coon_dennis_mitterer_john_o_introduction_to_psychology_gatew-88-117.pdf

preview Finding Music in Walnut Grapefruit Tofu Your authors recently shared an evening together in Tucson, such a squishy little blob of tissue allow us to make music of Arizona, watching some fiery Spanish flamenco. We both had...

preview Finding Music in Walnut Grapefruit Tofu Your authors recently shared an evening together in Tucson, such a squishy little blob of tissue allow us to make music of Arizona, watching some fiery Spanish flamenco. We both had exquisite beauty? To seek a cure for cancer? To fall in love? Or to brains on our minds. (Really!) The guitarist and dancer were read a book like this one? passionate and brilliant. If they had been athletes, you would Each of the billions of nerve cells in your brain is linked to say they were “in the zone.” Of course, in everything from clas- thousands of others. The resulting network allows you to pro- sical to jazz to hip-hop, musicians regularly make music that cess immense amounts of information. In fact, there may be no machine could duplicate. A virtual Bruce Springsteen? A more possible pathways between the neurons in your brain mechanical Beyoncé? We doubt it. That’s why music is such a than there are stars in the visible universe! Undeniably, the good example of the central role the brain plays in all that is human brain is the most amazing of all computers. human. Scientists use the power of the brain to study the brain. Yet, Your 3-pound brain is wrinkled like a walnut, the size of a even now we must wonder if the brain will ever completely grapefruit, and the texture of tofu. The next time you are in a understand itself. Nevertheless, answers to many age-old ques- market that sells beef brains, stop and have a look. What you tions about the mind, consciousness, and knowledge lie buried will see is similar to your own brain, only smaller. How could within the brain. Let’s visit this fascinating realm. Neurons — Building a “Biocomputer” Like miniature cables, axons carry messages through the brain and nervous system. Altogether, your brain contains about 3 million Gateway Question: How do nerve cells operate and communicate? miles of axons (Rosenzweig, Breedlove, & Watson, 2004). While they may seem far removed from your daily life, 100 billion Axons “branch out” into smaller fibers ending in bulb-shaped tiny neurons (NOOR-ons: individual nerve cells) make up your axon terminals. By forming connections with the dendrites and brain. Neurons carry information from the senses to the brain, somas of other neurons, axon terminals allow information to pass where they process it. They also activate muscles and glands. Yet, a from neuron to neuron. single neuron is not very smart — it would take many just to make Now let’s summarize with a metaphor. Imagine that you are you blink. Millions of neurons must send messages at the same standing in a long line of people who are holding hands. A person time to produce even the most fleeting thought. When a musician on the far right end of the line wants to silently send a message to such as Eric Clapton plays a guitar riff, literally billions of neurons the person on the left end. She does this by pressing the hand of may be involved (Kalat, 2007). the person to her left, who presses the hand of the person to his Your brainpower arises because individual neurons link to left, and so on. The message arrives at your right hand (your den- one another in tight clumps and long “chains.” Each neuron drites). You decide whether to pass it on. (You are the soma.) The receives messages from many others and sends its own message on. message goes out through your left arm (the axon). With your left Everything you think, feel, or do can be traced back to electrical hand (the axon terminals), you squeeze the hand of the person to impulses flashing through spidery networks of neurons. When your left, and the message moves on. neurons form vast networks, they produce intelligence and con- sciousness. Let’s see how neurons operate and how the nervous The Nerve Impulse system is “wired.” Electrically charged molecules called ions (EYE-ons) are found inside Parts of a Neuron each neuron ( Figure 2.2). Other ions lie outside the cell. Some ions have a positive electrical charge, and some are negative. When a neu- What does a neuron look like? What are its main parts? No two neu- ron is inactive, more of these “plus” charges exist outside the neuron rons are exactly alike, but most have four basic parts ( Figure 2.1). and more “minus” charges exist inside. As a result, the inside of each The dendrites (DEN-drytes), which look like tree roots, receive neuron in your brain has an electrical charge of about minus 70 milli- messages from other neurons. The soma (SOH-mah: cell body) volts. (A millivolt is one thousandth of a volt.) This charge allows does the same. In addition, the soma sends messages of its own each neuron in your brain to act like a tiny biological battery. (nerve impulses) down a thin fiber called the axon (AK-sahn). The electrical charge of an inactive neuron is called its resting Some axons are only.1 millimeter long. (That’s about the width potential. But neurons seldom get much rest: Messages arriving of a pencil line.) Others stretch up to a meter through the nervous from other neurons raise and lower the resting potential. If the system. (From the base of your spine to your big toe, for instance.) electrical charge rises to about minus 50 millivolts, the neuron 48  Brain and Behavior 49 Synapse (see Figure 2.6 for an enlarged view) cell.Figure 2.1 A neuron, or nerve In the right foreground you can Other neuron see a nerve cell fiber in cross section. The upper left photo gives a more real- istic picture of the shape of neurons. Nerve impulses usually travel from the dendrites and soma to the branching ends of the axon. The nerve cell shown Axon terminals here is a motor neuron. The axons of motor neurons stretch from the brain and spinal cord to muscles or glands of the body. Myelin Nerve impulse Neurilemma Soma (cell body) Nerve impulse Axon collateral (branch) Axon Nerve cell fiber Myelin sheath Axon Dendrites will reach its threshold, or trigger point for firing. (See Figure After each nerve impulse, the cell briefly dips below its resting 2.2.) It’s as if the neuron says, “Ah ha! It’s time to send a message to level and it becomes less willing to fire. This negative after-poten- my neighbors.” When a neuron reaches about 50 millivolts, an tial occurs because potassium ions (K) flow out of the neuron action potential, or nerve impulse, sweeps down the axon at up to while the membrane gates are open. (See Figure 2.4.) After a 200 miles per hour ( Figure 2.3). That may seem fast, but it still nerve impulse, ions flow both into and out of the axon, recharging takes at least a split second to react. That’s one reason why hitting a it for more action. In our model, it takes an instant for the row of 95-mile-per-hour major league fastball is so difficult. dominoes to be set up again. Soon, however, the axon is ready for What happens during an action potential? The axon membrane another wave of activity. is pierced by tiny tunnels or “holes,” called ion channels. Nor- mally, these tiny openings are blocked by molecules that act like “gates” or “doors.” During an action potential, the gates pop open. Neuron An individual nerve cell. This allows sodium ions (Na) to rush into the axon (Carlson, Dendrites Neuron fibers that receive incoming messages. 2007). The channels first open near the soma. Then gate after Soma The main body of a neuron or other cell. gate opens down the length of the axon as the action potential zips Axon Fiber that carries information away from the cell body of a along ( Figure 2.4). neuron. Each action potential is an all-or-nothing event (a nerve impulse Axon terminals Bulb-shaped structures at the ends of axons that form occurs completely or not at all). You might find it helpful to pic- synapses with the dendrites and somas other neurons. ture the axon as a row of dominoes set on end. Tipping over the Resting potential The electrical charge of a neuron at rest. dominoes is an all-or-nothing act. Once the first domino drops, Threshold The point at which a nerve impulse is triggered. a wave of falling blocks will zip rapidly to the end of the line. Similarly, when a nerve impulse is triggered near the soma, a wave Action potential The nerve impulse. of activity (the action potential) travels down the length of the Ion channels Tiny openings through the axon membrane. axon. This is what happens in long chains of neurons as a flamenco Negative after-potential A drop in electrical charge below the resting dancer’s brain tells her feet what to do next, beat after beat. potential. 50 CHAPTER 2 +30 Action potential Membrane potential 0 (in millivolts) Resting Negative potential after-potential Threshold –50 –70 Time + + + + + + + Figure 2.2 Electrical probes placed inside and outside an axon measure its activity. (The scale is exaggerated here. Such measurements require ultra-small electrodes, as described in this chapter.) The inside of an axon at rest – – – – – – – – – – – – – – + + + + + + + is about –60 to –70 millivolts, compared with the outside. Electrochemical changes in a neuron generate an action Axon potential. When sodium ions (Na) that have a positive charge rush into the cell, its interior briefly becomes positive. This is the action potential. After the action potential, positive potassium ions (K) flow out of the axon and restore its negative charge. (See Figure 2.3 for further explanation.) Figure 2.3 The inside of an axon nor- mally has a negative electrical charge. The Axon fluid surrounding an axon is normally positive. 1. In its resting state, the axon has a As an action potential passes along the axon, negatively charged interior. these charges reverse so that the interior of – – – – – – – – – – – – – the axon briefly becomes positive. This pro- + + + + + + + + + + + + cess is described in more detail in Figure 2.4. 2. During an action potential, positively Action potential charged atoms (ions) rush into the axon. This briefly changes the electrical charge inside the axon from negative to positive. Simultaneously, the charge outside the + + + + – – – – – – – – – axon becomes negative. – – – – + + + + + + + + 3. The action potential advances as Action potential positive and negative charges reverse in a moving zone of electrical activity that sweeps down the axon. – – – – + + + + – – – – – + + + + – – – – + + + + Action potential 4. After an action potential passes, positive ions rapidly flow out of the axon to quickly restore its negative charge. An outward flow of additional positive ions – – – – – – – – + + + + – returns the axon to its resting state. + + + + + + + – – – – + Saltatory Conduction The axons of some neurons (such as the one pictured in Fig- impossible to brake in time to avoid many automobile accidents ure 2.1) are coated with a fatty layer called myelin (MY-eh-lin). (or hit that major league fastball). When the myelin layer is dam- Small gaps in the myelin help nerve impulses move faster. Instead aged, a person may suffer from numbness, weakness, or paralysis. of passing down the entire length of the axon, the action poten- That, in fact, is what happens in multiple sclerosis, a disease that tial leaps from gap to gap, a process called saltatory conduction. occurs when the immune system attacks and destroys the myelin Without the added speed this allows, it would probably be in a person’s body.  Brain and Behavior 51 Action potential Presynaptic Resting potential axon terminal Axon Na+ Na+ – – – – – + + + + + Ion Synaptic gap channels + + + + + Synaptic – – – – – + + + + + vesicle Neurotransmitter Na+ Na+ Na+ Action potential Receptor site + + + + + – – – – – Postsynaptic dendrite K+ K+– K+ K+ + + + + + in tiny Figure 2.5 A highly magnified view of a synapse. Neurotransmitters are stored sacs called synaptic vesicles (VES-ih-kels). When a nerve impulse reaches + + + + + – – – – – the end of an axon, the vesicles move to the surface and release neurotransmitters. Axon repolarizes These molecules cross the synaptic gap to affect the next neuron. The size of the gap Thus,Figure 2.4 The interior of an axon. The right end of the top axon is at rest. it has a negative charge inside. An action potential begins when ion channels is exaggerated here; it is actually only about one millionth of an inch. Some transmit- ter molecules excite the next neuron and some inhibit its activity. open and sodium ions (Na) rush into the axon. In this drawing, the action potential would travel from left to right along the axon. In the lower axon, the action poten- tial has moved to the right. After it passes, potassium ions (K) flow out of the axon. rotransmitters. The sites are found in large numbers on nerve cell This quickly renews the negative charge inside the axon so that it can fire again. bodies and dendrites. Muscles and glands have receptor sites, too. Sodium ions that enter the axon during an action potential are pumped out more slowly. Removing them restores the original resting potential. Do neurotransmitters always trigger an action potential in the next neuron? No, but they do change the likelihood of an action potential in the next neuron. Some transmitters excite the next neuron (move it closer to firing). Others inhibit it (make firing Synapses and Neurotransmitters less likely). How does information move from one neuron to another? The nerve More than 100 transmitter chemicals are found in the brain. impulse is primarily electrical. That’s why electrically stimulating Some examples are acetylcholine, epinephrine, norepinephrine, the brain affects behavior. To prove the point, researcher José serotonin, dopamine, histamine, and various amino acids. Distur- Delgado once entered a bullring with a cape and a radio transmit- bances of any of these substances can have serious consequences. ter. The bull charged. Delgado retreated. At the last instant the For example, too little dopamine can cause the shaking and muscle speeding bull stopped short. Why? Because Delgado had placed tremors of Parkinson’s disease. Too much dopamine may cause the radio-activated electrodes (metal wires) deep within the bull’s severe mental disorder known as schizophrenia (Di Forti, Lappin, brain. These, in turn, stimulated “control centers” that brought & Murray, 2007). the bull to a halt (Horgan, 2005). Many drugs imitate, duplicate, or block neurotransmitters. In contrast to the nerve impulse, communication between For example, acetylcholine (ah-SEET-ul-KOH-leen) normally neurons is chemical. The microscopic space between two neu- activates muscles. Without acetylcholine, our flamenco musicians rons, over which messages pass, is called a synapse (SIN-aps) couldn’t even move, much less perform. That’s exactly how the ( Figure 2.5). When an action potential reaches the tips of the axon terminals, neurotransmitters (NOOR-oh-TRANS-mit- ers) are released into the synaptic gap. Neurotransmitters are Myelin A fatty layer coating some axons. chemicals that alter activity in neurons. Saltatory conduction The process by which nerve impulses conducted Let’s return to our metaphor of people standing in a line. To down the axons of neurons coated with myelin jump from gap to gap in be more accurate, you and the others shouldn’t be holding hands. the myelin layer. Instead, each person should have a squirt gun in his or her left Synapse The microscopic space between two neurons, over which hand. To pass along a message, you would squirt the right hand of messages pass. the person to your left. When that person notices this “message,” Neurotransmitter Any chemical released by a neuron that alters he or she would squirt the right hand of the person to the left, activity in other neurons. and so on. Receptor sites Areas on the surface of neurons and other cells that are When chemical molecules cross over a synapse, they attach sensitive to neurotransmitters or hormones. to special receiving areas on the next neuron. (See Figure 2.5.) Acetylcholine The neurotransmitter released by neurons to activate These tiny receptor sites on the cell membrane are sensitive to neu- muscles. 52 CHAPTER 2 drug curare (cue-RAH-ree) causes paralysis. By attaching to recep- tor sites on muscles, curare competes with acetylcholine. This + prevents acetylcholine from activating muscle cells. As a result, a person or animal given curare cannot move — a fact known to A South American Indians of the Amazon River Basin, who use curare as an arrow poison for hunting. + + – + Neural Regulators More subtle brain activities are affected by chemicals called neuro- – peptides (NOOR-oh-PEP-tides). Neuropeptides do not carry messages directly. Instead, they regulate the activity of other neu- rons. By doing so, they affect memory, pain, emotion, pleasure, moods, hunger, sexual behavior, and other basic processes. For example, when you touch something hot, you jerk your hand away. The messages for this action are carried by neurotransmitters. At weaker Figure 2.6 A small neural network. Neuron A receives inputs from two the same time, pain may cause the brain to release enkephalins (en- and one stronger excitatory connections () and two inhibitory connec- KEF-ah-lins). These opiate-like neural regulators relieve pain and tions () and combines the inputs into a “decision” to launch an action potential, which may help trigger further synaptic transmissions in other neurons. stress. Related chemicals called endorphins (en-DORF-ins) are released by the pituitary gland. Together, these chemicals reduce the pain so that it is not too disabling (Drolet et al., 2001). arrive close in time, the neuron will fire — but only if it doesn’t Such discoveries help explain the painkilling effect of placebos get too many “inhibiting” messages that push it away from its (fake pills or injections), which raise endorphin levels (Stewart- trigger point. In this way, messages are combined before a neuron Williams, 2004). A release of endorphins also seems to underlie “decides” to fire its all-or-nothing action potential. “runner’s high,” masochism, acupuncture, and the euphoria some- Let’s try another metaphor. You are out shopping for new times associated with childbirth, painful initiation rites, and even jeans with five friends. Three of them think you should buy the sport parachuting ( Janssen & Arntz, 2001). In each case, pain and jeans (your best friend is especially positive) and two think you stress cause the release of endorphins. These in turn induce feel- shouldn’t. Because, on balance, their input is positive, you go ahead ings of pleasure or euphoria similar to being “high” on morphine. and buy the jeans. Maybe you even tell some other friends they People who say they are “addicted” to running may be closer to the should buy those jeans as well. Similarly, any single neuron in a truth than they realize. neural network “listens” to the neurons that synapse with it and combines that input into an output. At any instant, a single neuron may weigh hundreds or thousands of inputs to produce an outgo- bridges ing message. After the neuron recovers from the resulting action To learn more about how pain can sometimes produce potential, it again combines the inputs, which may have changed in feelings of relaxation or euphoria, see Chapter 4, the meantime, into another output, and another, and another. pages 143–144. In this way, each neuron in your brain functions as a tiny com- puter. Compared with the average laptop computer, a neuron is terribly simple and slow. But multiply these events by 100 billion neurons and 100 trillion synapses, all operating at the same time, Ultimately, neural regulators may help explain depression, and you have an amazing computer — one that could easily fit schizophrenia, drug addiction, and other puzzling topics. For inside a shoebox. example, women who suffer from severe premenstrual pain and distress have unusually low endorphin levels (Straneva et al., Neuroplasticity 2002). The neural networks in your brain constantly change. The term neuroplasticity refers to the capacity of our brains to change in Neural Networks response to experience. New synapses may form between neurons Let’s put together what we now know about the nerve impulse and or synaptic connections may grow stronger. ( Figure 2.6 shows synaptic transmission to see how neural networks process informa- one particularly strong synapse — the large .) Other synaptic tion in our brains. Figure 2.6 shows a small part of a neural connections may weaken and might even die. Every new experi- network. Five neurons synapse with a single neuron that, in turn, ence you have is reflected in changes in your brain. For example, connects with three more neurons. At the point in time depicted rats raised in a complex environment have more synapses and lon- in the diagram, the single neuron is receiving one stronger and two ger dendrites in their brains than rats raised in a simpler environ- weaker excitatory messages () as well as two inhibitory ones (). ment (Kolb, Gibb, & Gorny, 2003). (See “You Can Change Your Does it fire an impulse? It depends: If enough “exciting” messages Mind, but Can You Change Your Brain?”)  Brain and Behavior 53 CRIT ICA L T H I N KI N G You Can Change Your Mind, but Can You Change Your Brain? You can always change your mind. But does ready to appear on Fear Factor). Images of stand language, but brain images revealed that have anything to do with your brain? their brains revealed reduced activity in the that the right sides of their brains had Philosophers have debated the relationship of brain areas involved in the phobia (Paquette become more active to compensate for their the mind to the brain (and the rest of the body) et al., 2003). Not only did they change their left-brain damage (Musso et al., 1999). Again, for centuries. Biopsychologists argue that every minds about spiders, they literally changed a learning experience changed their brains. mental event involves a brain event. their brains. Every time you learn something, you are In one study, people suffering from spi- Another study focused on patients with reshaping your living brain. There is even a der phobias were treated with cognitive language difficulties caused by damage fancy phrase to describe what you are doing: behavior therapy. (For more information, see to the left sides of their brains. To aid their self-directed neuroplasticity. Just think. As Chapter 15, pages 505–507.) recovery, the patients were given training in you study this psychology textbook you are After therapy, they could actually touch language comprehension. Not only did the changing your mind, and your brain, about spiders (although they might not have been training help improve their ability to under- psychology. The Nervous System — Central nervous Peripheral nervous Wired for Action system system Gateway Question: What are the major parts of the nervous system? Spinal Somatic Autonomic Brain cord Harry and Maya are playing catch with a football. This system system may look fairly simple. However, to merely toss the foot- (a) ball or catch it, a huge amount of information must be sensed, inter- Sympathetic Parasympathetic preted, and directed to countless muscle fibers. As they play, Harry system system and Maya’s neural circuits are ablaze with activity. Let’s explore the (b) “wiring diagram” that makes their game of catch possible. As you can see in Figure 2.7, the central nervous system Figure 2.7 Subparts of the nervous (CNS) consists of the brain and spinal cord. The brain carries out system. (a) Central nervous system. most of the “computing” in the nervous system. Harry must use (b) Peripheral nervous system. his brain to anticipate when and where the football will arrive. Harry’s brain communicates with the rest of his body through general, it controls voluntary behavior, such as when Maya tosses a large “cable” called the spinal cord. From there, messages flow the football or Tiger Woods hits a golf ball. In contrast, the auto- through the peripheral nervous system (PNS). This intricate nomic nervous system (ANS) serves the internal organs and network of nerves carries information to and from the CNS. glands. The word autonomic means “self-governing.” Activities Are nerves the same as neurons? No. Neurons are tiny cells. You would need a microscope to see one. Nerves are large bundles of neuron axons. You can easily see nerves without magnification. Neuropeptides Brain chemicals that regulate the activity of neurons, Nerves in the peripheral nervous system can regrow if they are such as enkephalins and endorphins. damaged. The axons of most neurons in nerves outside the brain Neuroplasticity The capacity of our brains to change in response to and spinal cord are covered by a thin layer of cells called the neuri- experience. lemma (NOOR-rih-LEM-ah). (Return to Figure 2.1.) The neu- Central nervous system (CNS) The brain and spinal cord. rilemma forms a “tunnel” that damaged fibers can follow as they Peripheral nervous system (PNS) All parts of the nervous system repair themselves. Because of this, patients can expect to regain outside the brain and spinal cord. some control over severed limbs once they have been reattached. Nerve A bundle of neuron fibers. Neurilemma A layer of cells that encases many axons. The Peripheral Nervous System Somatic nervous system (SNS) The system of nerves linking the spinal The peripheral system can be divided into two major parts (See cord with the body and sense organs. Figure 2.7). The somatic nervous system (SNS) carries mes- Autonomic nervous system (ANS) The system of nerves carrying sages to and from the sense organs and skeletal muscles. In information to and from the internal organs and glands. 54 CHAPTER 2 governed by the autonomic nervous system are mostly “vegeta- for “fight or flight” during times of danger or high emotion. In tive” or automatic, such as heart rate, digestion, and perspiration. essence, it arouses the body for action. Thus, messages carried by the somatic system can make your hand The parasympathetic branch quiets the body and returns it to move, but they cannot cause your eyes to dilate. Likewise, mes- a lower level of arousal. It is most active soon after an emotional sages carried by the ANS can stimulate digestion, but they cannot event. The parasympathetic branch also helps keep vital processes help you carry out a voluntary action, such as writing a letter. If such as heart rate, breathing, and digestion at moderate levels. Harry feels a flash of anger when he misses a catch, a brief burst Of course, both branches of the ANS are always active. At any of activity will spread through his autonomic system. given moment, their combined activity determines if your body is more or less relaxed or aroused. bridges The Spinal Cord The ANS plays a central role in our emotional lives. In fact, As mentioned earlier, the spinal cord connects the brain to other without the ANS a person would feel little emotion. See parts of the body. If you were to cut through this “cable,” you Chapter 10, pages 343–345 for more information about the would see columns of white matter (bundles of axons covered with ANS and emotion. myelin). This tissue is made up of axons that eventually leave the spinal cord to form the peripheral nervous system nerves. Thirty- one spinal nerves carry sensory and motor messages to and from The ANS and SNS work together to coordinate the body’s the spinal cord. In addition, 12 pairs of cranial nerves leave the internal reactions to events in the world outside. For example, if brain directly. Together, these nerves keep your entire body in a snarling dog lunges at you, the somatic system will control your communication with your brain. leg muscles so that you can run. At the same time, the autonomic Is the spinal cord’s only function to connect the brain to the periph- system will raise your blood pressure, quicken your heart, and so eral nervous system? Actually, the spinal cord can do some simple forth. The ANS can be divided into the sympathetic and parasym- “computing” of its own. Reflex arcs, which occur when a stimulus pathetic branches. Both are related to emotional responses, such provokes an automatic response, arise within the spinal cord, as crying, sweating, heart rate, and other involuntary behavior without any help from the brain ( Figure 2.9). Imagine that Maya ( Figure 2.8). steps on a thorn. (Yes, they’re still playing catch.) Pain is detected How do the branches of the autonomic system differ? The sym- in her foot by a sensory neuron (a nerve cell that carries messages pathetic branch is an “emergency” system. It prepares the body from the senses toward the CNS). Instantly, the sensory neuron fires off a message to Maya’s spinal cord. Parasympathetic Sympathetic Cell body of sensory neuron Constricts pupil Sensory Stimulates tears nerve Sensory neuron Stimulates salivation Dilates pupil Connector Inhibits heart rate Inhibits tears neuron Inhibits salivation Constricts respiration Spinal cord Activates sweat glands Constricts blood vessels (cross section) Motor neuron Increases heart rate Stimulates digestion Increases respiration Muscle cell responds Inhibits digestion by contracting Release of adrenaline Release of sugar from liver Relaxes bladder Inhibits elimination Inhibits genitals Contracts bladder Ejaculation in males Stimulates elimination Stimulates genitals arc,Figure 2.9 A sensory-motor or reflex, is set in motion by a stimulus to the skin (or other part of Sensory nervous Figure 2.8 Sympathetic and parasympathetic branches of the autonomic system. Both branches control involuntary actions. The sympathetic system the body). The nerve impulse travels to the spinal cord and then back out receptor in skin generally activates the body. The parasympathetic system generally quiets it. The to a muscle, which contracts. Such sympathetic branch relays its messages through clusters of nerve cells outside the reflexes provide an “automatic” pro- Stimulus to skin spinal cord. tective device for the body.  Brain and Behavior 55 Inside the spinal cord, the sensory neuron synapses with a con- While peripheral nerves can regrow, a serious injury to the nector neuron (a nerve cell that links two others). The connector brain or spinal cord is usually permanent. However, scientists neuron activates a motor neuron (a cell that carries commands from are starting to make progress repairing damaged neurons in the the CNS to muscles and glands). The muscle fibers are made up CNS. For instance, they have partially repaired cut spinal cords of effector cells (cells capable of producing a response). The muscle in rats. First they close the gap with nerve fibers from outside the cells contract and cause Maya’s foot to withdraw. Note that no spinal cord. Then they biochemically coax the severed spinal nerve brain activity is required for a reflex arc to occur. Maya’s body will fibers to grow through the “tunnels” (neurilemma) provided by react automatically to protect itself. the implanted fibers. Within months, rats treated this way regain In reality, even a simple reflex usually triggers more complex some use of their hind legs (Cheng, Cao, & Olson, 1996). activity. For example, muscles of Maya’s other leg must contract Similarly, medical researchers have already begun the first to support her as she shifts her weight. Even this can be done by human trials in which nerve grafts will be used to repair damaged the spinal cord, but it involves many more cells and several spinal spinal cords (Féron et al., 2005). Imagine what that could mean to nerves. Also, the spinal cord normally informs the brain of its a person confined to a wheelchair. Although it is unwise to raise actions. As her foot pulls away from the thorn, Maya will feel the false hopes, solutions to such problems are beginning to emerge. pain and think, “Ouch, what was that?” Nevertheless, it is wise to take good care of your own CNS. That Perhaps you have realized how adaptive it is to have a spinal cord means using seat belts when you drive, wearing a helmet if you ride capable of responding on its own. Such automatic responses leave a motorcycle or bicycle, wearing protective gear for sports, and the brains of our football stars free to deal with more important avoiding activities that pose a risk to your head or spinal cord. information — such as the location of trees, lampposts, and attrac- Can brain damage also be repaired? While we will be exploring tive onlookers — as they take turns making grandstand catches. the brain itself in more detail later on in the chapter, we can, for now, answer with an optimistic but cautious yes. (See “Repairing Your Brain.”) Before we go on to explore some of the research tools biopsy- chologists use, take some time to check out how much you’ve learned. KNOWL E DG E B U I L DE R Neurons and the Nervous System RECITE 1. The _______________ and ____________ are the receiving areas of a neuron where information from other neurons is accepted. 2. Nerve impulses are carried down the __________________ to the ______________ _______________________. 3. The ______________ potential becomes a(n) ______________ potential when a neuron passes the threshold for firing. 4. Neuropeptides are transmitter substances that help regulate the activity of neurons. T or F? 5. The somatic and autonomic systems are part of the ______________ nervous system. 6. Sodium and potassium ions flow across the synapse to trigger a nerve impulse in the receiving neuron. T or F? 7. The simplest behavior sequence is a _____________ ____________. 8. The parasympathetic nervous system is most active during times of high emotion. T or F? Continued Blend Images/Jupiter images Sympathetic branch A branch of the ANS that arouses the body. Parasympathetic branch A branch of the ANS that quiets the body. Reflex arc The simplest behavior, in which a stimulus provokes an automatic response. Each year spinal cord injuries rob many thousands of people of the ability to move. Yet there is growing hope that nerve-grafting techniques may someday Sensory neuron A nerve cell that carries information from the senses make it possible for some of these people to walk again. toward the CNS. 56 CHAPTER 2 C R IT ICAL T H I N KI N G Repairing Your Brain Until only a few years ago, it was widely loses cells daily, it simultaneously grows new the damaged area of Bobby’s brain (Zhang, believed that we are born with all the brain neurons to replace them. This process is called Zhang, & Chopp, 2005). Such techniques are cells we will ever have. This led to the depress- neurogenesis (noor-oh-JEN-uh-sis; the pro- beginning to offer new hope for people suf- ing idea that we all slowly go downhill, as the duction of new brain cells) (Kempermann, fering from a variety of other disabilities, such brain loses thousands of neurons every day. It 2005). Each day, thousands of new cells as blindness and Parkinson’s disease (Brinton also led to limited options, such as nerve cell originate deep within the brain, move to & Wang, 2006; Burke et al., 2007). transplants, for the treatment of brain damage the surface, and link up with other neurons But don’t these treatments assume that (Wong, Hodges, & Horsburgh, 2005). Imagine to become part of the brain’s circuitry. This is Bobby’s brain is still capable of neurogenesis? that Bobby M. suffered partial paralysis in his stunning news to brain scientists, who must What if it isn’t? Brilliant! Although a stroke left arm due to a stroke. (A stroke occurs when now figure out what the new cells do. Most most likely doesn’t damage the brain’s ability an artery in the brain becomes blocked or likely they are involved in learning, memory, to repair itself, it is quite possible that other bursts open. This interrupts blood flow and and our ability to adapt to changing circum- brain disorders do arise from impaired neuro- causes some brain tissue to die.) What could stances (Gould & Gross, 2002). genesis (Thompson et al., 2008). In fact, that is be done to help Bobby recover? One remedy The discovery of neurogenesis in adult exactly the theory proposed by neuroscientists involves injecting immature nerve cells into brains has raised hope that new treat- Carla Toro and Bill Deakin to explain the serious his damaged brain areas. This would allow ments can be found for some types of brain mental disorder schizophrenia (Toro & Deakin, the new cells to link up with existing neu- damage. For example, an approach called 2007). The brains of schizophrenic persons are rons in order to repair Bobby’s stroke dam- constraint-induced movement therapy could usually smaller than normal, indicating that age (Borlongan, Sanberg, & Freeman, 1999; be used to speed Bobby M.’s recovery. In they have fewer neurons. Toro and Deakin’s Zhang, Zhang, & Chopp, 2005). this case, Bobby’s good right arm would be idea is that the schizophrenic brain may be Rather than facing a steady decline, we restrained, forcing his impaired left arm to unable to continually create new neurons to now know that a healthy 75-year-old brain be more active, which would increase neu- replace old ones that have died. If they are has just as many neurons as it did when it rogenesis in the damaged part of his brain right, new therapies to promote neurogenesis was careening through life in the body of a (Taub, 2004). In another approach, drugs that may hold the key to treating schizophrenia, 25-year-old. Although it is true that the brain speed up neurogenesis could be injected into one of the most devastating mental illnesses. brain to the control of particular cognitive or behavioral func- REFLECT tions, such as being able to recognize faces or move your hands. Critical Thinking That is, they try to learn where functions are localized (located) in 9. What effect would you expect a drug to have if it blocked passage of the brain. Many techniques have been developed to help identify neurotransmitters across the synapse? brain structures and the functions they control. Relate To cope with all the technical terms in this section, think of neurons as strange little creatures. How do they act? What excites them? How do they Mapping Brain Structure communicate? To remember the functions of major branches of the ner- vous system, think about what you couldn’t do if each part were missing. Anatomists have learned much about brain structure by dissecting stimulant. (cutting apart) autopsied human and animal brains and examin- brain activity. If it blocked inhibitory messages, it would act as a powerful ing them under a microscope. Dissection reveals that the brain ranging effects. If the drug blocked excitatory synapses, it would depress is made up of many anatomically distinct areas or “parts.” Less 4. T 5. peripheral 6. F 7. reflex arc 8. F 9. Such a drug could have wide- Answers: 1. dendrites, soma 2. axon, axon terminals 3. resting, action intrusive newer methods, such as the CT scan and the MRI scan, can be used to map brain structures in living brains. CT Scan Computerized scanning equipment has revolutionized the study of brain structures and made it easier to identify brain diseases Research Methods — Charting and injuries. At best, conventional X-rays produce only shadowy the Brain’s Inner Realms images of the brain. Computed tomographic (CT) scanning is a specialized type of X-ray that does a much better job of making Gateway Question: How is the brain studied? the brain visible. In a CT scan, X-rays taken from a number of Biopsychology is the study of how biological processes, and espe- different angles are collected by a computer and formed into an cially those of the nervous system, relate to behavior. In their image of the brain. A CT scan can reveal the location of strokes, research, many biopsychologists try to relate specific parts of the injuries, tumors, and other brain disorders.  Brain and Behavior 57 recovery that has been miraculous by any measure, she even went on to appear before the U. S. Congress. Instead of relying on clinical studies, researchers have learned much from electrical stimulation of the brain (ESB) ( Fig- ure 2.11). For example, the surface of the brain can be “turned on” by stimulating it with a mild electrical current delivered through a thin insulated wire called an electrode. When this is done during brain surgery, the patient can describe what effect the stimulation had. (The brain has no pain receptors, so surgery can be done while a patient is awake. Only local painkillers are used for the scalp and CNRI/Photo Researchers, Inc. skull.) (Any volunteers?) Even structures below the surface of the brain can be activated by lowering a stimulating electrode, insulated except at the tip, into a target area inside the brain. ESB can call forth behavior with astonishing power. Instantly, it can bring about aggression, alertness, escape, eating, drinking, sleeping, movement, identify Figure 2.10 A colored MRI scan of the brain reveals many details. Can you any brain regions? euphoria, memories, speech, tears, and more. Could ESB be used to control a person against his or her will? It might seem that ESB could be used to control a person like a robot. But the details of emotions and behaviors elicited by ESB MRI Scan are modified by personality and circumstances. Sci-fi movies to Magnetic resonance imaging (MRI) uses a very strong magnetic the contrary, it would be impossible for a ruthless dictator to field, rather than X-rays, to produce an image of the body’s inte- enslave people by “radio controlling” their brains. rior. During an MRI scan, the body is placed inside a magnetic An alternate approach is ablation (ab-LAY-shun: surgical field. Processing by a computer then creates a three-dimensional model of the brain or body. Any two-dimensional plane, or slice, removal) of parts of the brain. (See Figure 2.11.) When ablation of the body can be selected and displayed as an image on a com- Deep-lesioning puter screen. MRI scans produce more detailed images than are Stimulation electrode electrode possible with CT scans, allowing us to peer into the living brain almost as if it were transparent ( Figure 2.10). Surgical ablation Exploring Brain Function How does the brain allow us to think, feel, perceive, or act? To answer questions like these, we must localize function by linking these psychological or behavioral capacities with particular brain struc- tures. In many instances, this has been done through clinical case brainFigure 2.11 The functions of structures are explored by selectively studies. Such studies examine changes in personality, behavior, or activating or removing them. Brain research sensory capacity caused by brain diseases or injuries. If damage to is often based on electrical stimulation, but a particular part of the brain consistently leads to a particular loss chemical stimulation is also used at times. of function, then we say the function is localized in that structure. Presumably, that part of the brain controls the same function in all of us. Neurogenesis The production of new brain cells. Consider, for example, the story of Kate Adamson (Adamson, Computed tomographic (CT) scanning A computer-enhanced X-ray 2004). At the age of 33, she had a stroke that caused catastrophic image of the brain or body. damage to her brainstem. This event left her with locked-in syn- Magnetic resonance imaging (MRI) A three-dimensional image of drome: One moment she was fine, and the next she was totally the brain or body, based on its response to a magnetic field. paralyzed, trapped in her own body and barely able to breathe. As Localization of function The research strategy of linking specific you can see, this clinical case suggests that our brainstems play a structures in the brain with specific psychological or behavioral role in the control of vital life functions, such as movement and functions. breathing. Clinical case study A detailed investigation of a single person, But what happened to Kate? Oh, yes. Unable to move a muscle, especially one suffering from some injury or disease. but still fully awake and aware, Kate thought she was going to die. Electrical stimulation of the brain (ESB) Direct electrical stimulation Her doctors, who thought she was brain dead (Laureys & Boly, and activation of brain tissue. 2007), did not administer painkillers as they inserted breathing Electrode Any device (such as a wire, needle, or metal plate) used to and feeding tubes down her throat. However, in time Kate dis- electrically stimulate or destroy nerve tissue or to record its activity. covered that she could communicate by blinking her eyes. After a Ablation Surgical removal of tissue. 58 CHAPTER 2 causes changes in behavior or sensory capacity, we also gain insight example, Chapter 6, page 186, explains how changes in brain waves into the purpose of the missing “part.” By using deep lesioning help define various stages of sleep.) (LEE-zhun-ing), structures below the surface of the brain can also be removed. A strong electric current can be used to destroy a small PET Scan amount of brain tissue when delivered via an electrode lowered into A newer technology, called positron emission tomography (PET), a target area inside the brain. (See Figure 2.11.) Again, changes in provides much more detailed images of activity both near the sur- behavior give clues to the function of the affected area. face and below the surface of the brain. A PET scan detects positrons By using ESB, ablation, and deep lesioning, researchers are (subatomic particles) emitted by weakly radioactive glucose (sugar) creating a three-dimensional brain map. This “atlas” shows the as it is consumed by the brain. Because the brain runs on glucose, a sensory, motor, and emotional responses that can be elicited from PET scan shows which areas are using more energy. Higher energy various parts of the brain. It promises to be a valuable guide for use corresponds with higher activity. Thus, by placing positron medical treatment, as well as for exploring the brain (Kalat, 2007; detectors around the head and sending data to a computer, it is pos- Yoshida, 1993). sible to create a moving, color picture of changes in brain activity. To find out what individual neurons are doing, we need to do As you can see in Figure 2.13, PET scans reveal that very specific a microelectrode recording. A microelectrode is an extremely thin brain areas are active when you see, hear, speak, or think. glass tube filled with a salty fluid. The tip of a microelectrode is small enough to detect the electrical activity of a single neuron. Watching the action potentials of just one neuron provides a fasci- bridges nating glimpse into the true origins of behavior. (The action poten- PET scans suggest that different patterns of brain activity tial shown in Figure 2.2 was recorded with a microelectrode.) accompany major psychological disorders, such as depression or schizophrenia. See Chapter 14, pages 473–475. Are any less invasive techniques available for studying brain func- tion? Yes, several techniques allow us to observe the activity of parts of the brain without doing any damage at all. These include the EEG, PET scan, and fMRI. Such techniques allow biopsy- More active brains are good, right? Surprisingly, although we chologists to pinpoint areas in the brain responsible for thoughts, might assume that smart brains are hardworking brains, the reverse feelings, and actions. appears to be true. Using PET scans, psychologist Richard Haier and his colleagues found that the brains of people who perform EEG well on a difficult reasoning test consume less energy than those Electroencephalography (ee-LEK-tro-in-SEF-ah-LOG-ruh-fee) mea- of poor performers (Haier et al., 1988) ( Figure 2.14). Haier sures the waves of electrical activity produced near the surface of the believes this shows that intelligence is related to brain efficiency: brain. Small disk-shaped metal plates are placed on a person’s scalp. Less efficient brains work harder and still accomplish less (Haier, Electrical impulses from the brain are detected by these electrodes White, & Alkire, 2003). We’ve all had days like that! and sent to an electroencephalograph (EEG). The EEG amplifies Is it true that most people use only 10 percent of their brain capac- these very weak signals (brain waves) and records them on a mov- ity? This is one of the lasting myths about the brain. Brain scans ing sheet of paper or a computer screen ( Figure 2.12). Various show that all parts of the brain are active during waking hours. brain-wave patterns can identify the presence of tumors, epilepsy, Obviously, some people make better use of their innate brainpower and other diseases. The EEG also reveals changes in brain activity than others do. Nevertheless, there are no great hidden or untapped during sleep, daydreaming, hypnosis, and other mental states. (For reserves of mental capacity in a normally functioning brain. WDCN/Univ. College London/Photo Researchers, Inc. Seeing Hearing AJPhoto/Photo Researchers, Inc. Speaking Thinking when Figure 2.13 Colored PET scans reveal different patterns of brain activation Figure 2.12 An EEG recording. we engage in different tasks.  Brain and Behavior 59 fMRI A functional MRI (f MRI) uses MRI technology to make brain activity visible. Like PET scans, func- tional MRIs also provide images of activity through- out the brain. For example, if we scanned Carlos Richard Haier, University of California, Irvine Santana while he played his guitar, areas of his brain that control his hands would be highlighted in an fMRI image. Psychiatrist Daniel Langleben and his colleagues have even used fMRI images to tell if a person is lying (Langleben et al., 2005). As Figure 2.15 shows, the front of the brain is more active when a person is lying, rather than telling the truth. This Figure 2.14 In the images you see here, red, orange, and yellow indicate high consumption may occur because it takes extra effort to lie and of glucose; green, blue, and pink show areas of low glucose use. The PET scan of the brain on the left the resulting extra brain activity is detected with shows that a man who solved 11 out of 36 reasoning problems burned more glucose than the man on fMRI. Eventually, fMRI may help us distinguish the right, who solved 33. between lies, false statements made with the inten- tion to deceive, and confabulations, which are false claims made by persons who believe they are telling the truth (Hirstein, 2005; Langleben, Dattilio, & Gutheil, 2006). Clearly, it is just a matter of time until even brighter beacons are flashed into the shadowy inner world of thought. Right side Left side Daniel Langleben, University of Pennsylvania K N O WL E D GE B U I L D E R Brain Research Lie Activation RECITE Truth Activation 1. Which of the following research techniques has the most in com- mon with clinical studies of the effects of brain injuries? a. EEG recording b. deep lesioning c. microelectrode recording d. PET scan Anterior 2. CT scans cannot determine which part of your brain plays a role in speech because CT scans Figure 2.15 Participants were asked to tell the truth or to lie while fMRI images of their brains were taken. When compared with telling the truth (shown in a. use X-rays blue), areas toward the front of the brain were active during lying (shown in red). b. reveal brain structure, not brain activity (Adapted from Langleben et al., 2005.) c. reveal brain activity, not brain structure d. use magnetic fields 3. _________________ links brain structures to brain functions. 4. People only use 10 percent of their brain capacity. T or F? The Cerebral Cortex — My, What REFLECT a Big Brain You Have! Critical Thinking Gateway Question: Why is the human cerebral cortex so important, 5. Deep lesioning is used to ablate an area in the hypothalamus of a and what are its parts? rat. After the operation, the rat seems to lose interest in food and eating. Why would it be a mistake to automatically conclude that the In many ways we are pretty unimpressive creatures. Animals ablated area is a “hunger center”? surpass humans in almost every category of strength, speed, and Relate sensory sensitivity. However, we do excel in intelligence. You suspect that a certain part of the brain is related to risk-taking. How could you use clinical studies, ablation, deep lesioning, and ESB to study the structure? You want to know which areas of the brain’s surface are Deep lesioning Removal of tissue within the brain by use of an electrode. most active when a person sees a face. What methods will you use? ablated area merely relays messages that cause the rat to eat. Electroencephalograph (EEG) A device that detects, amplifies, and ing. It is also possible that hunger originates elsewhere in the brain and the records electrical activity in the brain. of food might be affected, or the rat might simply have difficulty swallow- might explain the apparent loss of appetite. For example, the taste or smell PET scan Positron emission tomography; a computer-generated image Answers: 1. b 2. b 3. Localization of function 4. F 5. Because other factors of brain activity based on glucose consumption in the brain. Functional MRI (fMRI) Functional magnetic resonance imaging that records brain activity. 60 CHAPTER 2 Cortex Although the cortex is only 3 mil- Cerebrum Cerebellum limeters thick (one tenth of an inch), it Neocortex contains 70 percent of the neurons in Olfactory lobe the central nervous system. It is largely responsible for our ability to use language, make tools, acquire complex skills, and live in complex social groups (Gibson, 2002). Without the cortex, we humans wouldn’t be much smarter than toads. Cerebral Hemispheres Fish Brain The cortex is composed of two sides, or Neocortex Cerebellum cerebral hemispheres (half-globes), con- Cerebrum nected by a thick band of fibers called the corpus callosum (KORE-pus kah-LOH- sum) ( Figure 2.17). The left side of the brain mainly controls the right side of the Cerebellum body. Likewise, the right brain mainly Human Brain Olfactory lobe Cerebrum controls left body areas. When our friend Reptile Brain Marge had a stroke, her right hemisphere suffered damage. In Marge’s case, the Figure 2.16 stroke caused some paralysis and loss of sensation on the left side of her body. Does that mean humans have the largest brains? Surpris- Damage to one hemisphere may also cause a curious problem ingly, no. Elephant brains weigh 13 pounds, and whale brains, called spatial neglect. A patient with right hemisphere damage may 19 pounds. At 3 pounds, the human brain seems puny — until pay no attention to the left side of visual space ( Figure 2.18). we compare brain weight to body weight. We then find that Often, the patient will not eat food on the left side of a plate. an elephant’s brain is 1/1,000 of its weight; the ratio for sperm Some even refuse to acknowledge a paralyzed left arm as their whales is 1 to 10,000. The ratio for humans is 1 to 60. If someone own (Hirstein, 2005). If you point to the “alien” arm, the patient tells you that you have a “whale of a brain” be sure to find out if is likely to say, “Oh, that’s not my arm. It must belong to someone they mean size or ratio! else.” (To learn more about strokes, see “A Stroke of Bad Luck.”) So having a larger brain doesn’t necessarily make a person smarter? That’s right. While a small positive correlation exists between Hemispheric Specialization intelligence and brain size, overall size alone does not determine In 1981, Roger Sperry (1914–1994) won a Nobel Prize for his human intelligence ( Johnson et al., 2008; Witelson, Beresh, & remarkable discovery that the right and left brain hemispheres Kigar, 2006). In fact, many parts of your brain are surprisingly perform differently on tests of language, perception, music, and similar to corresponding brain areas in lower animals, such as other capabilities. lizards. It is your larger cerebral (seh-REE-brel or ser-EH-brel) cortex that sets you apart. Corpus Cerebral callosum cortex The cerebral cortex, which looks a little like a giant, wrinkled walnut, consists of the two large hemispheres that cover the upper part of the brain. The two hemispheres are divided into smaller areas known as lobes. Parts of various lobes are responsible for the ability to see, hear, move, think, and speak. Thus, a map of the cerebral cortex is in some ways like a map of human behavior, as we shall see. The cerebral cortex covers most of the brain with a mantle of gray matter (spongy tissue made up mostly of cell bodies). The cor- tex in lower animals is small and smooth. In humans it is twisted and folded, and it is the largest brain structure ( Figure 2.16). The fact that humans are more intelligent than other animals is related to this corticalization (KORE-tih-kal-ih-ZAY-shun), or increase in the size and wrinkling of the cortex. Figure 2.17  Brain and Behavior 61 T HE CLI N I CA L FI LE A Stroke of Bad Luck One morning Bryan Kolb lost his left hand. Strokes and other brain injuries can hit Neurological soft signs, as they are Up early to feed his cat, he could not see his like a thunderbolt. Almost instantly, victims called, include clumsiness, an awkward gait, hand, or anything else to his upper left side. realize that something is wrong. You would, poor hand–eye coordination, and other Kolb, a Canadian neuroscientist, instantly real- too, if you suddenly found that you couldn’t problems with perception or fine muscle ized that he had suffered a right hemisphere move, or feel parts of your body, or see, or control (Stuss & Levine, 2002). These telltale stroke. (Remember, a stroke occurs when an speak. However, some brain injuries are not signs are “soft” in the sense that they aren’t artery carrying blood in the brain bleeds or so obvious. Many involve less dramatic, but direct tests of the brain, like a CT scan or MRI becomes blocked, causing some brain tissue equally disabling, changes in personality, scan. Bryan Kolb initially diagnosed himself