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Unit 2 DB: What makes the brain “tick”?

Unit 2 DB: What makes the brain “tick”?

For this discussion, answer the following questions:

  • What are three (3) facts you learned about the brain that you didn’t know before?  Please be sure to provide examples.
  • Why do you personally think that learning more about the brain is helpful in studying psychology?  Please be sure to provide examples. 
  • If you could choose any nervous system disorder to study, which disorder would you choose, and why?  Look up three (3) facts about your chosen disorder to share with your classmates.

Be sure to provide the URL link(s) and/or title(s) to any resource used as reference in your post.

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© DGLimages/Shutterstock

CHAPTER 2

Neuroscience and Behavior

LEARNING OUTCOMES FOR CHAPTER 3

MODULE 5

NEURONS: THE BASIC ELEMENTS OF BEHAVIOR

The Structure of the Neuron

How Neurons Fire

Where Neurons Meet: Bridging the Gap

Neurotransmitters: Multitalented Chemical Couriers

LO 5-1 Why do psychologists study the brain and the nervous system?

LO 5-2 What are the basic elements of the nervous system?

LO 5-3 How does the nervous system communicate electrical and chemical messages from one part to another?

MODULE 6

THE NERVOUS SYSTEM AND THE ENDOCRINE SYSTEM: COMMUNICATING WITHIN THE BODY

The Nervous System: Linking Neurons

The Evolutionary Foundations of the Nervous System

The Endocrine System: Of Chemicals and Glands

LO 6-1 How are the structures of the nervous system linked?

LO 6-2 How does the endocrine system affect behavior?

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MODULE 7

THE BRAIN

Studying the Brain’s Structure and Functions: Spying on the Brain

Applying Psychology in the 21st Century: Bypassing Broken Neural Pathways with a Chip in the Brain

The Central Core: Our “Old Brain”

The Limbic System: Beyond the Central Core

The Cerebral Cortex: Our “New Brain”

Neuroplasticity and the Brain

Neuroscience in Your Life: The Plastic Brain

The Specialization of the Hemispheres: Two Brains or One?

Exploring Diversity: Human Diversity and the Brain

The Split Brain: Exploring the Two Hemispheres

Becoming an Informed Consumer of Psychology: Learning to Control Your Heart—and Mind—Through Biofeedback

LO 7-1 How do researchers identify the major parts and functions of the brain?

LO 7-2 What are the major parts of the brain, and for what behaviors is each part responsible?

LO 7-3 How do the halves of the brain operate interdependently?

LO 7-4 How can an understanding of the nervous system help us find ways to alleviate disease and pain?

PROLOGUE The power of thought

One rainy day Dennis Degray was taking out the trash when he slipped on a patch of wet grass and landed chin first. The fall severely injured his spinal cord, leaving Degray a quadriplegic, all communication severed between his brain and the musculature below his head.

But thanks to recent advances in brain-computer interface (BCI) research, Degray, 64, can now type about eight words a minute. That’s almost as fast as you can type a text on your cellphone. By merely visualizing his own arm, hand, and finger movements, he can control a computer cursor to spell out words.

One of three test subjects used in the pilot experiment at Stanford University, Degray had two silicon chips, each measuring 1/6-inch square, implanted in his brain. These chips record signals from the motor cortex and send them through a cable to a computer where algorithms translate them into point-and click commands (Goldman, 2017).

LOOKING Ahead

It’s hard to believe that someone can write words on a computer just by imagining the motions of their hand pressing the keys of an online keyboard. But that’s just one way neuroscience is harnessing the remarkable capacity of the brain to improve life for people who suffer severe motor impairment due to disease or injury.

An organ roughly half the size of a loaf of bread, the brain controls our physical, emotional, and intellectual behavior through every waking and sleeping moment. Our movements, thoughts, hopes, aspirations, dreams—our very awareness that we are human—all depend on the brain and the nerves that extend throughout the body, constituting the nervous system.

Because of the importance of the nervous system in controlling behavior and because humans at their most basic level are biological beings, many researchers in psychology and other fields as diverse as computer science, zoology, and medicine have made the biological underpinnings of behavior their specialty. These experts collectively are called neuroscientists (Gazzaniga, Ivry, & Mangun, 2002; Cartwright, 2006; Kasemsap, 2017).

Psychologists who specialize in considering the ways in which the biological structures and functions of the body affect behavior are known as  behavioral neuroscientists  (or biopsychologists). They seek to answer several key questions: How does the brain control the voluntary and involuntary functioning of the body? How does the brain communicate with other parts of the body? What is the physical structure of the brain, and how does this structure affect behavior? Are psychological disorders caused by biological factors, and how can such disorders be treated?

As you consider the biological processes that we discuss in this chapter, keep in mind the reason why behavioral neuroscience is an essential part of psychology: Our understanding of human behavior requires knowledge of the brain and other parts of the nervous system. Biological factors are central to our sensory experiences, states of consciousness, motivation and emotion, development throughout the life span, and physical and psychological health. Furthermore, advances in behavioral neuroscience have led to the creation of drugs and other treatments for psychological and physical disorders. In short, we cannot understand behavior without understanding our biological makeup (Plomin, 2003; Compagni & Manderscheid, 2006; Schlinger, 2015).

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Module 5 Neurons: The Basic Elements of Behavior

LEARNING OUTCOMES

LO 5-1 Why do psychologists study the brain and the nervous system?

LO 5-2 What are the basic elements of the nervous system?

LO 5-3 How does the nervous system communicate electrical and chemical messages from one part to another?

Watching Serena Williams hit a stinging backhand, Dario Vaccaro dance a complex ballet routine, or Derek Jeter swing at a baseball, you may have marveled at the complexity—and wondrous abilities—of the human body. But even the most everyday tasks, such as pouring a cup of coffee or humming a tune, depend on a sophisticated sequence of events in the body that is itself truly impressive.

The nervous system is the pathway for the instructions that permit our bodies to carry out such precise activities. Here, we look at the structure and function of neurons, the cells that make up the nervous system, including the brain.

The Structure of the Neuron

Playing the piano, driving a car, or hitting a tennis ball depends, at one level, on exact muscle coordination. But if we consider how the muscles can be activated so precisely, we see that more fundamental processes are involved. For the muscles to produce the complex movements that make up any meaningful physical activity, the brain has to provide the right messages to them and coordinate those messages.

Such messages—as well as those that enable us to think, remember, and experience emotion—are passed through specialized cells called neurons.  Neurons , or nerve cells, are the basic elements of the nervous system. Their quantity is staggering—perhaps as many as 1 trillion neurons throughout the body are involved in the control of behavior (Boahen, 2005).

Although there are several types of neurons, they all have a similar structure, as illustrated in Figure 1. Like most cells in the body, neurons have a cell body that contains  Page 48a nucleus. The nucleus incorporates the hereditary material that determines how a cell will function. Neurons are physically held in place by glial cells. Glial cells provide nourishment to neurons, insulate them, help repair damage, and generally support neural functioning (Bassotti & Villanacci, 2011; Toft et al., 2013; Keshavarz, 2017).

FIGURE 1 The primary components of the neuron, the basic element of the nervous system. A neuron has a cell body and structures that conduct messages: the dendrites, which receive messages from other neurons, and the axon, which carries messages to other neurons or body cells. As with most neurons, this axon is protected by the sausagelike myelin sheath. What advantages does the treelike structure of the neuron provide?

©McGraw-Hill Global Education Holdings LLC, 2000; (Photo): ©whitehoune/Shutterstock

In contrast to most other cells, however, neurons have a distinctive feature: the ability to communicate with other cells and transmit information across relatively long distances. Many of the body’s neurons receive signals from the environment or relay the nervous system’s messages to muscles and other target cells, but the vast majority of neurons communicate only with other neurons in the elaborate information system that regulates behavior.

As shown in Figure 1, there’s a cluster of fibers at the end of every neuron that are called dendrites.  Dendrites  are the part of the neuron that receives messages from other neurons. They look like the twisted branches of a tree.

On the opposite side of every neuron is a long, slim, tube-like extension called an axon. The  axon  carries messages received by the dendrites to other neurons. The axon is considerably longer than the rest of the neuron. Although most axons are several millimeters in length, some are as long as 3 feet. Axons end in small bulges called terminal buttons.  Terminal buttons  send messages to other neurons. They look like a small bulge at the end of the axon.

The messages that travel through a neuron are electrical in nature. Although there are exceptions, those electrical messages, or impulses, generally move across neurons in one direction only, as if they were traveling on a one-way street. Impulses follow a route that begins with the dendrites, continues into the cell body, and leads ultimately along the tube-like extension, the axon, to adjacent neurons.

Study Alert

Remember that dendrites detect messages from other neurons; axons carry signals away from the neuron.

To prevent messages from short-circuiting one another, axons must be insulated in some fashion (just as electrical wires must be insulated). Most axons are insulated by a  myelin sheath , a protective coating of fat and protein that wraps around the axon like the casing on links of sausage.

The myelin sheath also serves to increase the velocity with which electrical impulses travel through axons. Those axons that carry the most important and most urgently required information have the greatest concentrations of myelin. If your hand touches a painfully hot stove, for example, the information regarding the pain is passed through axons in the hand and arm that have a relatively thick coating of myelin, speeding the message of pain to the brain so that you can react instantly.

How Neurons Fire

Like a gun, neurons either fire—that is, transmit an electrical impulse along the axon—or don’t fire. There is no in-between stage, just as pulling harder on a gun trigger doesn’t make the bullet travel faster. Similarly, neurons follow an  all-or-none law : They are either on or off, with nothing in between the on state and the off state. When there is enough force to pull the trigger, a neuron fires.

Before a neuron is triggered—that is, when it is in a  resting state —it has a negative electrical charge of about −70 millivolts (a millivolt is one 1⁄1,000 of a volt). This charge is caused by the presence of more negatively charged ions within the neuron than outside it. (An ion is an atom that is electrically charged.) You might think of the neuron as a miniature battery in which the inside of the neuron represents the negative pole and the outside represents the positive pole.

When a message arrives at a neuron, gates along the cell membrane open briefly to allow positively charged ions to rush in at rates as high as 100 million ions per second. The sudden arrival of these positive ions causes the charge within the nearby part of the cell to change momentarily from negative to positive. When the positive charge reaches a critical level, the “trigger” is pulled, and an electrical impulse, known as an action potential, travels along the axon of the neuron (see Figure 2).

FIGURE 2 Movement of an action potential along an axon. Just before Time 1, positively charged ions enter the cell membrane, changing the charge in the nearby part of the axon from negative to positive and triggering an action potential. The action potential travels along the axon, as illustrated in the changes occurring from Time 1 to Time 3 (from top to bottom in this drawing). Immediately after the action potential has passed through a section of the axon, positive ions are pumped out, restoring the charge in that section to negative. The change in voltage illustrated by the blue line above the axon can be seen in greater detail in Figure 3.

The  action potential  moves from one end of the axon to the other like a flame moving along a fuse. As the impulse travels along the axon, the movement of ions Page 49causes a change in charge from negative to positive in successive sections of the axon (see Figure 3). After the impulse has passed through a particular section of the axon, positive ions are pumped out of that section, and its charge returns to negative while the action potential continues to move along the axon.

FIGURE 3 Changes in the voltage in a neuron during the passage of an action potential. In its normal resting state, a neuron has a negative charge of about −70 millivolts. When an action potential is triggered, however, the charge becomes positive, increasing from about −70 millivolts to about +40 millivolts. Immediately following the passage of the action potential, the charge becomes even more negative than it is in its typical resting state. After the charge returns to its normal resting state, the neuron will be fully ready to be triggered once again.

Just after an action potential has passed through a section of the axon, the cell membrane in that region cannot admit positive ions again for a few milliseconds, and  Page 50so a neuron cannot fire again immediately no matter how much stimulation it receives. It is as if the gun has to be reloaded after each shot. There then follows a period in which, though it is possible for the neuron to fire, a stronger stimulus is needed than would be if the neuron had reached its normal resting state. Eventually, though, the neuron is ready to fire again.

SPEED OF TRANSMISSION

These complex events can occur at dizzying speeds, although there is great variation among different neurons. The particular speed at which an action potential travels along an axon is determined by the axon’s size and the thickness of its myelin sheath. Axons with small diameters carry impulses at about 2 miles per hour; longer and thicker ones can average speeds of more than 225 miles per hour.

Neurons differ not only in terms of how quickly an impulse moves along the axon but also in their potential rate of firing. Some neurons are capable of firing as many as 1,000 times per second; others fire at much slower rates. The intensity of a stimulus determines how much of a neuron’s potential firing rate is reached. A strong stimulus, such as a bright light or a loud sound, leads to a higher rate of firing than a less intense stimulus does. Thus, even though all impulses move at the same strength or speed through a particular axon—because of the all-or-none law—there is variation in the frequency of impulses, providing a mechanism by which we can distinguish the tickle of a feather from the weight of someone standing on our toes.

MIRROR NEURONS

Although all neurons operate through the firing of action potentials, there is significant specialization among different types of neurons. For example, neuroscientists have discovered the existence of  mirror neurons , neurons that fire not only when a person enacts a particular behavior but also when a person simply observes another individual carrying out the same behavior (Spaulding, 2013; Brucker et al., 2015; Bonini, 2017).

Mirror neurons may help explain how (and why) humans have the capacity to understand others’ intentions. Specifically, mirror neurons may fire when we view someone doing something, helping us to predict what their goals are and what they may do next.

The discovery of mirror neurons suggests that the capacity of even young children to imitate others may be an inborn behavior. Furthermore, mirror neurons may be at the root of empathy—those feelings of concern, compassion, and sympathy for others—and even the development of language in humans (Ramachandra, 2009; Rogalsky et al., 2011; Lim & Okuno, 2015).

Some researchers suggest an even broader role for mirror neurons. For example, mirror neurons, which respond to sound, appear to be related to speech perception and language comprehension. Furthermore, stimulating the mirror neuron system can help stroke victims as well and may prove to be helpful for those with emotional problems by helping them to develop greater empathy (Gallese et al., 2011; Hoenen, Lübke, & Pause, 2017).

Where Neurons Meet: Bridging the Gap

If you have looked inside a computer, you’ve seen that each part is physically connected to another part. In contrast, evolution has produced a neural transmission system that at some points has no need for a structural connection between its components. Instead, a chemical connection bridges the gap, known as a synapse, between two neurons (see Figure 4). The  synapse  is the space between two neurons where the axon of a sending neuron communicates with the dendrites of a receiving neuron by using chemical messages.

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FIGURE 4 A synapse is the junction between an axon and a dendrite. Chemical neurotransmitters bridge the synaptic gap between the axon and the dendrite (Mader, 2000). (a) Read Step 1 through Step 4 to follow this chemical process. (b) Just as the pieces of a jigsaw puzzle can fit in only one specific location in a puzzle, each kind of neurotransmitter has a distinctive configuration that allows it to fit into a specific type of receptor cell (Johnson, 2000). Why is it advantageous for axons and dendrites to be linked by temporary chemical bridges rather than by the hard wiring typical of a radio connection or telephone hookup?

(a and b): ©McGraw-Hill Global Education Holdings LLC, 2000.

When a nerve impulse comes to the end of the axon and reaches a terminal button, the terminal button releases a chemical messenger called a neurotransmitter.  Neurotransmitters  carry messages from one neuron to another neuron. Like a boat that ferries passengers across a river, these chemical messengers move from the axon of one neuron to the dendrite of a receiving neurons.

Keep in mind that the chemical mode of message transmission that occurs between neurons differs strikingly from the means by which communication occurs inside neurons: Although messages travel in electrical form within a neuron, they move between neurons through a chemical transmission system.

There are several types of neurotransmitters, and not all neurons are capable of receiving the chemical message carried by a particular neurotransmitter. In the same way that a jigsaw puzzle piece can fit in only one specific location in a puzzle, each kind of neurotransmitter has a distinctive configuration that allows it to fit into a specific type of receptor site on the receiving neuron (see Figure 4b). It is only when a neurotransmitter fits precisely into a receptor site that successful chemical communication is possible.

Study Alert

Remember this key fact: Messages inside neurons are transmitted in electrical form, whereas messages traveling between neurons travel via chemical means.

If a neurotransmitter does fit into a site on the receiving neuron, the chemical message it delivers is basically one of two types: excitatory or inhibitory.  Excitatory messages  are chemical messages that make it more likely that a receiving neuron will fire and an action potential will travel down its axon. In contrast, inhibitory messages do just the opposite:  inhibitory messages  provide chemical information that prevents or decreases the likelihood that the receiving neuron will fire.

Because the dendrites of a neuron receive both excitatory and inhibitory messages simultaneously, the neuron must integrate the messages by using a kind of chemical calculator. Put simply, if the excitatory messages (“Fire!”) outnumber the inhibitory ones (“Don’t fire!”), the neuron fires. In contrast, if the inhibitory messages outnumber the excitatory ones, nothing happens, and the neuron remains in its resting state.

If neurotransmitters remained at the site of the synapse, receiving neurons would be awash in a continual chemical bath, producing constant stimulation or constant inhibition of the receiving neurons. This would make effective communication across the synapse impossible. To avoid this problem, enzymes deactivate the neurotransmitters, or—more commonly—the terminal button sucks them back up in an example of chemical recycling called reuptake.

Reuptake  is the process in which a neurotransmitter produced by a terminal button is reabsorbed by the terminal button. Like a vacuum cleaner sucking up dust, neurons reabsorb the neurotransmitters that are now clogging the synapse. All this activity occurs at lightning speed, with the process taking just several milliseconds (Gingrich et al., 2017).

Our understanding of the process of reuptake has permitted the development of a number of drugs used in the treatment of psychological disorders. Some antidepressant drugs, called SSRIs, or selective serotonin reuptake inhibitors, permit certain neurotransmitters to remain active for a longer period at certain synapses in the brain, thereby reducing the symptoms of depression (Guiard et al., 2011; Hilton et al., 2013; Leong et al., 2017).

Neurotransmitters: Multitalented Chemical Couriers

Neurotransmitters are a particularly important link between the nervous system and behavior. Not only are they important for maintaining vital brain and body functions, but a deficiency or an excess of a neurotransmitter can produce severe behavior disorders. More than a hundred chemicals have been found to act as neurotransmitters, and neuroscientists believe that more may ultimately be identified. The major neurotransmitters and their effects are described in Figure 5 (Schmidt, 2006).

FIGURE 5 Major neurotransmitters.

One of the most common neurotransmitters is acetylcholine (or ACh, its chemical symbol), which is found throughout the nervous system. ACh is involved in our every physical move because—among other things—it transmits messages relating to our skeletal muscles. ACh also aids in memory capabilities. In fact, diminished production of ACh may be related to Alzheimer’s disease (Bazalakova et al., 2007; Van der Zee, Platt, & Riedel, 2011; Betterton et al., 2017).

Another common excitatory neurotransmitter, glutamate, plays a role in memory. Memories appear to be produced by specific biochemical changes at particular synapses, and glutamate, along with other neurotransmitters, plays an important role in this process (Winters & Bussey, 2005; Micheau & Marighetto, 2011; Solomonia & McCabe, 2015).

Gamma-amino butyric acid (GABA), which is found in both the brain and the spinal cord, appears to be the nervous system’s primary inhibitory neurotransmitter. It moderates a variety of behaviors, ranging from eating to aggression. Several common substances, such as the tranquilizer Valium and alcohol, are effective because they permit GABA to operate more efficiently (Ball, 2004; Criswell et al., 2008; Lobo & Harris, 2008).

Michael J. Fox suffers from Parkinson’s disease, and he has become a strong advocate for research into the disorder.

© Theo Wargo/Getty Images

Another major neurotransmitter is dopamine (DA), which is involved in movement, attention, and learning. The discovery that certain drugs can have a significant effect on dopamine release has led to the development of effective treatments for a wide variety of physical and mental ailments. For instance, Parkinson’s disease, from which actor Michael J. Fox suffers, is caused by a deficiency of dopamine in the brain. Techniques for increasing the production of dopamine in Parkinson’s patients are proving effective (Iversen & Iversen, 2007; Antonini & Barone, 2008; Hanna-Pladdy, Pahwa, & Lyons, 2015).

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PsychTech

A team of Swedish researchers has discovered a way to stimulate specific neurons via chemical neurotransmitters, rather than using earlier technologies involving electrical signals to stimulate them. This discovery opens a novel path to treat those who suffer from severe psychological disorders produced by brain dysfunction.

In other instances, overproduction of dopamine produces negative consequences. For example, researchers have hypothesized that schizophrenia and some other severe mental disturbances are affected or perhaps even caused by the presence of unusually high levels of dopamine. Drugs that block the reception of dopamine reduce the symptoms displayed by some people diagnosed with schizophrenia (Howes & Kapur, 2009; Seeman, 2011; Howes et al., 2017).

From the perspective of …

© Tetra Images/Getty Images

A Health-Care Provider How might your understanding of the nervous system help you explain the symptoms of Parkinson’s disease to a patient with the disorder?

Another neurotransmitter, serotonin, is associated with the regulation of sleep, eating, mood, and pain. A growing body of research points toward a broader role for serotonin, suggesting its involvement in such diverse behaviors as alcoholism, depression, suicide, impulsivity, aggression, and coping with stress (Murray et al., 2008; Popa et al., 2008; Carrillo et al., 2009).

Endorphins, another class of neurotransmitters, are a family of chemicals produced by the brain that are similar in structure to painkilling drugs such as morphine. The production of endorphins reflects the brain’s effort to deal with pain as well as to elevate mood.

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Endorphins also may produce the euphoric feelings that runners sometimes experience after long runs. The exertion and perhaps the pain involved in a long run may stimulate the production of endorphins, ultimately resulting in what has been called “runner’s high” (Kolata, 2002; Pert, 2002; Stanojevic, Mitic, & Vujic, 2007).

Endorphin release might also explain other phenomena that have long puzzled psychologists. For example, the act of taking placebos (pills or other substances that contain no actual drugs but that patients believe will make them better) may induce the release of endorphins, leading to the reduction of pain (Rajagopal, 2006; Crum & Langer, 2007; Bruehl et al., 2017).

RECAP/EVALUATE/RETHINK

RECAP

LO 5-1 Why do psychologists study the brain and nervous system?

•A full understanding of human behavior requires knowledge of the biological influences underlying that behavior, especially those originating in the nervous system. Psychologists who specialize in studying the effects of biological structures and functions on behavior are known as behavioral neuroscientists.

LO 5-2 What are the basic elements of the nervous system?

•Neurons, the most basic elements of the nervous system, carry nerve impulses from one part of the body to another. Information in a neuron generally follows a route that begins with the dendrites, continues into the cell body, and leads ultimately down the tube-like extension, the axon.

LO 5-3 How does the nervous system communicate electrical and chemical messages from one part to another?

•Most axons are insulated by a coating called the myelin sheath. When a neuron receives a message to fire, it releases an action potential, an electric charge that travels through the axon. Neurons operate according to an all-or-none law: Either they are at rest, or an action potential is moving through them. There is no in-between state.

•When a neuron fires, nerve impulses are carried to other neurons through the production of chemical substances called neurotransmitters that bridge the gaps—known as synapses—between neurons. Neurotransmitters may be either excitatory, telling other neurons to fire, or inhibitory, preventing or decreasing the likelihood of other neurons firing.

•Endorphins, another type of neurotransmitter, are related to the reduction of pain. Endorphins aid in the production of a natural painkiller and are probably responsible for creating the kind of euphoria that joggers sometimes experience after running.

EVALUATE

1.The __________is the fundamental element of the nervous system.

2.Neurons receive information through their __________and send messages through their __________.

3.Just as electrical wires have an outer coating, axons are insulated by a coating called the ____________________.

4.The gap between two neurons is bridged by a chemical connection called a __________.

5.Endorphins are one kind of __________, the chemical “messengers” between neurons.

RETHINK

1.How might psychologists use drugs that mimic the effects of neurotransmitters to treat psychological disorders?

2.In what ways might endorphins help to produce the placebo effect? Is there a difference between believing that one’s pain is reduced and actually experiencing reduced pain? Why or why not?

Answers to Evaluate Questions

1. neuron; 2. dendrites, axons; 3. myelin sheath; 4. synapse; 5. neurotransmitter

KEY TERMS

behavioral neuroscientists (or biopsychologists)

neurons

dendrite

axon

terminal buttons

myelin sheath

all-or-none law

resting state

action potential

mirror neurons

synapse

neurotransmitters

excitatory message

inhibitory message

reuptake

Module 6 The Nervous System and the Endocrine System: Communicating Within the Body

LEARNING OUTCOMES

LO 6-1 How are the structures of the nervous system linked?

LO 6-2 How does the endocrine system affect behavior?

In light of the complexity of individual neurons and the neurotransmission process, it should come as no surprise that the connections and structures formed by the neurons are complicated. Because each neuron can be connected to 80,000 other neurons, the total number of possible connections is astonishing. For instance, estimates of the number of neural connections within the brain fall in the neighborhood of 10 quadrillion—a 1 followed by 16 zeros—and some experts put the number even higher. However, connections among neurons are not the only means of communication within the body; as we’ll see, the endocrine system, which secretes chemical messages that circulate through the blood, also communicates messages that influence behavior and many aspects of biological functioning (Boahen, 2005; Heintz, Brander, & White, 2015).

The Nervous System: Linking Neurons

Whatever the actual number of neural connections, the human nervous system has both logic and elegance. We turn now to a discussion of its basic structures.

CENTRAL AND PERIPHERAL NERVOUS SYSTEMS

As you can see from the schematic representation in Figure 1, the nervous system is divided into two main parts: the central nervous system and the peripheral nervous system. The  central nervous system (CNS)  is composed of the brain and spinal cord. The  spinal cord , which is about the thickness of a pencil, contains a bundle of neurons that leaves the brain and runs down the length of the back (see Figure 2). As you can see in Figure 2, the spinal cord is the primary means for transmitting messages between the brain and the rest of the body.

FIGURE 1 A schematic diagram of the relationship of the parts of the nervous system.

FIGURE 2 The central nervous system consists of the brain and spinal cord, and the peripheral nervous system encompasses the network of nerves connecting the brain and spinal cord to other parts of the body.

©Larry Williams/Blend Images/Corbis

However, the spinal cord is not just a communication channel. It also controls some simple behaviors on its own, without any help from the brain. An example is the way the knee jerks forward when it is tapped with a rubber hammer. This behavior is a type of  reflex , an automatic, involuntary response to an incoming stimulus. A reflex is also at work when you touch a hot stove and immediately withdraw your hand. Although the brain eventually analyzes and reacts to the situation (“Ouch—hot stove—pull away!”), the initial withdrawal is directed only by neurons in the spinal cord.

Several kinds of neurons are involved in reflexes.  Sensory (afferent) neurons  transmit information from the perimeter of the body to the central nervous system and the brain. For example, touching a hot stove sends a message to the brain (hot!) via sensory neurons.  Motor (efferent) neurons  communicate information in the opposite direction, sending messages from the brain and nervous system to the muscles Page 56and glands. When the brain sends a message to the muscles of the hand (hot—move away!), the message travels via motor neurons.

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Study Alert

Use Figures 1 and 2 to learn the components of the central and peripheral nervous systems.

The importance of the spinal cord and reflexes is illustrated by the outcome of accidents in which the cord is injured or severed. In some cases, injury results in quadriplegia, a condition in which people lose voluntary muscle movement below the neck. In a less severe but still disabling condition, paraplegia, people are unable to voluntarily move any muscles in the lower half of the body.

As suggested by its name, the  peripheral nervous system  branches out from the spinal cord and brain and reaches the extremities of the body. Made up of neurons with long axons and dendrites, the peripheral nervous system encompasses all the parts of the nervous system other than the brain and spinal cord. There are two major divisions of the peripheral nervous system—the somatic division and the autonomic division—both of which connect the central nervous system with the sense organs, muscles, glands, and other organs.

The  somatic division  of the peripheral nervous system specializes in the control of voluntary movements, such as the motion of the eyes to read this sentence or those of the hand to scroll down a page. The somatic division also communicates information to and from the sense organs.

The  autonomic division  of the peripheral nervous system controls the parts of the body that keep us alive—the heart, blood vessels, glands, lungs, and other organs that function involuntarily without our awareness. As you are reading at this moment, the autonomic division of the peripheral nervous system is pumping blood through your body, pushing your lungs in and out, and overseeing the digestion of your last meal.

ACTIVATING THE DIVISIONS OF THE AUTONOMIC NERVOUS SYSTEM

The autonomic division plays a particularly crucial role during emergencies. Suppose that as you are reading, you suddenly sense that a stranger is watching you through the window. As you look up, you see the glint of something that might be a knife. As confusion clouds your mind and fear overcomes your attempts to think rationally, what happens to your body? If you are like most people, you react immediately on a physiological level. Your heart rate increases, you begin to sweat, and you develop goose bumps all over your body.

The physiological changes that occur during a crisis result from the activation of one of the two parts of the autonomic nervous system: the  sympathetic division . The sympathetic division acts to prepare the body for action in stressful situations by engaging all of the organism’s resources to run away or to confront the threat. This is often called the “fight-or-flight” response.

In contrast, the  parasympathetic division  acts to calm the body after the emergency has ended. When you find, for instance, that the stranger at the window is actually your roommate, who has lost his keys and is climbing in the window to avoid waking you, your parasympathetic division begins to take over, lowering your heart rate, stopping your sweating, and returning your body to the state it was in before you became alarmed. The parasympathetic division also directs the body to store energy for use in emergencies.

The sympathetic and parasympathetic divisions work together to regulate many functions of the body (see Figure 3). For instance, sexual arousal is controlled by the parasympathetic division, but sexual orgasm is a function of the sympathetic division. The sympathetic and parasympathetic divisions also are involved in a number of disorders. For example, one explanation of documented examples of “voodoo death”—in which a person is literally scared to death resulting from a voodoo curse—may be produced by overstimulation of the sympathetic division due to extreme fear. The Evolutionary Foundations of the Nervous System

The complexities of the nervous system can be better understood if we take the course of evolution into consideration. The forerunner of the human nervous system is found in the earliest simple organisms to have a spinal cord. Basically, those organisms were simple input-output devices: When the upper side of the spinal cord was stimulated by, for instance, being touched, the organism reacted with a simple response, such as jerking away. Such responses were completely a consequence of the organism’s genetic makeup.

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Over millions of years, the spinal cord became more specialized, and organisms became capable of distinguishing between different kinds of stimuli and responding appropriately to them. Ultimately, a portion of the spinal cord evolved into what we would consider a primitive brain.

Today, the nervous system is hierarchically organized, meaning that relatively newer (from an evolutionary point of view) and more sophisticated regions of the brain regulate the older, and more primitive, parts of the nervous system. As we move up along the spinal cord and continue upward into the brain then, the functions controlled by the various regions become progressively more advanced.

Why should we care about the evolutionary background of the human nervous system? The answer comes from researchers working in the area of  evolutionary psychology , the branch of psychology that seeks to identify how behavior is influenced and produced by our genetic inheritance from our ancestors.

Evolutionary psychologists argue that the course of evolution is reflected in the structure and functioning of the nervous system and that evolutionary factors consequently have a significant influence on our everyday behavior. Their work, in conjunction with the research of scientists studying genetics, biochemistry, and medicine, has led to an understanding of how our behavior is affected by heredity, our genetically determined heritage.

Evolutionary psychologists have spawned a new and increasingly influential field: behavioral genetics. As we will discuss further in the chapter on development,  behavioral genetics  is the study of the effects of heredity on behavior. Consistent with the evolutionary perspective, behavioral genetics researchers are finding increasing evidence that cognitive abilities, personality traits, sexual orientation, and psychological disorders are determined to some extent by genetic factors (Maxson, 2013; Appelbaum, Scurich, & Raad, 2015; Barbaro et al., 2017).

The Endocrine System: Of Chemicals and Glands

Another of the body’s communication systems, the  endocrine system  is a chemical communication network that sends messages throughout the body via the bloodstream. Its job is to secrete  hormones , chemicals that circulate through the blood and regulate the functioning or growth of the body. It also influences—and is influenced by—the functioning of the nervous system. Although the endocrine system is not part of the brain, it is closely linked to the hypothalamus.

As chemical messengers, hormones are like neurotransmitters, although their speed and mode of transmission are quite different. Whereas neural messages are measured in thousandths of a second, hormonal communications may take minutes to reach their destination. Furthermore, neural messages move through neurons in specific lines (like a signal carried by wires strung along telephone poles), whereas hormones travel throughout the body, similar to the way radio waves are transmitted across the entire landscape. Just as radio waves evoke a response only when a radio is tuned to the correct station, hormones flowing through the bloodstream activate only those cells that are receptive and “tuned” to the appropriate hormonal message.

A key component of the endocrine system is the tiny  pituitary gland , which is found near—and regulated by—the hypothalamus in the brain. The pituitary gland has sometimes been called the “master gland” because it controls the functioning of the rest of the endocrine system. But the pituitary gland is more than just the taskmaster of other glands; it has important functions in its own right. For instance, hormones secreted by the pituitary gland control growth. Extremely short people and unusually tall ones usually have pituitary gland abnormalities. Other endocrine glands, shown in Figure 4, affect emotional reactions, sexual urges, and energy levels.

FIGURE 4 Location and function of the major endocrine glands. The pituitary gland controls the functioning of the other endocrine glands and, in turn, is regulated by the hypothalamus.

©Laurence Mouton/Getty Images

Study Alert

The endocrine system produces hormones, chemicals that circulate through the body via the bloodstream.

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Despite its designation as the “master gland,” the pituitary is actually a servant of the brain because the brain is ultimately responsible for the endocrine system’s functioning. The brain maintains the internal balance of the body through the hypothalamus.

Individual hormones can wear many hats, depending on circumstances. For example, the hormone oxytocin is at the root of many of life’s satisfactions and pleasures. In new mothers, oxytocin produces an urge to nurse newborn offspring. The same hormone also seems to stimulate cuddling between species members. And—at least in rats—it encourages sexually active males to seek out females more passionately and females to be more receptive to males’ sexual advances. There’s even evidence that oxytocin is related to the development of trust in others, helping to grease the wheels of effective social interaction (Guastella, Mitchell, & Dadds, 2008; De Dreu et al., 2011; de Visser et al., 2017).

Although hormones are produced naturally by the endocrine system, the ingestion of artificial hormones has proved to be both beneficial and potentially dangerous. For example, before the early 2000s, physicians frequently prescribed hormone replacement therapy to treat symptoms of menopause in older women. However, because recent research suggests that the treatment has potentially dangerous side effects, health experts now warn that in many cases, the dangers outweigh the benefits (Alexandersen, Karsdal, & Christiansen, 2009; Jacobs et al., 2013; Doty et al., 2015).

The use of testosterone, a male hormone, and drugs known as steroids, which act like testosterone, is increasingly common. For athletes and others who want to bulk up their appearance, steroids provide a way to add muscle weight and increase strength. 

The use of testosterone, a male hormone, and drugs known as steroids, which act like testosterone, is increasingly common. For athletes and others who want to bulk up their appearance, steroids provide a way to add muscle weight and increase strength. Page 61However, these drugs can lead to stunted growth, shrinking of the testicles, heart attacks, strokes, and cancer, making them extremely dangerous. Furthermore, they can even produce violent behavior. For example, in one tragic case, professional wrestler Chris Benoit strangled his wife, suffocated his son, and later hanged himself—acts that were attributed to his use of steroids (Pagonis, Angelopoulos, & Koukoulis, 2006; Sandomir, 2007; Zahnow et al., 2017).

Steroids can provide added muscle and strength, but they have dangerous side effects. A number of well-known athletes in a variety of sports, such as baseball player Alex Rodriguez, pictured here, have been accused of using the drugs illegally. In fact, a number of them have publicly said they have used them.

© Corey Sipkin/NY Daily News Archive/Getty Images

RECAP/EVALUATE/RETHINK

RECAP

LO 6-1 How are the structures of the nervous system linked?

•The nervous system is made up of the central nervous system (the brain and spinal cord) and the peripheral nervous system. The peripheral nervous system is made up of the somatic division, which controls voluntary movements and the communication of information to and from the sense organs, and the autonomic division, which controls involuntary functions such as those of the heart, blood vessels, and lungs.

•The autonomic division of the peripheral nervous system is further subdivided into the sympathetic and parasympathetic divisions. The sympathetic division prepares the body in emergency situations, and the parasympathetic division helps the body return to its typical resting state.

•Evolutionary psychology, the branch of psychology that seeks to identify behavior patterns that are a result of our genetic inheritance, has led to increased understanding of the evolutionary basis of the structure and organization of the human nervous system.

LO 6-2 How does the endocrine system affect behavior?

•The endocrine system secretes hormones, chemicals that regulate the functioning of the body, via the bloodstream. The pituitary gland secretes growth hormones and influences the release of hormones by other endocrine glands and in turn is regulated by the hypothalamus.

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EVALUATE

1.If you put your hand on a red-hot piece of metal, the immediate response of pulling it away would be an example of a(n) __________.

2.The central nervous system is composed of the __________and the __________.

3.In the peripheral nervous system, the __________division controls voluntary movements, whereas the __________division controls organs that keep us alive and function without our awareness.

4.Maria saw a young boy run into the street and get hit by a car. When she got to the fallen child, she was in a state of panic. She was sweating, and her heart was racing. Her biological state resulted from the activation of what division of the nervous system?

a.parasympathetic

b.central

c.sympathetic

5.The emerging field of __________studies ways in which our genetic inheritance predisposes us to behave in certain ways.

RETHINK

1.In what ways is the “fight-or-flight” response helpful to humans in emergency situations?

2.How might communication within the nervous system result in human consciousness?

Answers to Evaluate Questions

1. reflex; 2. brain, spinal cord; 3. somatic, autonomic; 4. c. sympathetic; 5. evolutionary psychology

KEY TERMS

central nervous system (CNS)

spinal cord

reflex

sensory (afferent) neurons

motor (efferent) neurons

peripheral nervous system

somatic division

autonomic division

sympathetic division

parasympathetic division

evolutionary psychology

behavioral genetics

endocrine system

hormones

pituitary gland

Module 7 The Brain

LEARNING OUTCOMES

LO 7-1 How do researchers identify the major parts and functions of the brain?

LO 7-2 What are the major parts of the brain, and for what behaviors is each part responsible?

LO 7-3 How do the two halves of the brain operate interdependently?

LO 7-4 How can an understanding of the nervous system help us find ways to alleviate disease and pain?

It is not much to look at. Soft, spongy, mottled, and pinkish-gray in color, it hardly can be said to possess much in the way of physical beauty. Despite its physical appearance, however, it ranks as the greatest natural marvel that we know and has a beauty and sophistication all its own.

The object to which this description applies: the brain. The brain is responsible for our loftiest thoughts—and our most primitive urges. It is the overseer of the intricate workings of the human body. If one were to attempt to design a computer to mimic the range of capabilities of the brain, the task would be nearly impossible; in fact, it has proved difficult even to come close. The sheer quantity of nerve cells in the brain is enough to daunt even the most ambitious computer engineer. Many billions of neurons make up a structure weighing just 3 pounds in the average adult. However, it is not the number of cells that is the most astounding thing about the brain but its ability to allow the human intellect to flourish by guiding our behavior and thoughts.

We turn now to a consideration of the particular structures of the brain and the primary functions to which they are related. However, a caution is in order. Although we’ll discuss specific areas of the brain in relation to specific behaviors, this approach is an oversimplification. No straightforward one-to-one correspondence exists between a distinct part of the brain and a particular behavior. Instead, behavior is produced by complex interconnections among sets of neurons in many areas of the brain: Our behavior, emotions, thoughts, hopes, and dreams are produced by a variety of neurons throughout the nervous system working in concert.

Studying the Brain’s Structure and Functions: Spying on the Brain

The brain has posed a continual challenge to those who would study it. For most of history, its examination was possible only after an individual had died. Only then could the skull be opened and the brain cut into without serious injury. Although informative, this procedure could hardly tell us much about the functioning of the healthy brain.

Today, however, brain-scanning techniques provide a window into the living brain. Using these techniques, investigators can take a “snapshot” of the internal workings of the brain without having to cut open a person’s skull. The most important scanning techniques, illustrated in Figure 1, are the electroencephalogram (EEG), positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation imaging (TMS).

FIGURE 1 Brain scans produced by different techniques. (a) A computer-produced EEG image. (b) The fMRI scan uses a magnetic field to provide a detailed view of brain activity on a moment-by-moment basis. (c) The PET scan displays the functioning of the brain at a given moment. (d) Transcranial magnetic stimulation (TMS), the newest type of scan, produces a momentary disruption in an area of the brain, allowing researchers to see what activities are controlled by that area. TMS also has the potential to treat some psychological disorders.

(a) ©SPL/Science Source; (b) ©Steger Photo/Photolibrary/Getty Images; (c) ©Science History Images/Alamy Stock Photo; (d) ©Garo/Phanie/Science Source

The brain (shown here in cross-section) may not be much to look at, but it represents one of the great marvels of human development. Why do most scientists believe that it will be difficult, if not impossible, to duplicate the brain’s abilities?

© Martin M. Rotker/Science Source

The electroencephalogram (EEG) records electrical activity in the brain through electrodes placed on the outside of the skull. Although traditionally the EEG could produce only a graph of electrical wave patterns, new techniques are now used to transform the brain’s electrical activity into a pictorial representation of the brain that allows more precise diagnosis of disorders such as epilepsy and learning disabilities.

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Study Alert

Remember how EEG, fMRI, PET, and TMS scans differ in the ways that they produce an image of the brain.

Functional magnetic resonance imaging (fMRI) scans provide a detailed, three-dimensional computer-generated image of brain structures and activity by aiming a powerful magnetic field at the body. With fMRI scanning, it is possible to produce vivid, detailed images of the functioning of the brain.

Using fMRI scans, researchers are able to view features of less than a millimeter in size and view changes occurring in intervals of 1/10 of a second. For example, fMRI scans can show the operation of individual bundles of nerves by tracing the flow of blood, opening the way for improved diagnosis of ailments ranging from chronic back pain to nervous system disorders such as strokes, multiple sclerosis, and Alzheimer’s. Scans using fMRI are routinely used in planning brain surgery because they can help surgeons distinguish areas of the brain involved in normal and disturbed functioning (Loitfelder et al., 2011; Hurschler et al., 2015).

Positron emission tomography (PET) scans show biochemical activity within the brain at a given moment. PET scans begin with the injection of a radioactive (but safe) liquid into the bloodstream, which makes its way to the brain. By locating radiation within the brain, a computer can determine which are the more active regions, providing a striking picture of the brain at work. For example, PET scans may be used in cases of memory problems, seeking to identify the presence of brain tumors (Gronholm et al., 2005; McMurtray et al., 2007).

Transcranial magnetic stimulation (TMS) uses magnetic fields to produce an understanding of the functioning of the brain. In TMS, a tiny region of the brain is bombarded by a strong magnetic field that causes a momentary interruption of electrical activity. Researchers then are able to note the effects of this interruption on normal brain functioning.

One of the newest procedures used to study the brain, TMS is sometimes called a “virtual lesion” because it produces effects similar to what would occur if areas of the brain were physically cut. The enormous advantage of TMS, of course, is that the virtual cut is only temporary. In addition to identifying areas of the brain that are Page 65responsible for particular functions, TMS has the potential to treat certain kinds of psychological disorders, such as depression and schizophrenia, by shooting brief magnetic pulses through the brain (Pallanti & Bernardi, 2009; Prasser et al., 2015).

Future discoveries may yield even more sophisticated methods of examining the brain. For example, the emerging field of optogenetics involves genetic engineering and the use of special types of light to view individual circuits of neurons. In addition, researchers are developing hydrogel-embedding methods. which allow observation of individual brain cells and the wiring of brain circuitry (Deisseroth, 2016; Shirai & Hayashi-Takagi, 2017; Yang, Song, & Qing, 2017).

Advances in our understanding of the brain also are paving the way for the development of new methods for harnessing the brain’s neural signals. We consider some of these intriguing findings in Applying Psychology in the 21st Century.

APPLYING PSYCHOLOGY IN THE 21ST CENTURY

BYPASSING BROKEN NEURAL PATHWAYS WITH A CHIP IN THE BRAIN

Ian Burkhart was a typical college freshman who was just enjoying a fun, leisurely day with his family at a beach in North Carolina when his whole life changed forever. Ian jumped headfirst into an approaching wave and struck his head on the soft sand of the ocean floor, breaking his neck. From that moment on, Ian permanently lost the feeling and movement in his hands, legs, and feet. He would never walk again or be able to complete even the simplest task with his hands, such as buttoning his shirt or stirring his coffee (Carey, 2016).

But advancements in neural engineering gave Ian a seemingly miraculous opportunity to use his hands again, albeit only for a limited time. To begin, in a delicate brain surgery, doctors implanted a chip in Ian’s skull that comprises many tiny electrodes. Each electrode can detect the firing of an individual neuron within a very specific region of Ian’s motor cortex—the region responsible for hand movements. Doctors identified this region with brain imaging before the surgery and then further refined their placement of the electrodes during the surgery to isolate nearly 100 specific neurons. The chip sends signals to a port in Ian’s skull, which can be connected to computer equipment in the researchers’ lab (Bouton et al., 2016).

After Ian healed from the surgery, the next step was to train both Ian and the computer software. Ian spent many hours watching video simulations of specific hand and finger movements. As Ian watched, he was instructed to imagine himself making those movements. The neurons in his motor cortex responsible for hand movement would fire, attempting to send a signal to Ian’s paralyzed hand to move in the way Ian was imagining. Computer software read and analyzed the specific pattern of firing in the neurons monitored by the chip in Ian’s skull, learning what patterns corresponded to specific movements. The computer then sent instructions to a device attached to Ian’s forearm that could stimulate specific muscles controlling Ian’s hand and fingers. So instead of the signal being sent directly from Ian’s brain to his hand via motor pathways in the spinal cord, as would happen in a nonparalyzed person, the signal was instead being relayed from the brain to the muscles by an external computer. In this way, the technology bypassed the blockage caused by Ian’s damaged spinal cord.

©Lee Powell/The Washington Post via Getty Images

It took a great deal of effort and months of training, but Ian first regained the ability to close and open his hand just by thinking about it. Eventually, he became able to grasp and lift items with his whole hand and with his fingers, allowing him to lift and pour from a bottle and then pick up a small stirrer and use it. He even learned to manipulate a video game controller. Such reanimation, as it’s called, of a paralyzed limb was until recently the stuff of science fiction only. It became a reality for Ian, who is the first person to successfully control his muscles using his own neural signals relayed by computer.

Sadly, the success Ian experienced in the lab will not reverse his paralysis or help him function better in real life. The neural bypass only works when connected to bulky computers and other devices in the researchers’ lab, which are not portable at all. At the conclusion of the research, Ian returned to his new normal life of dependence on others for care. Still, the research represented a major advancement toward a day when such technology could be put to more practical use, and Ian is gratified to have played a part in bringing a successful treatment for paralysis one step closer to fruition (Bouton et al., 2016).

RETHINK

•Why do you think Ian volunteered to undergo brain surgery and put in many months of hard work to help develop a technology that he knew would not benefit him?

•How would you explain this research on limb reanimation to a friend who recently became paralyzed?

The Central Core: Our “Old Brain”

Although the capabilities of the human brain far exceed those of the brain of any other species, humans share some basic functions, such as breathing, eating, and sleeping, with more primitive animals. Not surprisingly, those activities are directed by a relatively primitive part of the brain. A portion of the brain known as the  central core  (see Figure 2) is quite similar in all vertebrates (species with backbones). The central core is sometimes referred to as the “old brain” because its evolution can be traced back some 500 million years to primitive structures found in nonhuman species.

FIGURE 2 The major divisions of the brain: the cerebral cortex and the central core.

©McGraw-Hill Global Education Holdings LLC, 2000.

If we were to move up the spinal cord from the base of the skull to locate the structures of the central core of the brain, the first part we would come to would be the hindbrain, which contains the medulla, pons, and cerebellum (see Figure 3). The medulla controls a number of critical body functions, the most important of which are breathing and heartbeat. The pons is a bridge in the hindbrain. Containing large bundles of nerves, the pons acts as a transmitter of motor information, coordinating muscles and integrating movement between the right and left halves of the body. It is also involved in regulating sleep.

FIGURE 3 The major structures in the brain.

Source: Adapted from Bloom, F. (1975). Brain, mind, and behavior, New York: Educational Broadcasting Corp.; (Photo): ©Dana Neely/Taxi/Getty Images

The  cerebellum  extends from the rear of the hindbrain. Without the help of the cerebellum, we would be unable to walk a straight line without staggering and lurching forward, for it is the job of the cerebellum to control bodily balance. It constantly monitors feedback from the muscles to coordinate their placement, movement, and tension. In fact, drinking too much alcohol seems to depress the activity of the cerebellum, leading to the unsteady gait and movement characteristic of drunkenness. The cerebellum is also involved in several intellectual functions, ranging from the analysis and coordination of sensory information to problem solving (Vandervert, Schimpf, & Liu, 2007; Swain, Kerr, & Thompson, 2011; Ronconi et al., 2017).

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The  reticular formation  is a nerve network in the brain that extends from the medulla through the pons, passing through the middle section of the brain, called the midbrain, and into the front-most part of the brain, called the forebrain. Like an ever-vigilant guard, the reticular formation produces general arousal of our body. If, for example, we are startled by a loud noise, the reticular formation can prompt a heightened state of awareness to determine whether a response is necessary. The reticular formation also helps regulate our sleep-wake cycle by filtering out background stimuli to allow us to sleep undisturbed.

The  thalamus , which is hidden within the forebrain, acts primarily as a relay station for information about the senses. Messages from the eyes, ears, and skin travel to the thalamus to be communicated upward to higher parts of the brain. The thalamus also integrates information from higher parts of the brain, sorting it out so that it can be sent to the cerebellum and medulla.

The  hypothalamus  is located just below the thalamus. Although tiny—about the size of a fingertip—the hypothalamus plays an extremely important role. One of its major functions is to maintain homeostasis, a steady internal environment for the body. The hypothalamus helps provide a constant body temperature and monitors the amount of nutrients stored in the cells. A second major function is equally important: the hypothalamus produces and regulates behavior that is critical to the basic survival of the species, such as eating, self-protection, and sex.

The Limbic System: Beyond the Central Core

In an eerie view of the future, science fiction writers have suggested that people someday will routinely have electrodes implanted in their brains. Those electrodes will permit them to receive tiny shocks that will produce the sensation of pleasure by stimulating certain centers of the brain. When they feel upset, people will simply activate their electrodes to achieve an immediate high.

Although far-fetched—and ultimately improbable—such a futuristic fantasy is based on fact. The brain does have pleasure centers in several areas, including some in the  limbic system . Consisting of a series of doughnut-shaped structures that include the amygdala and hippocampus, the limbic system borders the top of the central core and has connections with the cerebral cortex (see Figure 4).

FIGURE 4 The limbic system is involved in self-preservation, learning, memory, and the experience of pleasure.

©McGraw-Hill Global Education Holdings LLC, 1995.

The structures of the limbic system jointly control a variety of basic functions relating to emotions and self-preservation, such as eating, aggression, and reproduction. Injury to the limbic system can produce striking changes in behavior. For example, injury to the amygdala, which is involved in fear and aggression, can turn animals that are usually docile and tame into belligerent savages. Conversely, animals that are usually wild and uncontrollable may become meek and obedient following injury to the amygdala (Gontkovsky, 2005; Smith et al., 2013; Reznikova et al., 2015).

Research examining the effects of mild electric shocks to parts of the limbic system and other parts of the brain has produced some thought-provoking findings. In one classic experiment, rats that pressed a bar received mild electric stimulation through an electrode implanted in their brains, which produced pleasurable feelings. Even starving rats on their way to food would stop to press the bar as many times as they could. Some rats would actually stimulate themselves literally thousands of times an hour—until they collapsed with fatigue (Routtenberg & Lindy, 1965; Fountas & Smith, 2007).

Some humans have also experienced the extraordinarily pleasurable quality of certain kinds of stimulation: As part of the treatment for certain Page 68kinds of brain disorders, some people have received electrical stimulation to certain areas of the limbic system. Although at a loss to describe just what it feels like, these people report the experience to be intensely pleasurable, similar in some respects to sexual orgasm.

The limbic system and hippocampus, in particular, play an important role in learning and memory. Their importance is demonstrated in certain patients with epilepsy, who, in an effort to stop their seizures, have had portions of the limbic system removed. One unintended consequence of the surgery is that individuals sometimes have difficulty learning and remembering new information. In one case, a patient who had undergone surgery was unable to remember where he lived, although he had resided at the same address for 8 years. Further, even though the patient was able to carry on animated conversations, he was unable, a few minutes later, to recall what had been discussed (Milner, 1966; Grimm, 2011; de Voogd et al., 2017).

The limbic system, then, is involved in several important functions, including self-preservation, learning, memory, and the experience of pleasure. These functions are hardly unique to humans; in fact, the limbic system is sometimes referred to as the “animal brain” because its structures and functions are so similar to those of other mammals. To identify the part of the brain that provides the complex and subtle capabilities that are uniquely human, we need to turn to another structure—the cerebral cortex.

The Cerebral Cortex: Our “New Brain”

As we have proceeded up the spinal cord and into the brain, our discussion has centered on areas of the brain that control functions similar to those found in less sophisticated organisms. But where, you may be asking, are the portions of the brain that enable humans to do what they do best and that distinguish humans from all other animals? Those unique features of the human brain—indeed, the very capabilities that allow you to come up with such a question in the first place—are embodied in the ability to think, evaluate, and make complex judgments. The principal location of these abilities, along with many others, is the  cerebral cortex .

The cerebral cortex is referred to as the “new brain” because of its relatively recent evolution. It consists of a mass of deeply folded, rippled, convoluted tissue. Although only about 1/12 of an inch thick, it would, if flattened out, cover an area more than 2 feet square. This configuration allows the surface area of the cortex to be considerably greater than it would be if it were smoother and more uniformly packed into the skull. The uneven shape also permits a high level of integration of neurons, allowing sophisticated information processing.

The cerebral cortex consists of four major sections called  lobes . Each lobe has specialized areas that relate to particular functions. If we take a side view of the brain, the frontal lobes lie at the front center of the cortex and the parietal lobes lie behind them. The temporal lobes are found in the lower-center portion of the cortex, with the occipital lobes lying behind them. These four sets of lobes are physically separated by deep grooves called sulci. Figure 5 shows the four areas.

FIGURE 5 The cerebral cortex of the brain. The major physical structures of the cerebral cortex are called lobes. This figure also illustrates the functions associated with particular areas of the cerebral cortex. Are any areas of the cerebral cortex present in nonhuman animals?

©Ron Krisel/Getty Images

Another way to describe the brain is in terms of the functions associated with a particular area. Figure 5 also shows the specialized regions within the lobes related to specific functions and areas of the body. Three major areas are known: the motor areas, the sensory areas, and the association areas. Although we will discuss these areas as though they were separate and independent, keep in mind that this is an oversimplification. In most instances, behavior is influenced simultaneously by several structures and areas within the brain, operating interdependently. To give one example, people use different areas of the brain when they create sentences (a verbal task) compared with when they improvise musical tunes. Furthermore, when people suffer brain injury, uninjured portions of the brain can sometimes take over the functions that were previously handled by the damaged area. In short, the brain is extraordinarily adaptable (Sacks, 2003; Boller, 2004; Brown, Martinez, & Parsons, 2006).

THE MOTOR AREA OF THE CORTEX

If you look at the frontal lobe in Figure 5, you will see a shaded portion labeled  motor area . This part of the cortex is largely responsible for the body’s voluntary movement. Every portion of the motor area corresponds to a specific locale within the body. If we were to insert an electrode into a particular part of the motor area of the cortex and apply mild electrical stimulation, there would be involuntary movement in the corresponding part of the body. If we moved to another part of the motor area and stimulated it, a different part of the body would move.

The motor area is so well mapped that researchers have identified the amount and relative location of cortical tissue used to produce movement in specific parts of the human body. For example, the control of movements that are relatively large scale and require little precision, such as the movement of a knee or a hip, is centered in a very small space in the motor area. In contrast, movements that must be precise and delicate, such as facial expressions and finger movements, are controlled by a considerably larger portion of the motor area (Schwenkreis et al., 2007).

In short, the motor area of the cortex provides a guide to the degree of complexity and the importance of the motor capabilities of specific parts of the body. In fact, it may do even more: Increasing evidence shows that not only does the motor cortex control different parts of the body, but it may also direct body parts into complex postures, such as the stance of a football center just before the ball is snapped to the quarterback or a swimmer standing at the edge of a diving board (Pool et al., 2013; Massé-Alarie et al., 2017).

Ultimately, movement, like other behavior, is produced through the coordinated firing of a complex variety of neurons in the nervous system. The neurons that produce movement are linked in elaborate ways and work closely together.

THE SENSORY AREA OF THE CORTEX

Given the one-to-one correspondence between the motor area and body location, it is not surprising to find a similar relationship between specific portions of the cortex and Page 70specific senses. The  sensory area  of the cortex includes three regions: one that corresponds primarily to body sensations (including touch and pressure), one relating to sight, and a third relating to sound.

For instance, the somatosensory area in the parietal lobe encompasses specific locations associated with the ability to perceive touch and pressure in a particular area of the body. As with the motor area, the amount of brain tissue related to a particular location on the body determines the degree of sensitivity of that location. Specifically, the greater the area devoted to a specific area of the body within the cortex, the more sensitive is that area of the body.

For example, our fingers are related to a larger portion of the somatosensory area in the brain and are the most sensitive to touch. The weird-looking individual in Figure 6 shows what we would look like if the size of every external part of our body corresponded to the amount of brain tissue related to touch sensitivity.

The senses of sound and sight are also represented in specific areas of the cerebral cortex. An auditory area located in the temporal lobe is responsible for the sense of hearing. If the auditory area is stimulated electrically, a person will hear sounds such as clicks or hums. It also appears that particular locations within the auditory area respond to specific pitches (Tsuchida, Ueno, & Shimada, 2015; Anderson, Lazard, & Hartley, 2017).

The visual area in the cortex, located in the occipital lobe, responds in the same way to electrical stimulation. Stimulation by electrodes produces the experience of flashes of light or colors, suggesting that the raw sensory input of images from the eyes is received in this area of the brain and transformed into meaningful stimuli. The visual area provides another example of how areas of the brain are intimately related to specific areas of the body: Specific structures in the eye are related to a particular part of the cortex—with, as you might guess, more area of the brain given to the most sensitive portions of the retina (Stenbacka & Vanni, 2007; Libedinsky & Livingstone, 2011).

THE ASSOCIATION AREAS OF THE CORTEX

In a freak accident in 1848, an explosion drove a 3-foot-long iron bar completely through the skull of railroad worker Phineas Gage, where it remained after the accident. Amazingly, Gage survived and, despite the rod lodged through his head, a few minutes later seemed to be fine.

But he wasn’t. Before the accident, Gage was hardworking and cautious. Afterward, he became irresponsible, drank heavily, and drifted from one wild scheme to another. In the words of one of his physicians, “He was ‘no longer Gage’” (Harlow, 1869).

What had happened to the old Gage? Although there is no way of knowing for sure, we can speculate that the accident injured the region of Gage’s cerebral cortex known as the association areas. The  association areas  are the site of higher mental processes such as thinking, language, memory, and speech.

The association areas make up a large portion of the cerebral cortex. The association areas control executive functions, which are abilities that are related to planning, goal setting, judgment, and impulse control.

Much of our understanding of the association areas comes from patients who, like Phineas Gage, have suffered some type of brain injury. For example, when parts of the association areas are damaged, people undergo personality changes that affect their ability to make moral judgments and process emotions. At the same time, people with damage in those areas can still be capable of reasoning logically, performing calculations, and recalling information (Bechara et al., 1994).

FIGURE 6 The greater the amount of tissue in the somatosensory area of the brain that is related to a specific body part, the more sensitive is that body part. If the size of our body parts reflected the corresponding amount of brain tissue, we would look like this strange creature.

©Natural History Museum, London/Science Source

Injuries to the association areas of the brain can produce aphasia, problems with language. In Broca’s aphasia, Page 71speech becomes halting, laborious, and often ungrammatical, and a speaker is unable to find the right words. In contrast, Wernicke’s aphasia produces difficulties both in understanding others’ speech and in the production of language. The disorder is characterized by speech that sounds fluent but makes no sense, as in this example from a Wernicke’s patient: “Boy, I’m sweating, I’m awful nervous, you know, once in a while I get caught up, I can’t mention the tarripoi, a month ago, quite a little. . .” (Caplan, Waters, & Dede, 2007; Robson et al., 2013; Ardila, 2015).

Neuroplasticity and the Brain

Shortly after he was born, Jacob Stark’s arms and legs started jerking every 20 minutes. Weeks later he could not focus his eyes on his mother’s face. The diagnosis: uncontrollable epileptic seizures involving his entire brain.

His mother, Sally Stark, recalled: “When Jacob was 2½ months old, they said he would never learn to sit up, would never be able to feed himself. . . . They told us to take him home, love him, and find an institution.” (Blakeslee, 1992)

Instead, Jacob had brain surgery when he was 5 months old in which physicians removed 20% of his brain. The operation was a complete success. Three years later, Jacob seemed normal in every way, with no sign of seizures.

The surgery that helped Jacob was based on the premise that the diseased part of his brain was producing seizures throughout the brain. Surgeons reasoned that if they removed the misfiring portion, the remaining parts of the brain, which appeared intact in PET scans, would take over. They correctly bet that Jacob could still lead a normal life after surgery, particularly because the surgery was being done at so young an age.

The success of Jacob’s surgery illustrates that the brain has the ability to shift functions to different locations after injury to a specific area or in cases of surgery. But equally encouraging are some new findings about the regenerative powers of the brain and nervous system.

Scientists have learned in recent years that the brain continually changes, reorganizes itself, and is far more resilient than they once thought.  Neuroplasticity  refers to the brain’s ability to change throughout the life span through the addition of new neurons, new interconnections between neurons, and the reorganization of information-processing areas.

Advances in our understanding of neuroplasticity have changed the earlier view that no new brain cells are created after childhood. The reality is very different: Not only do the interconnections between neurons become more complex throughout life, but it now appears that new neurons are also created in certain areas of the brain during adulthood—a process called neurogenesis. Each day, thousands of new neurons are created, especially in areas of the brain related to learning and memory (Shors, 2009; Kempermann, 2011; Apple, Fonseca, & Kokovay, 2017).

The ability of neurons to renew themselves during adulthood has significant implications for the potential treatment of disorders of the nervous system (see Neuroscience in Your Life). For example, drugs that trigger the development of new neurons might be used to counter such diseases as Alzheimer’s, which are produced when neurons die (Waddell & Shors, 2008; Hamilton et al., 2013; Ekonomou et al., 2015).

Furthermore, specific experiences can modify the way in which information is processed. For example, if you learn to read Braille, the amount of tissue in your cortex related to sensation in the fingertips will expand. Similarly, if you take up the violin, the area of the brain that receives messages from your fingers will grow—but only relating to the fingers that actually move across the violin’s strings (Schwartz & Begley, 2002; Kolb, Gibb, & Robinson, 2003).

The future also holds promise for people who suffer from the tremors and loss of motor control produced by Parkinson’s disease, although the research is mired in controversy. Because Parkinson’s disease is caused by a gradual loss of cells that stimulate the production of dopamine in the brain, many investigators have reasoned that a procedure that would increase the supply of dopamine might be effective. They seem to be on the 

 Page 72right track. When stem cells—immature cells from human fetuses that have the potential to develop into a variety of specialized cell types, depending on where they are implanted—are injected directly into the brains of Parkinson’s sufferers, they take root and stimulate dopamine production. Preliminary results have been promising, with some patients showing great improvement (Parish & Arenas, 2007; Newman & Bakay, 2008; Wang et al., 2011).

NEUROSCIENCE IN YOUR LIFE: THE PLASTIC BRAIN

The brain is highly plastic, meaning that it can change in significant ways over the course of the life span. For example, brain plasticity is apparent in patients who lose a limb due to injury. Many such patients experience pain in their missing limb, called phantom limb pain. In a recent study, brain scans of participants with phantom hand pain showed changes in activity within sensory and motor brain regions. For example, regions involved in processing elbow information migrated into regions that previously processed missing hand information.

The images below show brain activity when participants moved their elbows (left) and hands (right; imagined for amputees). In the column labeled elbows, we see differences between activity during movement and rest (yellow indicates the greatest differences) in the same areas as in the column labeled hands, indicating that activity for elbow movements has migrated into regions for hand movements (Raffin et al., 2016).

Source: Adapted from Raffin, E., Richard, N., Giraux, P., & Reilly, K. T. (2016). Primary motor cortex changes after amputation correlate with phantom limb pain and the ability to move the phantom limb. Neuroimage, 130, 134–144.

Stem cells thus hold great promise. When a stem cell divides, each newly created cell has the potential to be transformed into more specialized cells that have the potential to repair damaged cells. Because many of the most disabling diseases, ranging from cancer to stroke, result from cell damage, the potential of stem cells to revolutionize medicine is significant.

However, because the source of implanted stem cells typically is aborted fetuses, their use is controversial. Some critics have argued that the use of stem cells in research and treatment should be prohibited, while supporters argue that the potential benefits of the research are so great that stem cell research should be unrestricted. The issue has been politicized, and the question of whether and how stem cell research should be regulated is not clear (Giacomini, Baylis, & Robert, 2007; Holden, 2007; Towns, 2017).

The Specialization of the Hemispheres: Two Brains or One?

The most recent development, at least in evolutionary terms, in the organization and operation of the human brain probably occurred in the last several million years: a specialization of the functions controlled by the left and right sides of the brain (Hopkins & Cantalupo, 2008; MacNeilage, Rogers, & Vallortigara, 2009; Tommasi, 2009).

The brain is divided into two roughly mirror-image halves. Just as we have two arms, two legs, and two lungs, we have a left brain and a right brain. Because of the Page 73way nerves in the brain are connected to the rest of the body, these symmetrical left and right halves, called  hemispheres , control motion in—and receive sensation from—the side of the body opposite their location. The left hemisphere of the brain, then, generally controls the right side of the body, and the right hemisphere controls the left side of the body. Thus, damage to the right side of the brain is typically indicated by functional difficulties in the left side of the body.

Despite the appearance of similarity between the two hemispheres of the brain, they are somewhat different in the functions they control and in the ways they control them. Certain behaviors are more likely to reflect activity in one hemisphere than in the other, or are  lateralized .

For example, for most people, language processing occurs more in the left side of the brain. In general, the left hemisphere concentrates more on tasks that require verbal competence, such as speaking, reading, thinking, and reasoning. In addition, the left hemisphere tends to process information sequentially, one bit at a time (Hines, 2004).

The right hemisphere has its own strengths, particularly in nonverbal areas such as the understanding of spatial relationships, recognition of patterns and drawings, music, and emotional expression. The right hemisphere tends to process information globally, considering it as a whole (Holowka & Petitto, 2002; Gotts et al., 2013; Longo et al., 2015).

Study Alert

Although the hemispheres of the brain specialize in particular kinds of functions, the degree of specialization is not great, and the two hemispheres work interdependently.

The degree and nature of lateralization vary from one person to another. If, like most people, you are right-handed, the control of language is probably concentrated more in your left hemisphere. By contrast, if you are among the 10% of people who are left-handed or are ambidextrous (you use both hands interchangeably), it is much more likely that the language centers of your brain are located more in the right hemisphere or are divided equally between the left and right hemispheres.

Keep in mind that despite the different strengths of the two hemispheres, the differences in specialization between the hemispheres are not great. Furthermore, the two hemispheres of the brain function in tandem. It is a mistake to think of particular kinds of information as being processed solely in the right or the left hemisphere. The hemispheres work interdependently in deciphering, interpreting, and reacting to the world.

In addition, people who suffer injury to the left side of the brain and lose linguistic capabilities often recover the ability to speak: The right side of the brain often takes over some of the functions of the left side, especially in young children; the extent of recovery increases the earlier the injury occurs (Johnston, 2004).

PsychTech

Using a procedure called hemispherectomy, in which an entire hemisphere of the brain is removed, surgeons ended Christina Santhouse’s seizures, which occurred at the rate of hundreds a day. Despite the removal of the right side of her brain, Christina recently completed a master’s degree in speech pathology.

Furthermore, not every researcher believes that the differences between the two hemispheres of the brain are terribly significant. According to neuroscientist Stephen Kosslyn, a more critical difference occurs in processing between the upper and lower halves of the brain. In his theory, the top-brain system of the brain specializes in planning and goal-setting. In contrast, the bottom-brain system helps classify information coming from our senses, allowing us to understand and classify information. It is still too early to know the accuracy of Kosslyn’s theory, but it provides an intriguing alternative to the notion that left-right brain differences are of primary importance (Kosslyn & Miller, 2013).

In any case, evidence continues to grow that the difference between processing in the left and right hemispheres are meaningful. For example, researchers have unearthed evidence that there may be subtle differences in brain lateralization patterns between males and females and members of different cultures, as we see in Exploring Diversity.

From the perspective of …

©Caia Images/Glow Images

An Office Worker Could personal differences in people’s specialization of right and left hemispheres be related to occupational success? For example, might a designer who relies on spatial skills have a different pattern of hemispheric specialization than does a lawyer?

Exploring Diversity

Human Diversity and the Brain

The interplay of biology and environment in behavior is especially clear when we consider evidence suggesting that even in brain structure and function, there are both sex and cultural differences. Let’s consider sex differences first. Accumulating evidence seems to show intriguing differences in males’ and females’ brain lateralization and weight (Boles, 2005; Clements, Rimrodt, & Abel, 2006; Joel & McCarthy, 2017).

For instance, the two sexes show differences in the speed at which their brains develop. Young girls show earlier development in the frontal lobes, which control aggressiveness and language development. On the other hand, boys’ brains develop faster in the visual region that facilitates visual and spatial tasks such as geometry (Giedd et al., 2010; Raznahan et al., 2010).

Furthermore, most males tend to show greater lateralization of language in the left hemisphere. For them, language is clearly relegated largely to the left side of the brain. In contrast, women display less lateralization, with language abilities apt to be more evenly divided between the two hemispheres. Such differences in brain lateralization may account, in part, for the superiority often displayed by females on certain measures of verbal skills, such as the onset and fluency of speech (Petersson et al., 2007; Mercadillo et al., 2011).

Other research suggests that men’s brains are somewhat bigger than women’s brains, even after taking differences in body size into account. In contrast, part of the corpus callosum, a bundle of fibers that connects the hemispheres of the brain, is proportionally larger in women than in men (Smith et al., 2007; Taki et al., 2013).

The meaning of such sex differences is far from clear. Consider one possibility related to differences in the proportional size of the corpus callosum: Its greater size in women may permit stronger connections to develop between the parts of the brain that control speech. In turn, this would explain why speech tends to emerge slightly earlier in girls than in boys.

Before we rush to such a conclusion, though, we must consider an alternative hypothesis: The reason verbal abilities emerge earlier in girls may be that infant girls receive greater encouragement to talk than do infant boys. In turn, this greater early experience may foster the growth of certain parts of the brain. Hence, physical brain differences may be a reflection of social and environmental influences rather than a cause of the differences in men’s and women’s behavior. At this point, it is impossible to know which of these alternative hypotheses is correct.

Furthermore, newer research suggests that most brains contain elements of male and female characteristics. Such findings contradict the notion that a brain is essentially either male or female (Denworth, 2017).

Culture also gives rise to differences in brain size and lateralization. For example, the volume of gray-matter material in the cortex is greater in higher-income adolescents than in low-income adolescents. Furthermore, brain development is related to differences in academic achievement between students of different income levels. Specifically, the brain’s cortex is thicker in higher-income students than in lower-income students, and cortex configuration is related to their academic achievement (Mackey et al., 2015).

Clearly, our brains reflect a combination of genetically determined structure and functioning. But they also reflect the impact of the social and cultural experiences to which we are exposed.

The Split Brain: Exploring the Two Hemispheres

When Vicki visited her neurologist, she was desperate: Her frequent and severe epileptic seizures weren’t just interfering with her day-to-day life—they were putting her in danger. She never knew when she might just collapse suddenly, making many mundane situations such as climbing stairs potentially life-threatening for her.

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Vicki’s neurologist had a solution, but a radical and potentially dangerous one: surgically severing the bundle of fibers connecting the two hemispheres of her brain. This procedure would stop the firestorms of electrical impulses that were causing Vicki’s seizures, but it would also have its own curious effects on her day-to-day functioning.

In the months after the surgery, Vicki was relieved to be free of the seizures that had taken over her life. But she had new challenges to overcome. Simple tasks such as food shopping or even dressing herself became lengthy ordeals—not because she had difficulty moving or thinking but because the two sides of her brain no longer worked in a coordinated way. Each side directed its half of the body to work independently of the other (Wolman, 2012).

People like Vicki, whose corpus collosums have been cut or injured, are called split-brain patients. They offer a rare opportunity for researchers investigating the independent functioning of the two hemispheres of the brain. For example, psychologist Roger Sperry—who won the Nobel Prize for his work—developed a number of ingenious techniques for studying how each hemisphere operates (Sperry, 1982; Savazzi et al., 2007; Bagattini et al., 2015).

In one experimental procedure, patients who were prevented from seeing an object by a screen touched the object with their right hand and were asked to name it (see Figure 7). Because the right side of the body corresponds to the language-oriented left side of the brain, split-brain patients were able to name it. However, if patients touched the object with their left hand, they were unable to name it aloud, even though the information had registered in their brains. When the screen was removed, patients could identify the object they had touched. Information can be learned and remembered, then, using only the right side of the brain. (By the way, unless you’ve had split-brain surgery, this experiment won’t work with you because the bundle of fibers connecting the two hemispheres of a normal brain immediately transfers the information from one hemisphere to the other.)

FIGURE 7 Hemispheres of the brain. (a) The corpus callosum connects the cerebral hemispheres of the brain, as shown in this cross section. (b) A split-brain patient is tested by touching objects behind a screen. Patients could name the objects they touched with their right hand but couldn’t name them when they touched them with their left hand. If a split-brain patient with her eyes closed was given a pencil to hold and called it a pencil, what hand was the pencil in?

(a and b): ©McGraw-Hill Global Education Holdings LLC, 2008.

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It is clear from experiments like this one that the right and left hemispheres of the brain specialize in handling different sorts of information. At the same time, it is important to realize that both hemispheres are capable of understanding, knowing, and being aware of the world, in somewhat different ways. The two hemispheres, then, should be regarded as different in terms of the efficiency with which they process certain kinds of information, rather than as two entirely separate brains. The hemispheres work interdependently to allow the full range and richness of thought of which humans are capable.

BECOMING AN INFORMED CONSUMER of Psychology

Learning to Control Your Heart—and Mind—Through Biofeedback

When Tammy DeMichael was involved in a horrific car accident that broke her neck and crushed her spinal cord, experts told her that she was doomed to be a quadriplegic for the rest of her life, unable to move from the neck down. But they were wrong. Not only did she regain the use of her arms, but she also was able to walk 60 feet with a cane (Hess, Houg, & Tammaro, 2007).

The key to DeMichael’s astounding recovery: biofeedback.  Biofeedback  is a procedure in which a person learns to control through conscious thought internal physiological processes such as blood pressure, heart and respiration rate, skin temperature, sweating, and the constriction of particular muscles. Although it traditionally had been thought that heart rate, respiration rate, blood pressure, and other bodily functions are under the control of parts of the brain over which we have no influence, psychologists have discovered that these responses are actually susceptible to voluntary control (Cho, Holyoak, & Cannon, 2007; Badke et al., 2011).

In biofeedback, a person is hooked up to electronic devices that provide continuous feedback relating to the physiological response in question. For instance, someone trying to control headaches through biofeedback might have electronic sensors placed on certain muscles on her head and learn to control the constriction and relaxation of those muscles. Later, when she felt a headache starting, she could relax the relevant muscles and abort the pain (Andrasik, 2007; Nestoriuc et al., 2008; Magis & Schoenen, 2011).

DeMichael’s treatment was related to a form of biofeedback called neurofeedback, in which brain activity is displayed for a patient. Because not all of her nervous system’s connections between the brain and her legs were severed, she was able to learn how to send messages to specific muscles, “ordering” them to move. Although it took more than a year, DeMichael was successful in restoring a large degree of her mobility.

Although the control of physiological processes through the use of biofeedback is not easy to learn, it has been employed with success in a variety of ailments, including emotional problems (such as anxiety, depression, phobias, tension headaches, insomnia, and hyperactivity), physical illnesses with a psychological component (such as asthma, high blood pressure, ulcers, muscle spasms, and migraine headaches), and physical problems (such as DeMichael’s injuries, strokes, cerebral palsy, and curvature of the spine) (Morone & Greco, 2007; Reiner, 2008; Dias & van Deusen, 2011).

RECAP/EVALUATE/RETHINK

RECAP

LO 7-1 How do researchers identify the major parts and functions of the brain?

•Brain scans take a “snapshot” of the internal workings of the brain without having to cut surgically into a person’s skull. Major brain-scanning techniques include the electroencephalogram (EEG), positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation imaging (TMS).

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