determined an acti- vation of a dorsal sector of the precentral gyrus and an activation of the posterior parietal lobe, in part overlapping with those seen during mouth and hand actions, in part extending more dorsally. Intransitive foot actions produced premotor, but not parietal, activation.

A weakness of the data by Buccino et al. (2001) is that they come from a group study. Data from single individuals are badly needed for a more precise somatotopic map. Yet, they clearly show that both the frontal and the parietal “mirror” regions are somatotopically organized. The somatotopy found in the inferior parietal lobule is the same as that found in the monkey. As far as the frontal lobe is concerned, the data appear to confirm the predictions based on the proposed homology. The activation of the pars opercularis of IFG should reflect the observation of distal hand actions and mouth actions, whereas that of the precentral cortex activation should reflect that of proximal arm actions and of neck movements.

It is important to note that the observation of transitive actions activated both the parietal and the frontal node of the mirror-neuron system, whereas the intransitive actions activated the frontal node only. This observation is in accord with the lack of inferior parietal lobule activation found in other studies in which intransitive actions were used (e.g., finger movements; Iacoboni et al. 1999, 2001; Koski et al. 2002, 2003). Considering that the premotor areas receive visual information from the inferior parietal lobule, it is hard to believe that the inferior parietal lobule was not activated during the observation of intransitive actions. It is more likely, therefore, that when an object is present, the inferior parietal activation is stronger than when the object is lacking, and the activation, in the latter case, does not reach statistical significance.

Brain Imaging Studies: Mirror-Neuron System Properties

As discussed above, the mirror-neuron system is involved in action understanding. An interesting issue is whether this is true also for actions done by individuals

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belonging to other species. Is the understanding by humans of actions done by monkeys based on the mirror-neuron system? And what about more distant species, like dogs?

Recently, an fMRI experiment addressed these questions (Buccino et al. 2004). Video clips showing silent mouth actions performed by humans, monkeys, and dogs were presented to normal volunteers. Two types of actions were shown: biting and oral communicative actions (speech reading, lip smacking, barking). As a control, static images of the same actions were presented.

The results showed that the observation of biting, regardless of whether it was performed by a man, a monkey, or a dog, determined the same two activation foci in the inferior parietal lobule discussed above and activation in the pars opercularis of the IFG and the adjacent precentral gyrus (Figure 3). The left rostral parietal focus and the left premotor focus were virtually identical for all three species, whereas the right side foci were stronger during the observation of actions made by a human being than by an individual of another species. Different results were obtained with communicative actions. Speech reading activated the left pars opercularis of IFG; observation of lip smacking, a monkey communicative gesture, activated a small focus in the right and left pars opercularis of IFG; observation of barking did not produce any frontal lobe activation (Figure 4).

These results indicated that actions made by other individuals could be recog- nized through different mechanisms. Actions belonging to the motor repertoire of the observer are mapped on his/her motor system. Actions that do not belong to this repertoire do not excite the motor system of the observer and appear to be recognized essentially on a visual basis without motor involvement. It is likely that these two different ways of recognizing actions have two different psychological counterparts. In the first case the motor “resonance” translates the visual experi- ence into an internal “personal knowledge“ (see Merleau-Ponty 1962), whereas this is lacking in the second case.

One may speculate that the absence of the activation of the frontal mirror area reported in some experiments might be due to the fact that the stimuli used (e.g., light point stimuli, Grèzes et al. 2001) were insufficient to elicit this “personal” knowledge of the observed action.

An interesting issue was addressed by Johnson Frey et al. (2003). Using event- related fMRI, they investigated whether the frontal mirror activation requires the observation of a dynamic action or if the understanding of the action goal is sufficient. Volunteers were presented with static pictures of the same objects be- ing grasped or touched. The results showed that the observation of the goals of hand-object interactions was sufficient to activate selectively the frontal mirror region.

In this experiment, pars triangularis of IFG has been found active in several subjects (see also Rizzolatti et al. 1996b, Grafton et al. 1996). In speech, this sector appears to be mostly related to syntax (Bookheimer 2002). Although one may be tempted to speculate that this area may code also the syntactic aspect of action (see Greenfield 1991), there is at present no experimental evidence in support of

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this proposal. Therefore, the presence of activation of pars triangularis lacks, at the moment, a clear explanation.

Schubotz & Von Cramon (2001, 2002a,b) tested whether the frontal mirror re- gion is important not only for the understanding of goal-directed actions, but also for recognizing predictable visual patterns of change. They used serial predic- tion tasks, which tested the participants’ performance in a sequential perceptual task without sequential motor responses. Results showed that serial prediction caused activation in premotor and parietal cortices, particularly within the right hemisphere. The authors interpreted these findings as supporting the notion that se- quential perceptual events can be represented independent of preparing an intended action toward the stimulus. According to these authors, the frontal mirror-neuron system node plays, in humans, a crucial role also in the representation of sequential information, regardless of whether it is perceptual or action related.

MIRROR-NEURON SYSTEM AND IMITATION

Imitation of Actions Present in the Observer’s Repertoire

Psychological experiments strongly suggest that, in the cognitive system, stimuli and responses are represented in a commensurable format (Brass et al. 2000, Craighero et al. 2002, Wohlschlager & Bekkering 2002; see Prinz 2002). When observers see a motor event that shares features with a similar motor event present in their motor repertoire, they are primed to repeat it. The greater the similarity between the observed event and the motor event, the stronger the priming is (Prinz 2002).

These findings, and the discovery of mirror neurons, prompted a series of ex- periments aimed at finding the neural substrate of this phenomenon (Iacoboni et al. 1999, 2001; Nishitani & Hari 2000, 2002).

Using fMRI, Iacoboni et al. (1999) studied normal human volunteers in two conditions: observation-only and observation-execution. In the “observation-only” condition, subjects were shown a moving finger, a cross on a stationary finger, or a cross on an empty background. The instruction was to observe the stimuli. In the “observation-execution” condition, the same stimuli were presented, but this time the instruction was to lift the right finger, as fast as possible, in response to them.

The most interesting statistical contrast was that between the trials in which the volunteers made the movement in response to an observed action (imitation) and the trials in which the movement was triggered by the cross. The results showed that the activity was stronger during imitation trials than during the other motor trials in four areas: the left pars opercularis of the IFG, the right anterior parietal region, the right parietal operculum, and the right STS region (see for this last activation Iacoboni et al. 2001). Further experiments by Koski et al. (2002) confirmed the importance of Broca’s area, in particular when the action to be imitated had a specific goal. Grèzes et al. (2003) obtained similar results, but only

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when participants had to imitate pantomimes. The imitation of object-directed actions surprisingly activated PMd.

Nishitani & Hari (2000, 2002) performed two studies in which they investigated imitation of grasping actions and of facial movements, respectively. The event- related MEG was used. The first study confirmed the importance of the left IFG (Broca’s area) in imitation. In the second study (Nishitani & Hari 2002), the authors asked volunteers to observe still pictures of verbal and nonverbal (grimaces) lip forms, to imitate them immediately after having seen them, or to make similar lip forms spontaneously. During lip form observation, cortical activation progressed from the occipital cortex to the superior temporal region, the inferior parietal lobule, IFG (Broca’s area), and finally to the primary motor cortex. The activation sequence during imitation of both verbal and nonverbal lip forms was the same as during observation. Instead, when the volunteers executed the lip forms spontaneously, only Broca’s area and the motor cortex were activated.

Taken together, these data clearly show that the basic circuit underlying im- itation coincides with that which is active during action observation. They also indicate that, in the posterior part of IFG, a direct mapping of the observed action and its motor representation takes place.

The studies of Iacoboni et al. (1999, 2001) showed also activations—superior parietal lobule, parietal operculum, and STS region—that most likely do not reflect a mirror mechanism. The activation of the superior parietal lobule is typically not present when subjects are instructed to observe actions without the instruction to imitate them (e.g., Buccino et al. 2001). Thus, a possible interpretation of this activation is that the request to imitate produces, through backward projections, sensory copies of the intended actions. In the monkey, superior parietal lobule and especially its rostral part (area PE) contains neurons that are active in response to proprioceptive stimuli as well as during active arm movements (Kalaska et al. 1983, Lacquaniti et al. 1995, Mountcastle et al. 1975). It is possible, therefore, that the observed superior parietal activation represents a kinesthetic copy of the intended movements. This interpretation fits well previous findings by Grèzes et al. (1998), who, in agreement with Iacoboni et al. (1999), showed a strong activation of superior parietal lobule when subjects’ tasks were to observe actions in order to repeat them later.

An explanation in terms of sensory copies of the intended actions may also account for the activations observed in the parietal operculum and STS. The first corresponds to the location of somatosensory areas hidden in the sylvian sulcus (Disbrow et al. 2000), whereas the other corresponds to higher-order visual areas of the STS region (see above). Thus, these two activations might reflect somatosen- sory and visual copies of the intended action, respectively.

The importance of the pars opercularis of IFG in imitation was further demon- strated using repetitive TMS (rTMS), a technique that transiently disrupts the functions of the stimulated area (Heiser et al. 2003). The task used in the study was, essentially, the same as that of Iacoboni et al. (1999). The results showed that following stimulation of both left and right Broca’s area, there was significant

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impairment in imitation of finger movements. The effect was absent when finger movements were done in response to spatial cues.

Imitation Learning

Broadly speaking, there are two types of newly acquired behaviors based on im- itation learning. One is substitution, for the motor pattern spontaneously used by the observer in response to a given stimulus, of another motor pattern that is more adequate to fulfill a given task. The second is the capacity to learn a motor sequence useful to achieve a specific goal (Rizzolatti 2004).

The neural basis of the capacity to form a new motor pattern on the basis of action observation was recently studied by Buccino et al. (G. Buccino, S. Vogt, A. Ritzl, G.R. Fink, K. Zilles, H.J. Freund & G. Rizzolatti, submitted manuscript), using an event-related fMRI paradigm. The basic task was the imitation, by naive participants, of guitar chords played by an expert guitarist. By using an event- related paradigm, cortical activation was mapped during the following events: (a) action observation, (b) pause (new motor pattern formation and consolidation), (c) chord execution, and (d) rest. In addition to imitation condition, there were three control conditions: observation without any motor request, observation followed by execution of a nonrelated action (e.g., scratching the guitar neck), and free execution of guitar chords.

The results showed that during the event observation-to-imitate there was ac- tivation of a cortical network that coincided with that which is active during observation-without-instruction-to-imitate and during observation in order not to imitate. The strength of the activation was, however, much stronger in the first con- dition. The areas forming this common network were the inferior parietal lobule, the dorsal part of PMv, and the pars opercularis of IFG. Furthermore, during the event observation-to-imitate, but not during observation-without-further-motor- action, there was activation of the superior parietal lobule, anterior mesial areas plus a modest activation of the middle frontal gyrus.

The activation during the pause event in imitation condition involved the same basic circuit as in event observation-of-the-same-condition, but with some impor- tant differences: increase of the superior parietal lobule activation, activation of PMd, and, most interestingly, a dramatic increase in extension and strength of the middle frontal cortex activation (area 46) and of the areas of the anterior mesial wall. Finally, during the execution event, not surprisingly, the activation concerned mostly the sensorimotor cortex contralateral to the acting hand.

These data show that the nodal centers for new motor pattern formation co- incide with the nodal mirror-neuron regions. Although fMRI experiments cannot give information on the mechanism involved, it is plausible (see the neurophys- iological sections) that during learning of new motor patterns by imitation the observed actions are decomposed into elementary motor acts that activate, via mirror mechanism, the corresponding motor representations in PF and in PMv and in the pars opercularis of IFG. Once these motor representations are activated,

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they are recombined, according to the observed model by the prefrontal cortex. This recombination occurs inside the mirror-neuron circuit with area 46 playing a fundamental orchestrating role.

To our knowledge, there are no brain-imaging experiments that studied the acquisition of new sequences by imitation from the perspective of mirror neurons. Theoretical aspect of sequential learning by imitation and its possible neural basis have been discussed by Arbib (2002), Byrne (2002), and Rizzolatti (2004). The interested reader can find there an exhaustive discussion of this issue.

MIRROR-NEURON SYSTEM AND COMMUNICATION

Gestural Communication

Mirror neurons represent the neural basis of a mechanism that creates a direct link between the sender of a message and its receiver. Thanks to this mechanism, actions done by other individuals become messages that are understood by an observer without any cognitive mediation.

On the basis of this property, Rizzolatti & Arbib (1998) proposed that the mirror- neuron system represents the neurophysiological mechanism from which language evolved. The theory of Rizzolatti & Arbib belongs to theories that postulate that speech evolved mostly from gestural communication (see Armstrong et al. 1995, Corballis 2002). Its novelty consists of the fact that it indicates a neurophysiological mechanism that creates a common (parity requirement), nonarbitrary, semantic link between communicating individuals.

The mirror-neuron system in monkeys is constituted of neurons coding object- directed actions. A first problem for the mirror-neuron theory of language evolution is to explain how this close, object-related system became an open system able to describe actions and objects without directly referring to them.

It is likely that the great leap from a closed system to a communicative mir- ror system depended upon the evolution of imitation (see Arbib 2002) and the related changes of the human mirror-neuron system: the capacity of mirror neu- rons to respond to pantomimes (Buccino et al. 2001, Grèzes et al. 2003) and to intransitive actions (Fadiga et al. 1995, Maeda et al. 2002) that was absent in monkeys.

The notion that communicative actions derived from object-directed actions is not new. Vygotski (1934), for example, explained that the evolution of pointing movements was due to attempts of children to grasp far objects. It is interesting to note that, although monkey mirror neurons do not discharge when the monkey observes an action that is not object directed, they do respond when an object is hidden, but the monkey knows that the action has a purpose (Kohler et al. 2002). This finding indicates that breaking spatial relations between effector and target does not impair the capacity of understanding the action meaning. The precondition for understanding pointing—the capacity to mentally represent the action goal—is already present in monkeys.

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A link between object-directed and communicative action was also stressed by other authors (see McNeilage 1998, Van Hoof 1967; for discussion of this link from the mirror neurons perspective, see above).

Mirror Neurons and Speech Evolution

The mirror neuron communication system has a great asset: Its semantics is in- herent to the gestures used to communicate. This is lacking in speech. In speech, or at least in modern speech, the meaning of the words and the phono-articulatory actions necessary to pronounce them are unrelated. This fact suggests that a nec- essary step for speech evolution was the transfer of gestural meaning, intrinsic to gesture itself, to abstract sound meaning. From this follows a clear neurophysio- logical prediction: Hand/arm and speech gestures must be strictly linked and must, at least in part, share a common neural substrate.

A number of studies prove that this is true. TMS experiments showed that the excitability of the hand motor cortex increases during both reading and spontaneous speech (Meister et al. 2003, Seyal et al. 1999, Tokimura et al. 1996). The effect is limited to the left hemisphere. Furthermore, no language-related effect is found in the leg motor area. Note that the increase of hand motor cortex excitability cannot be attributed to word articulation because, although word articulation recruits motor cortex bilaterally, the observed activation is strictly limited to the left hemisphere. The facilitation appears, therefore, to result from a coactivation of the dominant hand motor cortex with higher levels of language network (Meister et al. 2003).

Gentilucci et al. (2001) reached similar conclusions using a different approach. In a series of behavioral experiments, they presented participants with two 3-D objects, one large and one small. On the visible face of the objects there were either two crosses or a series of dots randomly scattered on the same area occupied by the crosses. Participants were required to grasp the objects and, in the condition in which the crosses appeared on the object, to open their mouth. The kinematics of hand, arm, and mouth movements was recorded. The results showed that lip aperture and the peak velocity of lip aperture increased when the movement was directed to the large object.

In another experiment of the same study Gentilucci et al. (2001) asked par- ticipants to pronounce a syllable (e.g., GU, GA) instead of simply opening their mouth. It was found that lip aperture was larger when the participants grasped a larger object. Furthermore, the maximal power of the voice spectrum recorded during syllable emission was also higher when the larger object was grasped.

Most interestingly, grasping movements influence syllable pronunciation not only when they are executed, but also when they are observed. In a recent study (Gentilucci 2003), normal volunteers were asked to pronounce the syllables BA or GA while observing another individual grasping objects of different size. Kine- matics of lip aperture and amplitude spectrum of voice was influenced by the grasping movements of the other individual. Specifically, both lip aperture and

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voice peak amplitude were greater when the observed action was directed to larger objects. Control experiments ruled out that the effect was due to the velocity of the observed arm movement.

Taken together, these experiments show that hand gestures and mouth gestures are strictly linked in humans and that this link includes the oro-laryngeal move- ments used for speech production.

Auditory Modality and Mirror-Neuron Systems

If the meaning of manual gestures, understood through the mirror-neuron mech- anism, indeed transferred, in evolution, from hand gestures to oro-laryngeal ges- tures, how did that transfer occur?

As described above, in monkeys there is a set of F5 mirror neurons that discharge in response to the sound of those actions that, when observed or executed by the monkey, trigger a given neuron (Kohler et al. 2002). The existence of these audio- visual mirror neurons indicates that auditory access to action representation is present also in monkeys.

However, the audio-visual neurons code only object-related actions. They are similar, in this respect, to the “classical” visual mirror neurons. But, as discussed above, object-related actions are not sufficient to create an efficient intentional communication system. Therefore, words should have derived mostly from as- sociation of sound with intransitive actions and pantomimes, rather than from object-directed actions.

An example taken from Paget (1930) may clarify the possible process at work. When we eat, we move our mouth, tongue, and lips in a specific manner. The observation of this combined series of motor actions constitutes the gesture whose meaning is transparent to everybody: “eat.” If, while making this action, we blow air through the oro-laryngeal cavities, we produce a sound like “mnyam-mnyam,” or “mnya-mnya,” words whose meaning is almost universally recognized (Paget 1930). Thus through such an association mechanism, the meaning of an action, naturally understood, is transferred to sound.

It is plausible that, originally, the understanding of the words related to mouth actions occurred through activation of audio-visual mirror neurons related to in- gestive behavior (see Ferrari et al. 2003). A fundamental step, however, toward speech acquisition was achieved when individuals, most likely thanks to improved imitation capacities (Donald 1991), became able to generate the sounds originally accompanied by a specific action without doing the action. This new capacity should have led to (and derived from) the acquisition of an auditory mirror system, developed on top of the original audio-visual one, but which progressively became independent of it.

More specifically, this scenario assumes that, in the case discussed above, the premotor cortex became progressively able to generate the sound “mnyam- mnyam” without the complex motor synergies necessary for producing ingestive

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action, and, in parallel, neurons developed able to both generate the sound and discharge (resonate) in response to that sound (echo-neurons). The incredibly confusing organization of Broca’s area in humans, where phonology, semantics, hand actions, ingestive actions, and syntax are all intermixed in a rather restricted neural space (see Bookheimer 2002), is probably a consequence to this evolutive trend.

Is there any evidence that humans possess an echo-neuron system, i.e., a system that motorically “resonates” when the individual listens to verbal material? There is evidence that this is the case.

Fadiga et al. (2002) recorded MEPs from the tongue muscles in normal volun- teers instructed to listen carefully to acoustically presented verbal and nonverbal stimuli. The stimuli were words, regular pseudowords, and bitonal sounds. In the middle of words and pseudowords either a double “f” or a double “r” were em- bedded. “F” is a labio-dental fricative consonant that, when pronounced, requires slight tongue mobilization, whereas “r” is linguo-palatal fricative consonant that, in contrast, requires a tongue movement to be pronounced. During the stimulus presentation the participants’ left motor cortices were stimulated.

The results showed that listening to words and pseudowords containing the dou- ble “r” determines a significant increase of MEPs recorded from tongue muscles as compared to listening to words and pseudowords containing the double “f” and listening to bitonal sounds. Furthermore, the facilitation due to listening of the “r” consonant was stronger for words than for pseudowords.

Similar results were obtained by Watkins et al. (2003). By using TMS tech- nique they recorded MEPs from a lip (orbicularis oris) and a hand muscle (first interosseus) in four conditions: listening to continuous prose, listening to nonverbal sounds, viewing speech-related lip movements, and viewing eye and brow move- ments. Compared to control conditions, listening to speech enhanced the MEPs recorded from the orbicularis oris muscle. This increase was seen only in response to stimulation of the left hemisphere. No changes of MEPs in any condition were observed following stimulation of the right hemisphere. Finally, the size of MEPs elicited in the first interosseus muscle did not differ in any condition.

Taken together these experiments show that an echo-neuron system exists in humans: when an individual listens to verbal stimuli, there is an activation of the speech-related motor centers.

There are two possible accounts of the functional role of the echo-neuron sys- tem. A possibility is that this system mediates only the imitation of verbal sounds. Another possibility is that the echo-neuron system mediates, in addition, speech perception, as proposed by Liberman and his colleagues (Liberman et al. 1967, Liberman & Mattingly 1985, Liberman & Wahlen 2000). There is no experimental evidence at present proving one or another of the two hypotheses. Yet, is hard to believe that the echo-system lost any relation with its original semantic function.

There is no space here to discuss the neural basis of action word semantics. However, if one accepts the evolutionary proposal we sketched above, there should be two roots to semantics. One, more ancient, is closely related to the action

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mirror-neuron system, and the other, more recent, is based on the echo-mirror- neuron system.

Evidence in favor of the existence of the ancient system in humans has been recently provided by EEG and fMRI studies. Pulvermueller (2001, 2002) com- pared EEG activations while subjects listened to face- and leg-related action verbs (“walking” versus “talking”). They found that words describing leg actions evoked stronger in-going current at dorsal sites, close to the cortical leg-area, whereas those of the “talking” type elicited the stronger currents at inferior sites, next to the motor representation of the face and mouth.

In an fMRI experiment, Tettamanti et al. (M. Tettamanti, G. Buccino, M.C. Saccuman, V. Gallese, M. Danna, P. Scifo, S.F. Cappa, G. Rizzolatti, D. Perani & F. Fazio, submitted manuscript) tested whether cortical areas active during action observation were also active during listening to action sentences. Sentences that describe actions performed with mouth, hand/arm, and leg were used. The presentation of abstract sentences of comparable syntactic structure was used as a control condition. The results showed activations in the precentral gyrus and in the posterior part of IFG. The activations in the precentral gyrus, and especially that during listening to hand-action sentences, basically corresponded to those found during the observation of the same actions. The activation of IFG was particularly strong during listening of mouth actions, but was also present during listening of actions done with other effectors. It is likely, therefore, that, in addition to mouth actions, in the inferior frontal gyrus there is also a more general representation of action verbs. Regardless of this last interpretation problem, these data provide clear evidence that listening to sentences describing actions engages visuo-motor circuits subserving action representation.

These data, of course, do not prove that the semantics is exclusively, or even mostly, due to the original sensorimotor systems. The devastating effect on speech of lesions destroying the perisylvian region testifies the importance in action un- derstanding of the system based on direct transformation of sounds into speech motor gesture. Thus, the most parsimonious hypothesis appears to be that, during speech acquisition, a process occurs somehow similar to the one that, in evolution, gave meaning to sound. The meaning of words is based first on the old nonverbal semantic system. Subsequently, however, the words are understood even without a massive activation of the old semantic system. Experiments, such as selective inhibition through TMS or electrical stimulation of premotor and parietal areas, are needed to better understand the relative role of the two systems in speech perceptions.

ACKNOWLEDGMENTS

This study was supported by EU Contract QLG3-CT-2002-00746, Mirror, EU Contract IST-2000-28159, by the European Science Foundation, and by the Italian Ministero dell’Università e Ricerca, grants Cofin and Firb RBNEO1SZB4.

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The Annual Review of Neuroscience is online at http://neuro.annualreviews.org

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MIRROR NEURONS C-1

Figure 1 Lateral view of the monkey brain showing, in color, the motor areas of the frontal lobe and the areas of the posterior parietal cortex. For nomenclature and definition of frontal motor areas (F1–F7) and posterior parietal areas (PE, PEc, PF, PFG, PG, PF op, PG op, and Opt) see Rizzolatti et al. (1998). AI, inferior arcuate sulcus; AS, superior arcu- ate sulcus; C, central sulcus; L, lateral fissure; Lu, lunate sulcus; P, principal sulcus; POs, parieto-occipital sulcus; STS, superior temporal sulcus.

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Figure 2 Mirror neuron responses to action observation in full vision (A and C) and in hidden condition (B and D). The lower part of each panel illustrates schematical- ly the experimenter’s action as observed from the monkey’s vantage point. The asterisk indicates the location of a stationary marker attached to the frame. In hid- den conditions the experimenter’s hand started to disappear from the monkey’s vision when crossing this marker. In each panel above the illustration of the experi- menter’s hand, raster displays and histograms of ten consecutive trials recorded are shown. Above each raster, the colored line represents the kinematics of the experi- menter’s hand movements expressed as the distance between the hand of the exper- imenter and the stationary marker over time. Rasters and histograms are aligned with the moment when the experimenter’s hand was closest to the marker. Green vertical line: movement onset; red vertical line: marker crossing; blue vertical line: contact with the object. Histograms bin width = 20 ms. The ordinate is in spike/s. (From Umiltà et al. 2001).

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MIRROR NEURONS C-3

Figure 3 Cortical activations during the observation of biting made by a man, a monkey, and a dog. From Buccino et al. 2004.

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Figure 4 Cortical activations during the observation of communicative actions. For other explanations see text. From Buccino et al. 2004.

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Consciousness and Cognition 22 (2013) 1152–1161

Contents lists available at SciVerse ScienceDirect

Consciousness and Cognition

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o n c o g

Mirror neurons and their function in cognitively understood empathy

1053-8100/$ – see front matter � 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.concog.2013.03.003

⇑ Corresponding author. Fax: +39 02 72342280. E-mail addresses: [email protected] (A. Corradini), [email protected] (A. Antonietti).

Antonella Corradini ⇑, Alessandro Antonietti Department of Psychology, Catholic University of the Sacred Heart, Largo Gemelli 1, 20123 Milano, Italy

a r t i c l e i n f o a b s t r a c t

Article history: Available online 11 April 2013

Keywords: Mirror neurons Empathy Reenactive empathy Rational explanation Social cognition Mindreading Theory–theory Simulation theory Emotion Intention understanding

The current renewal of interest in empathy is closely connected to the recent neurobiologi- cal discovery of mirror neurons. Although the concept of empathy has been widely deployed, we shall focus upon one main psychological function it serves: enabling us to understand other peoples’ intentions. In this essay we will draw on neuroscientific, psycho- logical, and philosophical literature in order to investigate the relationships between mir- ror neurons and empathy as to intention understanding. Firstly, it will be explored whether mirror neurons are the neural basis of our empathic capacities: a vast array of empirical results appears to confirm this hypothesis. Secondly, the higher level capacity of reenactive empathy will be examined and the question will be addressed whether philosophical anal- ysis alone is able to provide a foundation for this more abstract level of empathy. The con- clusion will be drawn that both empirical evidence and philosophical analysis can jointly contribute to the clarification of the concept of empathy.

� 2013 Elsevier Inc. All rights reserved.

1. Introduction

The mirror neuron system (MNS) has been recently proposed as the biological basis of social cognition (e.g., Pineda, 2009). This encompasses a broad range of phenomena, which includes, among others, empathy (Gallese, Gernsbacher, Heyes, Hick- ok, & Iacoboni, 2011, Question 6). The term ‘‘empathy’’ is used to denote different phenomena (Roganti & Ricci Bitti, 2012). It is sometimes deployed to refer to simple forms of behavioural sharing, as occurs in emotional contagion: when a person is performing an action which is usually associated with the experience of a given emotion, another displays the same behav- iour (de Vignemont & Singer, 2006). This is the case of a baby who begins crying because another baby close to her is crying or the case of laughter which spreads in a group even though people are not aware of why the others are laughing. On the other hand, empathy can be conceived of as a mainly cognitive phenomenon, which allows us to figure out the propositional attitudes that are at the basis of another’s deciding, planning, and acting. Emotional aspects are not excluded, but they play a minor role in the empathic process.

In the light of this special issue’s topic, empathy can be conceived of as a person’s capacity to understand what others intend to do by experiencing the sensations, emotions, feelings, thoughts, beliefs, and desires which the other is experiencing (or has previously experienced). The assumption is that, if we experience the mental states of a fellow person, we can under- stand her reasons for her acting in a given way, and thus understand the intentions underlying her behaviour. For instance, if we realise, by watching Tom, that he has been offended by Dick and that he is now becoming angrier and angrier as a con- sequence of such an offence, we can understand why Tom behaves aggressively towards Dick. In turn, the comprehension of another’s mental states is based, beside verbal communication, on the overt behaviour displayed by her (Avenanti & Aglioti,http://crossmark.crossref.org/dialog/?doi=10.1016/j.concog.2013.03.003&domain=pdfhttp://dx.doi.org/10.1016/j.concog.2013.03.003mailto:[email protected]mailto:[email protected]http://dx.doi.org/10.1016/j.concog.2013.03.003http://www.sciencedirect.com/science/journal/10538100http://www.elsevier.com/locate/concog

A. Corradini, A. Antonietti / Consciousness and Cognition 22 (2013) 1152–1161 1153

2006), thus the observation of others’ bodily signals can be an important source of intention ascription. For instance, as sug- gested by Wolpert, Doya, and Kawato (2003), facial expressions – one of the main body signals we use to communicate, intentionally or incidentally, our emotional state to the others – can be seen as actions aimed at revealing the subject’s intentions.

The function of empathy in understanding others’ intentions can be analysed both from a scientific and a philosophical point of view. The aim of this essay is to address this topic from both perspectives. From the viewpoint of scientific inquiry, the distinction between different forms of detecting others’ intentions is taken into account by referring to recent psycho- logical literature. This will allow us to identify the specific form of empathy which is allegedly associated with MNS. Then, empirical data supporting the role of MNS in empathy will be shortly reviewed. The first section of the essay will end with some critical remarks about the need for conceptual clarification when appealing to MNS to ground empathy. These com- ments, by stressing the necessity of a fine-tuned analysis of such conceptual issues, will build the bridge to the philosophical section. This mainly focuses on whether reenactive empathy, that is to say cognitively understood empathy, can be con- ceived of as a genuine epistemic capacity, able to justify rational explanation. After a short introduction to the topic of empa- thy in contemporary social sciences, part 3.2. will be devoted to a defence of the soundness of rational explanation against criticisms raised by Hempel and other authors belonging to the empiricist tradition. In part 3.3, then, two arguments will be subjected to scrutiny, whose aim is to show that only reenactive empathy is able to ensure the validity of rational explana- tion. The upshot will be that neither argument proves to be conclusive. This result, however, does not definitively rule out empathy as an original kind of knowledge, since empirical evidence based on mirror neurons might offer some support to this epistemological thesis, in particular if basic kinds of empathy are taken into consideration.

2. Empathy and MNS from the point of view of psychology and neuroscience

2.1. Mirroring and mentalising mechanisms underlying empathy

Empathy is a complex phenomenon involving different aspects and dimensions. In fact, the understanding of others’ intentions through the experience of their mental states may be underwritten by different processes. On the one hand, as shown by the example reported in the previous section, we can immediately understand the reasons for Tom’s aggressive behaviour on the basis of the perception of his face and/or the tone of his voice. We establish a direct connection between what Tom looks like (in terms of bodily appearance and bodily movements), his mental states, and his acts. On the other hand, we can understand Tom’s intentions by integrating the perceptual information Tom provides us with and some infer- ences based on contextual cues (for instance, the presence of other people on the scene who are mocking him), specific no- tions we have about Tom (for instance, remembering that Tom is a choleric guy), and abstract concepts (for instance, our conviction that an offended man should always take revenge).

In the fields of psychology and the neurosciences some distinctions have been drawn in the attempt to clarify the mech- anisms underlying the understanding of others’ intentions. A relevant starting point may be the distinction which has been made, under different concepts and linguistic labels, between a system which allows human beings to comprehend imme- diately others’ intentions and a system which allows humans to reach such an outcome through an inferential process which implies the mediating role of some forms of reasoning.

This distinction relies on a more fundamental distinction which has been recurrently proposed by different authors in recent years in the domain of thinking and decision-making processes (Sloman, 1996), namely, the distinction between the so-called System 1 and System 2. System 1 (Stanovich & West, 2000) – also labelled as intuitive (Pretz, 2008), experien- tial (Slovic, Finucane, Peters, & MacGregor, 2002), tacit (Hogarth, 2001), impression-based (Kahneman, 2003) – is fast and action-oriented; it is activated unintentionally and its functioning is rigid and partially behind the control of the individual. Usually it operates effortlessly on the basis of associations. System 2 (Stanovich & West, 2000) – also called analytical (Slovic et al., 2002), deliberative (Hogarth, 2001), judgment-based (Kahneman, 2003), rational (Epstein, 1994) – operates slowly, intentionally, and flexibly, predominantly on the basis of abstract representations and logical rules. Usually it is not emotion- ally charged. The functioning of System 2 may fail to be optimal because of the excessive cognitive load it requires, its slow- ness, and the large amount of effort its activation needs.

In this vein, with specific reference to social cognition, Bohl and van den Bos (2012) proposed the distinction between Type 1 and Type 2 process. The former is fast, efficient, stimulus-driven, and lacks flexibility. The latter is slow, involves a high cog- nitive load and elaboration, is flexible and accessible to consciousness. With a more specific focus on processes involved in understanding other people’s intentions, Waytz and Mitchell (2011) distinguished between mirroring and self-projection mechanisms. The first mechanism enables us to understand other people by experiencing vicariously their mental states: thanks to such a mechanism, the others’ mental states are mirrored in our mind. Through the second mechanism we project our mental states onto the situation of another individual, so to infer her mental states. According to the authors, the two mechanisms involve different degrees of immediacy in others’ understanding. Mirroring is a sort of on-line process which al- lows us to resonate immediately according to what another person is experiencing; self-projection, by contrast, implies imag- ining off-line what we should experience if we were in the other’s shoes and then attributing such an experience to her.

The distinction between mirroring and self-projection overlaps partially the distinction between mirroring and mentalis- ing (Chiavarino, Apperly, & Humphreys, 2012). The mirroring system responds to observation of others’ acts and seems to

1154 A. Corradini, A. Antonietti / Consciousness and Cognition 22 (2013) 1152–1161

code their goals immediately by establishing purely behavioural relations between the perceptual appearance of the actor and her corresponding intentions. Mentalising instead requires inferences about the mental states which are at the basis of the behavioural relations. More precisely, the second system has two subcomponents: a representational one, which serves the task to represent the actor’s intention as a mental state (but not as a behavioural relation), and a conceptual com- ponent ‘‘representing the semantic and logical properties of intentions, abstractly reasoning over these properties, and relat- ing them to other mental states’’ (Chiavarino et al., 2012, p. 286).

2.2. Mirror neurons and empathy: empirical data

The neural circuits constituting MNS have been proposed as the best candidate for the biological basis of empathy, which is to be thought of as the expression of the mirroring process. In fact, MNS has been invoked as a putative interpretation of empathy and some experimental findings have been taken as evidence supporting the involvement of MNS in empathy (Gal- lese, 2001, 2003; Iacoboni, 2009; Preston & de Waal, 2002).

First of all, it is documented that humans, when watching people showing facial expressions corresponding to well-de- fined emotions, covertly activate the same muscles which are involved in the creation of those expressions (Dimberg, Thun- berg, & Elmehed, 2000). Moreover, if people are prevented from automatically imitating the muscle contractions of the faces they are exposed to (for instance, by compelling them to keep a pencil with the teeth transversal to the mouth), they become less able to detect the emotional expression of the observed faces (Niedenthal, Barsalou, Winkielman, Krauth-Gruber, & Ric, 2005). This experimental finding supports analogous results observed in patients affected by the Moebius syndrome, which impedes them to move their facial muscles: as a consequence of such an impairment, these patients fail to recognise the emotions expressed by others (Cole, 2001). Finally, it is worth noting that the same cortical areas are activated when people observe and imitate faces expressing emotions (Leslie, Johnson-Frey, & Grafton, 2004). Hence, it is proved that, in emotion recognition, observation and action are linked together, as in the case of the functional actions directed at manipulating things, which have been the main topic of investigation in MNS field.

These findings, however, only concern emotion recognition, which is not empathy, but rather its precursor or precondi- tion. Further empirical evidence is required. Indeed, other studies showed that the link between observation and perception also regards empathy. For instance, if individuals are paired with a confederate who imitates their postures, gestures, and body movements during the execution of a joint task, they perceive the confederate as more agreeable than controls paired to a non-imitating confederate do (Chartrand & Bargh, 1999). In addition, individuals who spontaneously imitated the behaviour of the confederate scored higher on an empathy scale subsequently, showing a positive relation between the fre- quency of imitative behaviours and the empathy rates (Chartrand & Bargh, 1999).

Two emotional reactions have been often investigated in the attempt to prove the involvement of MNS in empathy: pain and disgust. As to pain, Avenanti, Bueti, Galati, and Aglioti (2005) recorded the excitability of the muscle of the hand which generates an approaching movement toward a noxious stimulus (a needle): when people looked at a video showing other people whose hand was penetrated by a needle in the same point, the excitability of the muscle decreased (as if they were trying to move away the hand from the needle); in addition, the reduction of the excitability of the muscle was proportional to the estimated level of pain the subjects attributed to other people when their hand was penetrated by the needle (see also Avenanti, Minio-Paluello, Sforza, & Aglioti, 2009; Valeriani et al., 2008).

As far as the brain counterparts of pain experience are concerned, it was showed that neurons in the anterior cingulate cortex responding to painful stimuli applied to the subject’s hand also fired when the subject observed another person being stimulated by the same noxious stimuli (Hutchison, Davis, Lozano, Tasker, & Dostrovsky, 1999). Anterior cingulate cortex, together with some regions of the insula, was also activated by observing relatives who were not currently exposed to pain- ful stimuli, but would be stimulated painfully later (Singer et al., 2004). Hence, not only the direct observation of suffering people, but also the prefiguration of a future pain affecting others activate the brain areas corresponding to the actual expe- rience of pain in first person.

The same message is provided by studies concerning the neural counterparts of disgust. It has been proved that the same brain structure (the insula, in this case), which is active when the individual experiences disgust personally, is activated even when the individual looks at faces expressing disgust and that the intensity of such an activation is proportional to the level of disgust expressed by the face (Phillips et al., 1997). The evidence was later supported by recording the activity of neurons in the anterior part of the insula through electrodes implanted in the brain of epileptic patients (Krolak-Salmon et al., 2003). A clear proof that the same neural counterparts are involved in experiencing disgust and observing other people experienc- ing that emotion was provided by Wicker et al. (2003) in a fMRI study where the same participants were both exposed to disgusting odours and to pictures of persons smelling the same odours.

The impairment in experiencing negative emotions is associated with the impairment of recognising similar emotions in other people. In fact, a case was reported of a patient with brain lesions in the putamen and in the insula who failed to sub- jectively experience disgust (and, as a consequence, to react to disgusting situations appropriately) and also was not able to detect disgust in other people by observing their facial expressions or by listening to non-verbal sounds which they pro- duced, as well as to the prosodic aspects of their speech (Calder, Keane, Manes, Antoun, & Young, 2000). A similar case was successively reported by Adolphs, Tranel, and Damasio (2003).

When trying to find evidence that MNS is specifically involved in empathy, we can point to the fact that the activation of brain areas included in MNS has been recorded in participants both when they were simply looking at actors showing facial

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expressions whose emotional meaning corresponded to that of the story they were telling (Decety & Chaminade, 2003) and when they were asked to identify the emotional states of actors by observing their body postures, gestures, and facial expres- sions (Lawrence et al., 2006). Further support came from the experiment executed by Schulte-Rüther, Markowitsch, Fink, and Piefke (2007): mirror-neuron mechanisms were activated when participants, exposed to facial expressions, had to identify both the emotions concurrently experienced by themselves and the emotions expressed by the others’ faces.

The involvement of MNS in empathy is also proved by correlational studies. Two investigations demonstrated that the level of emotional empathy developed by the participants was correlated to the intensity of the activity of premotor areas, presumably containing mirror neurons, when the participants were asked to look at other people carrying out the act of grasping with different intentions, as suggested by contextual hints (Kaplan & Iacoboni, 2006) or to listen to sounds pro- duced by human actions (Gazzola, Aziz-Zadeh, & Keysers, 2006). More specifically, participants who showed higher activa- tion of brain areas involved in MNS when looking at facial expressions by focussing on their emotional valence (Schulte- Rüther et al., 2007) obtained high scores on empathy scales.

MNS, together with other brain structures such as the limbic system and the insula, constitutes a large neural circuitry which has been proved to be activated by both the execution, through imitation, and observation of facial expressions asso- ciated to emotional experiences (Carr, Iacoboni, Dubeau, Mazziotta, & Lenzi, 2003; Iacoboni & Lenzi, 2002). The association between MNS and both the subjective experience of emotions and the detection of the same emotions in others through the observation of their behaviour is further supported by a fMRI study which showed that the activation of MNS in preadoles- cents while observing and imitating emotional facial expressions is positively correlated with the level of empathic skills (Pfeiffer, Iacoboni, Mazziotta, & Dapretto, 2008). An additional support is provided by clinical studies carried out with people affected by autism. On the one hand these patients – who are impaired in recognising emotions from others’ facial expres- sions and to imitate such expressions – fail to show the usual reactions when looking at other people being affected by pain- ful stimuli (Minio-Paluello, Baron-Cohen, Avenanti, Walsh, & Aglioti, 2009). On the other hand people with autism show deficits in MNS functioning and their level of activity of MNS is reduced in correspondence with the level of severity of the pathology (Dapretto et al., 2006).

2.3. Mirror neurons and empathy: conceptual problems

One of the main messages which are associated to the findings concerning the involvement of MNS in the understanding of others’ mental states, including intentions, is that such an understanding does not exclusively depend on linguistic and mentalistic processes (Gallese, 2001, p. 34). On the contrary, intentions are embodied. Such an embodiment is shared both by the actor and the observer and relies on the motor schema of action. When the motor schema of the actor matches a mo- tor schema in the repertoire of the observer, the intended meaning of the action is detected (Gallese, 2001, p. 36). If this gen- eral framework is applied to empathy, the consequence is that empathy is grounded in the experience of the lived body: others are conceived ‘‘not as bodies endowed with a mind but as persons like us’’ (Gallese, 2001, p. 43). In this way we can recognise why persons behave in a certain manner.

In some circumstances, the comprehension of the intentions of others’ behaviour occurs predominantly on the basis of the emotions they are experiencing rather than of the functions of the actions they are performing. When this happens, empirical findings summarised above suggest that MNS is involved, either because some cerebral areas belonging to MNS are directly activated or because other brain structures, connected to the main mirror-neuron areas, are activated, such that they successively involve the proper mirror-neuron areas. In any case, the resulting outcome is that the same brain struc- tures, which are activated when we experience the affective state the other is experiencing, are activated. This would lead the affective states of other people to resonate in the mind of the perceiver (Gallese, 2001, p. 38; Rizzolatti & Sinigaglia, 2006, p. 121) or, put differently, would generate in the perceiver a sort of inner imitation of what the other is feeling (Iacoboni, 2008, chap. 4). Another way of thinking of this is that the cerebral system of the observer would be activated as if she were behaving as the observed human being. This occurs because the observed behaviour is translated into a program which acts as a sort of signal (efference copy signal) which enables the simulation of the behaviour (Gallese, 2001, pp. 40–41). As a con- sequence, the other’s behaviour is modelled as an action thanks to the behavioural equivalence between the perceiver’s and the other’s actions (Gallese, 2001, p. 39). A first critical remark is that further clarification of the mental process supported by MNS during an empathic relation is required. Resonance, inner imitation, simulation, and modelling are different processes and the authors claiming that MNS grounds empathy should be more explicit and precise about the psychological counter- parts of the corresponding cerebral activations.

Whatever these processes may be which are supported by MNS and lead to empathy, authors maintaining that MNS is involved in empathy generally agree that intention understanding does not involve any form of abstract thought. To put it in the authors’ words, it is ‘‘non-predicative’’ (Gallese, 2001, p. 44), ‘‘without verbal mediation’’ (Rizzolatti & Sinigaglia, 2006, p. 120), ‘‘without the need of theorising’’ (Gallese, 2001, p. 41), ‘‘without propositional attitudes’’ (Gallese, 2001, p. 41), ‘‘non-inferential’’ (Gallese, 2001, p. 44; Rizzolatti & Sinigaglia, 2006, p. 174), ‘‘without any knowledge operation’’ (Riz- zolatti & Sinigaglia, 2006, p. 127), ‘‘not needing cognitive processes’’ (Rizzolatti & Sinigaglia, 2006, p. 174), ‘‘pre-reflective’’ (Iacoboni, 2009, p. 666). In these authors’ view, MNS leads us to comprehend others’ experience in the absence of any con- ceptual representation and inference. Now, how should this form of understanding be conceived? This is a list of the adjec- tives which are attributed to it: ‘‘direct’’ (Gallese, 2001, p. 41), ‘‘immediate’’ (Gallese, 2001, p. 41; Rizzolatti & Sinigaglia, 2006, p. 127), ‘‘effortless’’ (Iacoboni, 2009, p. 666), ‘‘automatic’’ (Gallese, 2001, p. 41; Iacoboni, 2009, p. 666), ‘‘implicit’’ (Gal-

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lese, 2001, p. 41), ‘‘unconscious’’ (Gallese, 2001, p. 41), ‘‘subpersonal’’ (Gallese, 2001, p. 42 and 46). Here, too more precision seems to be required (Debes, 2009). In fact these attributes have different meanings and do not implicate one another. For instance, pure knowledge operations and cognitive processes, with no form of embodiment, can also be immediate and effortless, if adequately trained. Also the meaning of ‘‘automatic’’ and ‘‘unconscious’’ should be specified. A process can be automatic by its very nature or because it has become such after having been carried out for a long time with effort and the labour of reasoning. The same is true of the unconscious character of intention understanding: is it a process which has become unconscious as a consequence of its automatisation or because it has always been unconscious? In other words: the process might be conscious (and involving effort) when the individual is trying to learn to carry it out, but it becomes unconscious (and effortless) when she had learnt to master it. In addition: does the unconscious character of the process make reference to how the process develops or to the outcome of the process? We can be unaware of how we compute the sum 5 + 2, but we are aware of the output of the process (and also of the fact that we are computing the sum). Also the claim that intention understanding supported by MNS through empathy fails to involve knowledge and cognitive mech- anisms can be questioned. As noted by Roganti and Ricci Bitti (2012, pp. 583–584), appraisal processes are always implied in emotion comprehension, and thus an interpretative component can never be discarded, otherwise only a form of emotional synchronisation or synthonisation, but not a real understanding, occurs. Thus, the specific forms of cognition which should be excluded by the kind of empathy supported by MNS have to be clarified, since it has been proved that other cortical re- gions, beside MNS, are involved in cognitive manifestations of empathy (Shamay-Tsoory, Aharon-Peretz, & Perry, 2008).

In conclusion, it appears that a more fine-grained analysis of the features of the empathic relation supported by MNR is needed. To this end, this issue has to be addressed from the philosophical perspective, which we turn to now.

3. From mirror neurons to reenactive empathy

3.1. Empathy as reenactive empathy

As the first part of this essay has shown, the renewed, current interest in empathy is strictly related to empirical research in the fields of neurobiology and psychology. In particular, the discovery of MNS in monkeys has given new impulse to the scientific treatment of empathy. However, the notion of empathy has a long philosophical tradition, characterised by many ramifications and several divergent approaches (for an informed reconstruction of the history of empathy see Stüber, 2006, Introduction, and 2008). As far as philosophy of the social sciences is concerned, the most influential twentieth century sup- porter of empathy has been the philosopher of history Robert Collingwood (1949) who, against explanatory monism, main- tained that explanation in history requires an essential empathic component. In fact, we cannot explain the behaviour of a historical character without re-enacting her intentions, beliefs, desires and choices. Yet, the role of reenactive empathy has not always been positively evaluated within the philosophy of the social sciences, partly because it introduces a sharp dual- ism between natural and social sciences, partly because it appears to represent a capitulation to any sort of subjectivism and arbitrariness (see Popper’s criticism of the epistemological role of empathy in Popper, 1972, 4.12). In recent years, however, authors such as Jane Heal and Karsten Stüber have revived the fortunes of empathy and have argued in favour of a strict correlation between rational explanation and empathy as a fundamental epistemic capacity. Most part of what follows is a discussion about the theses put forward by both authors.

3.2. Rational explanation

As is well known, there are two main ways of conceiving explanation in folk-psychology. The first is theory–theory and the second is simulation theory.

According to theory–theory, human actions are explained on the basis of the classical Hempelian method, which, although imperfect in a number of ways, nonetheless maintains its fundamental validity. What is essential in this method is the presence within the explanans of empirical laws having the form of universal conditionals. From the point of view of theory–theory supporters, then, action explanation is an empirical theory, which explains agents’ actions through empirical laws, just as any empirical theory explains the behaviour of certain objects. The laws may be different from some other empirical theories, since in folk-psychology they often are probabilistic or ceteris paribus laws; nonetheless, the explanatory structure is the same. By contrast, according to simulation theory, an agent’s behaviour is explained through simulation of the reasons, beliefs and desires which move the agent to action.

An example of the theory–theory paradigm consists in the last of the three inferences involved in a successfully per- formed false belief task.

‘‘Predicting where Maxi will look for the chocolate.

i. Maxi wants to eat the chocolate, and he believes that the chocolate is in cupboard, and he believes that looking for the chocolate in cupboard is a means of satisfying one’s desire of eating it.

ii. Central action principle: If somebody desires x and believes that A-ing is a means of achieving x, then, ceteris paribus, he will do A.

iii. Max will look for the chocolate in cupboard.’’ (Stüber, 2006, pp. 109–110).

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The issue at stake is to clarify the nature of Central Action Principle (also named by Kim (1984, 1998) Desire/Belief/Action Principle – DBA), which in the inferential scheme fulfils the function of a general law. For theory–theory supporters this prin- ciple is an empirical law expressing a kind of nomological necessity and its presence is necessary. The notion of nomological necessity is, in fact, essential in order to define the relation of causal explanation.

Critics of the theory–theory paradigm, however, cast doubts on the empirical nature of laws like DBA. What they question is not their general character; rather, critics point at the fact that they do not express a nomological necessity but a logical– analytical necessity, which sometimes is defined as a ‘‘rational’’ necessity (Dray, 1957). In other words, principles of this kind are principles that define the notion of rationality. They are the axioms of practical rationality, formally encoded in practical syllogisms (or practical inferences) (Anscombe, 1957; von Wright, 1971).

Hempel’s criticism of rational explanation is well known (Hempel, 1965, chap. 5). If the DBA principle is a rationality ax- iom, it cannot be the object of empirical confirmation and, thus, it cannot be considered as a principle endowed with explan- atory capacity. To avoid this consequence it is necessary to modify DBA to the following principle, DBA�.

Central action principle revised: If somebody desires x and believes that A-ing is a means of achieving x and she is a rational agent, then, ceteris paribus, she will do A.

However, this move is fatal to rational explanation, since a rationality clause cannot be included among the particular facts of a law that claims to contribute to the definition of rationality itself. Indeed, to obtain confirmation of a law like DBA�

we must be in the business of establishing the truth of the antecedent, including the rationality clause. But, how is it possible to establish an agent’s rationality, if we need the principle DBA� itself to define the rationality notion?

The contrast between rational and nomological explanation seems to be so stark as to only allow two possibilities. Either we maintain that explanation should be nomological in the human sciences just as in the physical sciences, which almost necessarily leads to a naturalistic re-interpretation of folk-psychology. Or we give up the claim that actions are explainable as human actions and fall back on the less ambitious idea that they can only be the object of understanding; that is to say they are behaviours that we can interpret in the light of an agent’s subjectivity but that have their cause elsewhere. Is there a way out of this dilemma?

Borrowing from Stüber (2003) we assume that principles like DBA can be conceived of both as analytical principles and as empirical generalisations. If they are understood as analytical principles, they express a necessity of a conceptual kind and have, on top of that, a normative meaning, as they formalize a correct way of reasoning. An agent who does not abide by them does not reason correctly and, as a consequence, does not decide correctly. These principles, however, can also be con- ceived of as empirical generalisations, inasmuch as they describe the way agents ‘‘in flesh and blood’’ reason and take deci- sions. In this latter meaning, and only in this latter meaning, they are falsifiable by experience. ‘‘The distinction between understanding a general statement as the articulation of a normative standard or as the description of a regularity in beha- vior points to different functions of the same statements in different contexts’’ (Stüber, 2003, p. 268).

But why can they also be conceived of as empirical generalisations? Expanding on the previous argument, we can give the following answer. Analytically understood DBA principles define the concept of rationality. As we said before, they are ratio- nality axioms and, thus, define the way a real mind (or a mechanism like a mind) should function in order to be a mind that operates rationally. It is worth noting that, from this viewpoint, also principles belonging to scientific theories could be con- ceived of as axioms that define certain models of empirical reality. In this way theory confirmation would not be anything other than the confirmation of the fact that the model defined by the theory is actually instantiated in empirical reality.

Owing to this analysis of DBA, the rationality clause, which Hempel considered as a necessary condition in order to justify the explanatory character of practical argumentation, can now be put in the right place. For the previously mentioned rea- sons, such a clause must not be put among the other clauses of the conditional that makes the law. It must be considered, instead, as a fundamental presupposition, that is to say as a background assumption, that permits us the very use of those laws. In other words, it is the same assumption made in the practical–inferential model of rationality, understood as an explanatory model of empirical agents’ concrete actions. This assumption could be of course totally wrong, if the model did not work at all, that is to say if no set of actions did exist, which can be explained by any exemplification of the model. However, this can hardly be the case, since this would be tantamount to saying that the set of the actions to be rationally explained is empty. Instead, it is easier to falsify such a hypothesis on particular occasions, in which the action under scrutiny does not derive from true premises of the DBA principle. However, also on these particular occasions it is not the falsification of DBA as an analytical (logically correct) principle that occurs, but the falsification of the principle considered as an explan- atory scheme. Thus, in the end, it is the falsification of the validity of the principle in that particular case.

Yet, at this point a problem arises. The correctness of the DBA scheme can be justified by means of a priori reasons. It is an analytical principle and, therefore, it has to be founded in a similar way as those of the formal sciences. But what about DBA as an explanatory law, that is to say as the fundamental presupposition concerning the explanatory dimension of the prac- tical–inferential model in its application to reality?

3.3. Is reenactive empathy an epistemic capacity?

Authors such as Heal and Stüber answer this question by recourse to the empathy thesis. We are supposed to have the direct perception of the connections established by the DBA principle among our desires, our beliefs and the actions we per- form. This perception is a first-person perception. It is the agent’s ego who perceives the logic of her acting. At this point

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empathy enters the scene. The agent is able to put himself in others’ shoes, meaning not only that she succeeds in grasping the others’ point of view, but also in reenacting the same experiences which characterise others’ mental and emotive pro- cesses. In this way empathy becomes the epistemic element able to endow schemes like DBA with an explanatory dimension: that is to say empathy guarantees the soundness of their explanatory use. As Stüber puts it: ‘‘The special status of DBA just derives from the fact that we ourselves have access to our cognitive states and reasoning from the first person perspective and have to use this ability in a projective or reenactive manner in order to understand the reasons of other agents’’ (Stüber, 2003, pp. 275–276; Stüber, 2006, pp. 212–213).

But why should we resuscitate reenactive empathy or co-cognition (Heal, 2003, p. 97 ff) in order to account for the sound- ness of the practical inferential explanation of actions? Heal (2003) and Stüber (2006, p. 152 ff) put forward two arguments in favour of the epistemic relevance of empathy. In the remainder of this essay I will expound and comment on both arguments.

(A) The argument from the essential contextuality of thoughts as reasons

As the argument goes, theory–theory aims to deliver a complete theory of action, including both a formal inferential scheme to allow people’s thoughts to be related together until the final decision is taken and a criterion to objectively estab- lish the premises of the inferential scheme.

But such a theory does not exist, because there is no complete formal inferential scheme and, above all, there are no cri- teria to objectively establish the premises of the inferential scheme, as they are dependent on the context. In fact, according to the frame problem, in order to establish the premises it is necessary to know what are the relevant aspects for ends choice. But to understand what are the relevant beliefs for explaining an action it is necessary to understand what are the beliefs that are meaningful to themselves as a subject, and this is not possible without reenactive empathy.

Analysis of and comment on the argument. Three aspects of the previous argumentation should be distinguished.

a. Theory–theory is criticised because it is unable to deliver a complete theory of action: it only partly covers the process of practical decision. In particular, it cannot solve the problem of the premises identification. Thus the theory is insuf- ficient, since it is incomplete as regards its premises.

b. Theory–theory is criticised because it is objective, that is, it does not account for the first person’s perspective. c. Theory–theory is criticised because it cannot justify the attribution of a causal role to agents’ desires and beliefs when

these concern strictly subjective contents. But – as we learned from the contextuality argument – how is it possible to explain agents’ behaviours if we do not have any access to their subjectivity, that is, if we do not succeed in under- standing how and why these contents are meaningful to the agent? Such an access presupposes an original and irre- ducible capability to empathically identify ourselves with a subject different from us.

Now, our comment is that reenactive empathy may be needed, if it is needed at all, to provide a solution for the problem formulated at point c, but neither for the problem mentioned at point a nor for that at point b. Let us ask ourselves, in fact, what is needed to overcome incompleteness (point a).

A method is needed that is able to establish the premises, which, however, are formulated from the subject’s viewpoint. They are premises which do not express states of affairs of the agent’s life that can be described as causes or objective con- ditions of the agent’s conduct. The states of affairs corresponding to such premises are not characterised by empirically detectable properties, thus we cannot grasp them without taking into account the subjective framework in which they are situated. In other words, they are states of affairs that can be described as structurally identical with the desires and be- liefs from which our actions originate. Thus they presuppose the access to the first person’s perspective. We can then con- clude that in order to overcome the incompleteness of the theory we need to modify it so to make it able to express the first person’s perspective. What is it necessary for such a goal? To say that we need reenactive empathy appears to us to be too a hasty strategy. Instead, we need to replace the Hempelian D–N scheme with the P–I scheme of practical inference. Practical inference, in fact, consists in a general scheme including assertions of the goals to be reached (B(x, goal p) as premises, beliefs on the chain of actions to perform for reaching those goals (B(x, N(p � to do q) and, as a conclusion, the action the subject decides to perform (x does q). Premises and conclusion are not connected to each other by empirical laws, but by principles belonging to practical logic (epistemic and deontic logic at first place). It is this very essential aspect of P–I that makes it capable of expressing the first person’s perspective. Actually, the above outlined scheme works perfectly if we replace x with the indexical ‘‘I’’, a typical expression of the first person’s perspective. So far, however, no kind of reenactive empathy is needed. We are dealing with the first person’s perspective, which only requires the subject’s capacity to grasp the nexus be- tween the practical–inferential scheme and the world of her own desires and beliefs. To this end a form of self-perception or of self-awareness, but not of empathy is needed. Reenactive empathy could perhaps play a role at point c, when the P–I scheme is transferred to other subjects. We can in fact ask ourselves what would justify the extension of the scheme to other subjects and how would it be possible to explain their actions through a scheme like P–I if we could not accede the other’s world as if it were our own world. This part of the argument from contextuality will be expanded on in the second argument from the indexicality of thoughts as reasons (Stüber, 2006, p. 161 ff).

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(B) The argument from the essential indexicality of thoughts as reasons

This argument is divided into two parts. The first part of the argument can be formulated in the following way. The scheme:

1. B(x, goal p) 3 B(x, N(p ? q)) ? x makes q appears to me as explicative of the actions x does only if it appears to me as explicative of the actions I do. But it is explicative of my actions only if I understand that my belief that goal p and my belief that N(p ? q) imply my doing q. In other words, my reasons for my doing q must be ego-indexed.

2. The second part of the argument reads that when I think of goal p and N(p ? q) as reasons for others, I have to think of them as if they were my own reasons.

Analysis of and comment on the argument.

a. Our first remark is that indexicality essentially requires the first person’s perspective. However, this does not imply empathy, but only self-perception or inner perception.

b. Secondly, empathy as an ability to reenact others’ thoughts is required, if at all, in the passage from my reasons to others’ reasons. That is, it has to be introduced as early as in the second part of the argument from indexicality.

c. Thirdly, it is debatable whether reenactive empathy should be understood as a sui generis kind of knowledge. Empathy is in fact a form of knowledge which, on the one hand, is different from empirical perception, but which, on the other, is of the very same kind as perception, that is to say it is a form of perception and not a sort of pure a priori evidence. Thus it would represent a third kind of knowledge, in addition to empirical knowledge and genuinely a priori knowl- edge. The question then is whether it is strictly necessary to assume this new form of knowledge or whether it could be replaced by the synergic work of both inner perception and a priori knowledge. Empathy could be understood as an intentional capacity addressed to a ‘‘something’’ which is different from ourselves and is conceived of as a subject rather than as an object. The knowledge we suppose to have of the other could be actually interpreted in a different manner, that is, as the result of the information we derive from our capacity to represent to ourselves the other’s world and to draw from this the explanation of her behaviour. On this construal, we would be entitled to believe in the exis- tence of others’ inner worlds thanks to their capacity to explain others’ behaviours to me.

4. Conclusion

Heal’s and Stüber’s arguments in favour of the epistemic role of reenactive empathy do not appear to be conclusive. How- ever, the way the argumentation has been developed does not preclude the possibility of exploiting empirical research to ascertain whether reenactive empathy is or is not an original kind of knowledge of others’ minds. Clearly, the deployment of empirical data to deal with an epistemological problem requires a theory about the relationship between conceptual and empirical knowledge. Its function is to legitimate the contribution of the empirical data to the construction of a conceptual and apriori kind of knowledge like that supplied by philosophy. We cannot exhaustively treat this topic in the present essay, but, since MNS delivers the most influential empirical result so far about empathy, we shall deal with the issue of whether the empirical results lend some support to this philosophical account of empathy.

First, it is appropriate to stress that apriori and empirical considerations about empathy are not incompatible. In fact, the philosophical reflections provided above leave open the question about empathy. The possibility of empathy as an original kind of knowledge of other subjects’ minds has not been excluded, even though doubts have been cast on the claim that a priori reasons are sufficient for reaching a positive verdict on empathy.

However, something more than mere compatibility is needed for arguing for the relevance of MNS to the empathy issue. It is necessary that neurobiology tells us what the role of mirror neurons is in the construction of intersubjectivity and if this role supports the thesis of a capacity which cannot be explained through the perception of a purely objective phenomenon like behaviour.

We believe that the answer to the first question is quite uncontroversial. Empirical evidence shows that mirror neurons play a major role in the construction of a basic kind of relationship with the other. The answer to the second question is in- stead more thorny. It implicitly contains a hint at an impossibility proof. A theory about mirror neurons, in fact, should pro- vide an argument to the effect that mirror neurons possess a capacity for intersubjectivity that is not explainable through the mere elaboration of objective perceptive data. In other words, the theory about mirror neurons should be able to exclude the possibility that mirror neurons can perform their function without implying empathic capacities. As is known, proofs of impossibility (or of indispensability) are very difficult and, sometimes, not conclusive. An opponent of the empathy thesis based on mirror neurons could argue that she can explain the evidence of intersubjectivity in a different way, i.e. by means of evolutionary theory. The argument would go as follows. The promptness with which neurons react to others’ mental world does not depend on any specific empathic capacity, but on the fact that this circumstance expresses in an immediate and non-reflexive way the capacity that the organism has acquired in its millenary history to represent to itself others’ men- tal world on the basis of their behaviours. The mirroring capacity of mirror neurons should not then be explained empath- ically, since it can be conceived of as the result of an evolutionary application of theory–theory.

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However plausible this interpretation may appear, we think that the evolutionary way of arguing is debatable. In fact, it could be employed to all of the a priori capacities. As the evolutionary theory of knowledge affirms, these too are the result of the sedimentation of the species’ experiences in the individual. Thus, just as we believe that the evolutionary argument does not hold as regards the a priori in general, it seems to us quite wobbly also in the case of an empathic reading of mirror neurons.

To sum up, there is no question that philosophical reflection successfully argues for the validity of the first person’s per- spective, while the a priori arguments in favour of the empathy thesis remain problematic. Empirical research on MNS is surely an important clue to the validity of the empathy thesis, at least as far as empathy is conceived of as a basic capacity (on this see Corradini, 2011). Nevertheless, further work is still to be done on both sides.

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  • Mirror neurons and their function in cognitively understood empathy
    • 1 Introduction
    • 2 Empathy and MNS from the point of view of psychology and neuroscience
      • 2.1 Mirroring and mentalising mechanisms underlying empathy
      • 2.2 Mirror neurons and empathy: empirical data
      • 2.3 Mirror neurons and empathy: conceptual problems
    • 3 From mirror neurons to reenactive empathy
      • 3.1 Empathy as reenactive empathy
      • 3.2 Rational explanation
      • 3.3 Is reenactive empathy an epistemic capacity?
    • 4 Conclusion
    • References

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