Psychology Notes: The Brain, Neuroplasticity & Tools of Discovery PDF

Module 1.4a The Brain: Neuroplasticity and Tools of Discovery Learning Targets 1.4-1 Explain why psychologists are concerned with human biology. 1.4-2 Explain how biology and experience together enable neuroplasticity. 1.4-3 Compare and contrast several techniques for studying the brain’s connection...

Module 1.4a The Brain: Neuroplasticity and Tools of Discovery Learning Targets 1.4-1 Explain why psychologists are concerned with human biology. 1.4-2 Explain how biology and experience together enable neuroplasticity. 1.4-3 Compare and contrast several techniques for studying the brain’s connections to behavior and mind. 1.4-1 Why are psychologists concerned with human biology? Our understanding of how the brain gives birth to the mind has come a long way. The ancient Greek physician Hippocrates correctly located the mind in the brain. His contemporary, the philosopher Aristotle, believed the mind was sited in the heart, which pumps warmth and vitality to the body. The heart remains our symbol for love, but science has long since overtaken philosophy on this issue: It’s your brain, not your heart, that falls in love. In the early 1800s, German physician Franz Gall proposed that phrenology, studying bumps on the skull, could reveal a person’s mental abilities and character traits (Figure 1.4-1). At one point, Britain was home to 29 phrenological societies. Phrenologists also traveled North America to give skull readings (Dean, 2012; Hunt, 359 1993). Using a false name, humorist Mark Twain put one famous phrenologist to the test. “He found a cavity [and] startled me by saying that that cavity represented the total absence of the sense of humor!” Three months later, Twain sat for a second reading, this time identifying himself. Now “the cavity was gone, and in its place was … the loftiest bump of humor he had ever encountered in his life-long experience!” (Lopez, 2002). Today, the “science” of phrenology reminds us of our need to engage in critical thinking and scientific analysis. Phrenology did at least succeed in focusing attention on the localization of function — the idea that various brain regions have particular functions. Figure 1.4-1 A wrongheaded theory (a) Despite scientists’ initial acceptance of Franz Gall’s speculations, bumps on the skull tell us nothing about the brain’s underlying functions. Nevertheless, some of his assumptions have held true. Though they are not the functions Gall proposed, different parts of the brain do control different aspects of behavior, as suggested in (b) (from The Human Brain Book), and as you will see throughout this unit. 360  AP® Science Practice Research Unlike phrenologists, psychological scientists take an empirical, or scientifically derived approach to studying the brain. As Unit 0 explained, they use an evidence-based method that draws on observation and experimentation. Today, we are living in a time Gall could only dream about. Biological psychologists use advanced technologies to study the links between biological (genetic, neural, hormonal) and psychological processes. They and other researchers working from a biological perspective are announcing discoveries about the interplay of our biology and our behavior and mind at an exhilarating pace. Within little more than the past century, researchers seeking to understand the biology of the mind have discovered that: Among the body’s cells are neurons that conduct electricity and “talk” to one another by sending chemical messages across a synapse (see Module 1.3). Our experiences wire our adaptive brain. Specific brain systems serve specific functions (though not the functions Gall supposed). We integrate information processed in these different brain systems to construct our experiences of sights and sounds, 361  meanings and memories, pain and passion. biological psychology the scientific study of the links between biological (genetic, neural, hormonal) and psychological processes. Some biological psychologists call themselves behavioral neuroscientists, neuropsychologists, behavior geneticists, physiological psychologists, or biopsychologists. We have also realized that we are each a system composed of subsystems that are in turn composed of even smaller subsystems. Tiny cells organize to form body organs. These organs form larger systems for digestion, circulation, and information processing. And those systems are part of an even larger system — the individual, who in turn is a part of a family, a community, and a culture. Thus, we are biopsychosocial systems. To understand our behavior, we need to study how these biological, psychological, and social-cultural systems work and interact, and how they shape us over time. The biopsychosocial approach integrates these three levels of analysis — the biological, psychological, and social-cultural (Figure 1.4-2). biopsychosocial approach an integrated approach that incorporates biological, psychological, and social-cultural levels of analysis. levels of analysis the differing complementary views, from biological to psychological to social-cultural, for analyzing any given phenomenon. 362  Figure 1.4-2 Biopsychosocial approach This integrated viewpoint incorporates various levels of analysis and offers a more complete picture of any given behavior or mental process. Cultural Awareness In the biopsychosocial approach, culture — the enduring beliefs, ideas, attitudes, values, and traditions shared by a group — is an important component in understanding human behavior. It plays a role equal to those of the biological and psychological systems. Can you think of some ways your culture influences your behavior? AP® Exam Tip You will see versions of Figure 1.4-2 throughout the text. Spend some time now familiarizing yourself with how the figure’s three viewpoints might contribute to behavior or mental processes, the very foundation of psychology. As we’ve seen, we are formed by both ancient evolution and our fluctuating hormones — but we are also shaped by our enduring 363 cultures, by our daily experiences, and by our immediate neural activity (Sapolsky, 2017). Consider, for example, the brain’s ability to rewire itself as it adapts to experience. The Power of Neuroplasticity 1.4-2 How do biology and experience together enable neuroplasticity? Your brain is sculpted not only by your genes but also by your life. Under the surface of your awareness, your brain is constantly changing, building new pathways as it adjusts to little mishaps and new experiences. This change is called neuroplasticity. Neuroplasticity is greatest in childhood, but it persists throughout life (Lindenberger & Lövdén, 2019). neuroplasticity the brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience. To see neuroplasticity at work, consider London’s taxi driver trainees. They spend years learning and remembering the city’s 25,000 street locations and connections. For the half who pass the difficult final test, big rewards are in store: not only a better income but also an enlarged hippocampus, one of the brain’s memory centers that processes spatial memories. London’s bus drivers, who navigate a smaller set of roads, gain no similar neural rewards (Maguire et al., 2000, 2006; Woollett & Maguire, 2012). 364  The mind’s eye Daniel Kish, who is completely blind, enjoys going for walks in the woods. To stay safe, he uses echolocation — the same navigation method used by bats and dolphins. Blind echolocation experts such as Kish engage the brain’s visual centers to navigate their surroundings (Thaler et al., 2011, 2014). Although Kish is blind, his flexible brain helps him “see.” We also see neuroplasticity in well-practiced pianists, who have a larger-than-usual auditory cortex area, a sound-processing region (Bavelier et al., 2000; Pantev et al., 1998). Practice likewise sculpts the brains of ballerinas, jugglers, and unicyclists (Draganski et al., 2004; Hänggi et al., 2010; Weber et al., 2019). Your brain is a work in progress. The brain you were born with is not the brain you will die with. Even limited practice times may produce neural benefits. If you spend 45 minutes learning how to play the 365 piano, as did non-piano-playing participants in one study, you may grow your motor learning–related brain areas (Tavor et al., 2020). Even an hour of learning produces subtle brain changes (Brodt et al., 2018). Remember that the next time you attend class! Neuroplasticity is part of what makes humans exceptional (Gómez- Robles et al., 2015). Think of how much the world has changed over the past 50 years, and how much more it will change in the next 50. Our neuroplasticity enables us, more than other species, to adapt to our changing world (Roberts & Stewart, 2018). Marian Diamond (1926–2017) This ground- breaking neuroscientist explored how experience changes the brain. AP® Science Practice Check Your Understanding Examine the Concept Explain neuroplasticity. 366  Explain how learning a new skill affects the structure of our brain. Apply the Concept Which skills did you practice the most as a child — sports, music, cooking, video gaming? Explain how this affected your brain development and how your brain will continue to develop with new learning and new skills. Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. Tools of Discovery: Having Our Head Examined 1.4-3 How do neuroscientists study the brain’s connections to behavior and mind? The mind seeking to understand the brain — that is among the ultimate scientific challenges. And so it will always be. To paraphrase cosmologist John Barrow, a brain simple enough to be fully understood is too simple to produce a mind able to understand it. When you think about your brain, you’re thinking with your brain — by releasing billions of neurotransmitter molecules across trillions of synapses. Indeed, say neuroscientists, the mind is what the brain does. In “The Adventure of the Mazarin Stone,” Sherlock Holmes declared: “I am a brain, Watson. The rest of me is a mere appendix.” Would you agree? 367 For most of human history, scientists had no tools high-powered yet gentle enough to reveal a living brain’s activity. Early case studies helped localize some brain functions. Damage to one side of the brain often caused numbness or paralysis on the opposite side, suggesting that the body’s right side is wired to the brain’s left side, and vice versa. Damage to the back of the brain disrupted vision, and damage to the left-front part of the brain produced speech difficulties. Gradually, these early explorers were mapping the brain. Now, a new generation of neural mapmakers is charting the known universe’s most amazing organ. Scientists can selectively lesion (destroy) tiny clusters of normal or defective brain cells, observing any effect on brain function. In the laboratory, such studies have revealed, for example, that damage to one area of a rat’s hypothalamus reduces eating to the point of starvation, whereas damage to another area produces overeating. lesion [LEE-zhuhn] tissue destruction. Brain lesions may occur naturally (from disease or trauma), during surgery, or experimentally (using electrodes to destroy brain cells). Today’s neuroscientists can also stimulate various brain parts — electrically, chemically, or magnetically — and note the effect. Depending on the stimulated brain part, people may — to name a few examples — giggle, hear voices, turn their head, feel themselves falling, or have an out-of-body experience (Selimbeyoglu & Parvizi, 2010). 368  AP® Science Practice Research Electrically stimulating a brain part to note its effect on behavior implies an experimental research design. You cannot infer causality from non-experimental designs. Scientists can even snoop on the messages transmitted by individual neurons. With tips small enough to detect the electrical pulse in a single neuron, modern electrodes can, for example, now detect exactly where the information goes in a rat’s brain when someone tickles its belly (Ishiyama & Brecht, 2017). They can also eavesdrop on the chatter of billions of neurons and see color representations of the brain’s energy-consuming activity. Promising new tools include optogenetics, a technique that allows neuroscientists to control the activity of individual neurons (Boyden, 2014). By programming neurons to become receptive to light, researchers can examine the biological bases of sensations, fear, depression, and substance use disorders (Dygalo & Shishkina, 2019; Firsov, 2019; Juarez et al., 2019; Nikitin et al., 2019). Right now, your mental activity is emitting telltale electrical, metabolic, and magnetic signals that would enable neuroscientists to observe your brain at work. Electrical activity in your brain’s billions of neurons sweeps in regular waves across its surface. An EEG (electroencephalogram) is an amplified readout of such waves. Researchers record the brain waves through a shower-cap-like hat that is filled with electrodes covered with a conductive gel. Studying 369 an EEG of the brain’s activity is like studying a blender’s motor by listening to its hum. Researchers may lack direct access to the brain, but they can present a stimulus repeatedly and have a computer filter out brain activity unrelated to the stimulus. What remains is the electrical wave evoked by the stimulus. EEG (electroencephalogram) an amplified recording of the waves of electrical activity sweeping across the brain’s surface. These waves are measured by electrodes placed on the scalp. A related technique, MEG (magnetoencephalography), measures magnetic fields from the brain’s natural electrical activity. To isolate the brain’s magnetic fields, researchers create special rooms that cancel out other magnetic signals, such as the Earth’s magnetic field. Participants sit underneath a head coil that resembles a salon hair dryer. While participants complete activities, tens of thousands of neurons generate electrical pulses, which in turn create magnetic fields. The speed and strength of the magnetic fields enable researchers to understand how certain tasks influence brain activity (Samuelsson et al., 2020). MEG (magnetoencephalography) a brain-imaging technique that measures magnetic fields from the brain’s natural electrical activity. Newer neuroimaging techniques give us a superhero-like ability to see inside the living brain. For example, the CT (computed tomography) scan examines the brain by taking X-ray photographs that can reveal brain damage. Another such tool, PET (positron emission tomography) (Figure 1.4-3), depicts brain activity by 370 showing each brain area’s consumption of its chemical fuel, the sugar glucose. Active neurons gobble glucose. Our brain, though only about 2 percent of our body weight, consumes 20 percent of our calorie intake. After a person receives temporarily radioactive glucose, the PET scan can track the gamma rays released by this “food for thought” as a task is performed. Rather like weather radar showing rain activity, PET-scan “hot spots” show the most active brain areas as the person does mathematical calculations, looks at images of faces, or daydreams. CT (computed tomography) scan a series of X-ray photographs taken from different angles and combined by computer into a composite representation of a slice of the brain’s structure. PET (positron emission tomography) a technique for detecting brain activity that displays where a radioactive form of glucose goes while the brain performs a given task. 371  Figure 1.4-3 The PET scan In MRI (magnetic resonance imaging) brain scans, the person’s head is put in a strong magnetic field, which aligns the spinning atoms in brain molecules. Then, a radio-wave pulse momentarily disorients the atoms. When the atoms return to their normal spin, they emit signals that provide a detailed picture of soft tissues, including the brain. MRI scans have revealed a larger-than-average neural area in the left hemisphere of musicians who display perfect pitch (Yuskaitis et al., 2015). They have also revealed enlarged ventricles — fluid-filled brain areas (marked by the red arrows in Figure 1.4-4) — in some people with schizophrenia. MRI (magnetic resonance imaging) a technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. MRI scans show brain anatomy. Figure 1.4-4 MRI scans of individuals without schizophrenia (a) and with schizophrenia (b) Note the enlarged ventricle — the fluid-filled brain region at the tip of the arrow in the 372  image — in the brain of the person with schizophrenia (b). A special application of MRI — fMRI (functional MRI) — can reveal the brain’s functioning as well as its structure. Where the brain is especially active, blood goes. By comparing successive MRI scans, researchers can watch as specific brain areas activate, showing increased oxygen-laden blood flow. As a person looks at a scene, for example, the fMRI machine detects blood rushing to the back of the brain, which processes visual information. Another tool, functional near-infrared spectroscopy (fNIRS), shines infrared light on blood molecules to identify brain activity. The fNIRS equipment can fit in a large backpack, enabling researchers to study the biology of mind in difficult-to-reach populations (Burns et al., 2019; Perdue et al., 2019). Table 1.4-1 compares imaging techniques. fMRI (functional MRI) a technique for revealing blood flow and, therefore, brain activity by comparing successive MRI scans. fMRI scans show brain function as well as structure. table 1.4-1 Common Types of Neural Measures Name How Does It Work? Sample Finding Electroencephalography Electrodes placed on the Symptoms of depression (EEG) scalp measure electrical and anxiety correlate with activity in neurons. increased activity in the right frontal lobe, a brain area associated with behavioral withdrawal and negative emotion (Thibodeau et al., 2006). 373 Magnetoencephalography A head coil records magnetic Soldiers with posttraumatic (MEG) fields from the brain’s stress disorder (PTSD), natural electrical currents. compared with soldiers who do not have PTSD, show stronger magnetic fields in the visual cortex when they view trauma-related images (Todd et al., 2015). Computed tomography (CT) X-rays of the head generate Children’s brain injuries, images that may locate brain shown in CT scans, predict damage. impairments in their intelligence and memory processing (Königs et al., 2017). Positron emission Tracks where in the brain a Monkeys with an anxious tomography (PET) temporarily radioactive form temperament have brains of glucose goes while the that use more glucose in person given it performs a regions related to fear, task. memory, and expectations of reward and punishment (Fox et al., 2015). Magnetic resonance imaging People sit or lie down in a People with a history of (MRI) chamber that uses magnetic violence tend to have fields and radio waves to smaller frontal lobes, provide a map of brain especially in regions that aid structure. moral judgment and self- control (Glenn & Raine, 2014). Functional magnetic Measures blood flow to brain Years after surviving a near resonance imaging (fMRI) regions by comparing plane crash, passengers who continuous MRI scans. viewed material related to their trauma showed greater activation in the brain’s fear, 374  memory, and visual centers than when they watched footage related to the 9/11 terrorist attacks (Palombo et al., 2015). Understanding the non-WEIRD brain Most neuroscience research studies people from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) populations (Falk et al., 2013). Using functional near-infrared spectroscopy (fNIRS), the researchers shown here were able to identify brain areas involved in persuasion among a Jordanian sample (Burns et al., 2019). Such snapshots of the brain’s activity provide new insights into how the brain divides its labor and reacts to changing needs. A mountain of recent fMRI studies has revealed which brain areas are most active when people feel pain or rejection, listen to angry voices, think about scary things, feel happy, or become sexually aroused. The technology enables a very basic sort of mind reading. One neuroscience team scanned 129 people’s brains as they did eight 375 different mental tasks (such as reading, gambling, or rhyming). Later, they were able, with 80 percent accuracy, to identify which of these mental activities the study participants had been doing (Poldrack et al., 2018). You’ve undoubtedly seen pictures of colorful “lit-up” brain regions with accompanying headlines, such as “your brain on music.” Although brain areas don’t actually light up, vivid brain scan images seem impressive. In fact, people have rated scientific explanations as more believable and interesting when they contain neuroscience (Fernandez-Duque et al., 2015; Im et al., 2017). But “neuroskeptics” caution against overblown claims about any ability to predict customer preferences, to detect lies, and to foretell crime based on neuroscience (Schwartz et al., 2016). Neuromarketing, neuroleadership, neurolaw, and neuropolitics are often neurohype. Imaging techniques illuminate brain structure and activity, and sometimes they can help us test different theories of behavior (Mather et al., 2013). But given that all human experience is brain based, it’s no surprise that different brain areas become active when one listens to a lecture or lusts for a lover. Today’s techniques for peering into the thinking, feeling brain are doing for psychology what the microscope did for biology and the telescope did for astronomy. European researchers have undertaken a $1 billion Human Brain Project (Salles et al., 2019). Another project is exploring brain aging from age 3 to 96 (Pomponio et al., 2020). These massive undertakings harness the collective power of hundreds of scientists from dozens of countries (Thompson et al., 376 2020) (Figure 1.4-5). “Individually, we contribute little or nothing to the truth,” said Aristotle. “By the union of all a considerable amount is amassed.” Figure 1.4-5 Beautiful brain connections The Human Connectome Project is using cutting-edge diffusion tensor imaging MRI methods to map the brain’s interconnected network of neurons (Glasser et al., 2016; Wang & Olson, 2018). Such efforts have led to the creation of a new brain map with 100 neural centers not previously described (Glasser et al., 2016). Scientists created this multicolored “symphony” of neural fibers transporting water through different brain regions. To learn about the neurosciences now is like studying world geography when Magellan explored the seas. This truly is the golden age of brain science. 377 AP® Science Practice Check Your Understanding Examine the Concept Match the scanning technique (i–iii) with the correct description (a–c). Technique: Description: i. fMRI scan a. Tracks radioactive glucose to reveal brain activity. ii. PET scan b. Tracks successive images of brain tissue to show brain function. iii. MRI scan c. Uses magnetic fields and radio waves to show brain anatomy. Apply the Concept Compare and contrast each of the common types of neural measures. Were you surprised to learn that there are so many technologies to study the brain’s structures and functions? Which techniques do you find most interesting? Why? Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. 378  Module 1.4a REVIEW 1.4-1 Why are psychologists concerned with human biology? Researchers working from a biological perspective study the links between our biology and our behavior. We are biopsychosocial systems: biological, psychological, and social-cultural factors interact to influence behavior. 1.4-2 How do biology and experience together enable neuroplasticity? Our brain’s neuroplasticity allows us to build new neural pathways as we adjust to new experiences. Our brain is a work in progress, changing with the focus and practice we devote to new ventures. Neural plasticity is strongest in childhood, but it continues throughout life. 1.4-3 How do neuroscientists study the brain’s connections to behavior and mind? Case studies and lesioning first revealed the general effects of brain damage. Modern electrical, chemical, or magnetic stimulation also reveals aspects of information processing in the brain. 379  CT and MRI scans show anatomy. EEG, MEG, PET, and fMRI (functional MRI) recordings reveal brain function. AP® Practice Multiple Choice Questions 1. Researchers wanted to determine the brain waves present when individuals were sleeping. They placed electrodes on the scalps of 100 volunteers, and then asked the volunteers to sleep in the laboratory each night for one week. The researchers obtained recordings of the electrical activity across the volunteers’ brain surfaces. Which of the following represents the operational definition of the dependent variable in this study? a. MRI readings b. CT readings c. MEG readings d. EEG readings 2. Dr. Ultrone uses a technique to measure glucose consumption as an indicator of brain activity. What is the name of this technique? a. MRI 380  b. fMRI c. PET d. EEG 3. Zoey did a report on the brain’s ability to change in response to both experience and damage. What was her report about? a. Neurostimulation b. Neuroplasticity c. Neurobiology d. Neuropsychology 4. When Amita is in a car accident, her neurologist, Dr. Lang, suspects she has sustained an injury to the back of her brain. “Can you check with an EEG?” asks Amita’s brother. Dr. Lang explains that an EEG is not the best method for assessing this injury, because a. an EEG only provides images of how the brain consumes glucose. b. an EEG only provides images of brain-wave activity. c. an EEG only provides still images of the brain. 381  d. an EEG only provides stimulation to one region of the brain. 5. Dr. Translucent measures the brain’s electrical activity via magnetic fields, using a(n) a. CT. b. EEG. c. MEG. d. PET. Use the following text to answer questions 6 and 7: Dr. Ludwikowski was interested in studying effects of stress on the brain. She randomly assigned 10 middle-aged participants to experience stress by placing them in a room with a loud, unpleasant noise. The other 10 middle-aged participants were placed in a room with no noise. She then used an fMRI to compare participants’ brain activity. 6. In this study, what was Dr. Ludwikowski’s operational definition of her dependent variable? a. fMRI results b. Noise c. Stress 382  d. Age 7. In Dr. Ludwikowski’s study, the participants in the room with no noise served as the a. independent variable. b. confederates. c. control group. d. placebo group. 383 Module 1.4b The Brain: Brain Regions and Structures Learning Targets 1.4-4 Explain how the hindbrain, midbrain, and forebrain apply to behavior and mental processes. 1.4-5 Describe the structures of the brainstem, and explain the functions of the brainstem, thalamus, reticular formation, and cerebellum. 1.4-6 Explain the limbic system’s structures and functions. 1.4-7 Describe the four lobes that make up the cerebral cortex and explain the functions of the motor cortex, somatosensory cortex, and association areas. 1.4-4 What are the hindbrain, midbrain, and forebrain? Vertebrate brains have three main divisions. The hindbrain contains brainstem structures that direct essential survival functions, such as breathing, sleeping, arousal, coordination, and balance. The midbrain, atop the brainstem, connects the hindbrain with the forebrain; it also controls some movement and transmits information that enables our seeing and hearing. The forebrain manages complex cognitive activities, sensory and associative functions, and voluntary motor activities (Figure 1.4-6). Individual organisms’ brains have evolved to best suit their environment (Cesario et al., 2020). We humans, for example, have extremely well- developed forebrains, allowing us an unparalleled ability to make complex decisions and judgments. Predatory sharks have complex 384 hindbrains, supporting their impressive ability to chase down prey (Yopak et al., 2010). hindbrain consists of the medulla, pons, and cerebellum; directs essential survival functions, such as breathing, sleeping, and wakefulness, as well as coordination and balance. midbrain found atop the brainstem; connects the hindbrain with the forebrain, controls some motor movement, and transmits auditory and visual information. forebrain consists of the cerebral cortex, thalamus, and hypothalamus; manages complex cognitive activities, sensory and associative functions, and voluntary motor activities. Figure 1.4-6 Brain divisions: forebrain, midbrain, hindbrain In the hindbrain, the brainstem (including the pons and medulla) is an extension of the spinal cord. The thalamus is attached to the top of the brainstem. The reticular formation passes through both structures. 385  AP® Exam Tip Your authors are about to take you on a journey through your brain. Focus on the name of each part, its location within the brain, and what it does. Then it’s time to practice, practice, practice. The brain structures have been on previous AP® exams. The Brainstem 1.4-5 Which structures make up the brainstem, and what are the functions of the brainstem, thalamus, reticular formation, and cerebellum? The brainstem is the brain’s innermost region. Its base is the medulla, the slight swelling in the spinal cord just after it enters the skull (see Figure 1.4-6). Here lie the controls for your heartbeat and breathing. As some brain-damaged patients in a vegetative state illustrate, we do not need a conscious mind to orchestrate our heart’s pumping and lungs’ breathing. The brainstem handles those tasks. Just above the medulla sits the pons, which helps coordinate movements and control sleep. brainstem the central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions. medulla [muh-DUL-uh] the hindbrain structure that is the brainstem’s base; controls heartbeat and breathing. If a researcher severs a cat’s brainstem from the rest of its brain, the animal will still breathe and live — and even run, climb, and groom 386 (Klemm, 1990). But cut off from its midbrain and forebrain, the cat won’t purposefully run or climb to get food. AP® Science Practice Research Some techniques, such as severing the brainstem, are unethical to use on humans. Researchers therefore rely on animal studies. As Unit 0 explained, the American Psychological Association has ethical guidelines for psychologists’ use of animals. The brainstem is also a crossover point, where most nerves to and from each side of the brain connect with the body’s opposite side (Figure 1.4-7). This peculiar cross-wiring — the brain’s contralateral hemispheric organization — is but one of the brain’s many surprises. 387 Figure 1.4-7 The body’s wiring 388 The Thalamus Sitting atop the brainstem is the forebrain’s thalamus, a pair of egg- shaped structures that act as the brain’s sensory control center (see Figure 1.4-6). The thalamus receives information from all the senses except smell, and routes that information to the brain regions that deal with seeing, hearing, tasting, and touching. The thalamus also receives some of the replies from those regions, which it then directs to the medulla and to the hindbrain’s cerebellum. Think of the thalamus as being to sensory information what Seoul is to South Korea’s trains: a hub through which traffic passes en route to various destinations. thalamus [THAL-uh-muss] the forebrain’s sensory control center, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla. The Reticular Formation Inside the brainstem, between your ears, lies the reticular (“netlike”) formation. This nerve network, which is governed by the reticular activating system, extends from the spinal cord right up through the thalamus. As the spinal cord’s sensory input flows up to the thalamus, some of it travels through the reticular formation, which filters incoming stimuli and relays important information to other brain areas. reticular formation a nerve network that travels through the brainstem into the thalamus; it filters information and plays an important role in controlling arousal. 389 The reticular formation also controls arousal — our state of alertness — as Giuseppe Moruzzi and Horace Magoun discovered in 1949. When they electrically stimulated a sleeping cat’s reticular formation, it almost instantly produced an awake, alert animal. When Magoun severed a cat’s reticular formation without damaging nearby sensory pathways, the effect was equally dramatic: The cat lapsed into a coma from which it never awakened. The Cerebellum Extending from the rear of the brainstem is the hindbrain’s baseball- sized cerebellum; its name means “little brain,” which is what its two wrinkled halves resemble (Figure 1.4-8). The cerebellum (along with the basal ganglia — deep brain structures involved in motor movement) enables nonverbal and skill (or procedural) learning. With assistance from the pons, it also coordinates voluntary movement. When a soccer player masterfully controls the ball, give their cerebellum some credit. Under alcohol’s influence, coordination suffers. And if you injured your cerebellum, you would have difficulty walking, keeping your balance, or texting a friend. Your movements would be jerky and exaggerated. Gone would be any dreams of being a dancer or guitarist. cerebellum [sehr-uh-BELL-um] the hindbrain’s “little brain” at the rear of the brainstem; its functions include processing sensory input, coordinating movement output and balance, and enabling nonverbal learning and memory. 390  Figure 1.4-8 The brain’s organ of agility Hanging at the back of the brain, the cerebellum coordinates our voluntary movements, as when soccer player Mallory Pugh controls the ball. This little brain — which actually contains more than half your brain’s neurons — operates just outside your awareness. Quickly answer these questions: How long have you been reading this text? Do your clothes feel loose or tight? How’s your mood? You probably answered easily, thanks to your cerebellum. * Note: The brain functions we’ve discussed so far all occur without any conscious effort. This illustrates another of our recurring themes: Our brain processes most information outside of our awareness. We are aware of the results of our brain’s labor — say, our current visual experience — but not how we construct the visual image. 391 Likewise, whether we are asleep or awake, our brainstem manages its life-sustaining functions, freeing our conscious brain regions to think, talk, dream, or savor a memory. AP® Science Practice Check Your Understanding Examine the Concept Explain some brain functions that happen without any conscious effort. The is a crossover point where nerves from the left side of the brain are mostly linked to the right side of the body, and vice versa. Apply the Concept Are you surprised to learn about all the information processing that happens automatically, without your knowledge? Why or why not? In which brain region would damage be most likely to (a) disrupt your ability to jump rope? (b) disrupt your ability to hear? (c) leave you in a coma? (d) cut off the very breath and heartbeat of life? Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. The Limbic System 1.4-6 What are the limbic system’s structures and functions? 392 A skeleton walks into a café. “What would you like?” asks the barista. The skeleton replies, “I’ll take a latte and a mop.” We can thank our limbic system for that wonderful emotion when we enjoy a joke. This system, which is associated with emotions, drives, and memory formation, contains the amygdala, hypothalamus, hippocampus, thalamus, and pituitary gland (Figure 1.4-9). limbic system neural system located mostly in the forebrain — below the cerebral hemispheres — that includes the amygdala, hypothalamus, hippocampus, thalamus, and pituitary gland; associated with emotions and drives. Figure 1.4-9 The limbic system This neural system is located mostly in the forebrain. The limbic system’s hypothalamus controls the nearby pituitary gland. 393 The Amygdala The amygdala — two lima-bean–sized neural clusters — enables aggression and fear. In 1939, psychologist Heinrich Klüver and neurosurgeon Paul Bucy surgically removed a rhesus monkey’s amygdala, turning the normally ill-tempered animal into the mellowest of creatures. So, too, with humans. People with amygdala lesions often display reduced arousal to fear-and anger-arousing stimuli (Berntson et al., 2011). One woman with an amygdala lesion, patient S. M., has been called “the woman with no fear,” even if being threatened with a gun (Feinstein et al., 2013). amygdala [uh-MIG-duh-la] two lima-bean–sized neural clusters in the limbic system; linked to emotion. What, then, might happen if we electrically stimulated the amygdala of a normally placid domestic animal, such as a cat? Do so in one spot and the cat prepares to attack, hissing with its back arched, its pupils dilated, its hair on end. Move the electrode only slightly within the amygdala, cage the cat with a small mouse, and now it cowers in terror. 394 These and other experiments have confirmed the amygdala’s role in fear and rage. Monkeys and humans with amygdala damage become less fearful of strangers (Harrison et al., 2015). Other studies link criminal behavior with amygdala dysfunction (Dotterer et al., 2017; Ermer et al., 2012a). AP® Science Practice Research Notice the phrase, “other studies link criminal behavior with amygdala dysfunction.” Because researchers cannot ethically manipulate the variable of amygdala dysfunction, they cannot draw causal conclusions. This is an important point in psychology: Correlation does not equal causation. But we must be careful. The brain is not neatly organized into structures that correspond to our behavior categories. The amygdala is engaged with other mental phenomena as well. And when we feel 395 afraid or act aggressively, neural activity occurs in many areas of our brain — not just the amygdala. If you destroy a car’s battery, the car won’t run. But the battery is merely one link in an integrated system. The Hypothalamus Just below (hypo) the thalamus is the hypothalamus (Figure 1.4-10), an important link in the command chain governing bodily maintenance. Some neural clusters in the hypothalamus influence hunger; others regulate thirst, body temperature, and sexual behavior. Together, they help maintain a steady (homeostatic) internal state. hypothalamus [hi-po-THAL-uh-muss] a limbic system neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system, and is linked to emotion and reward. Figure 1.4-10 The hypothalamus This small but important structure, colored yellow/orange in this MRI scan, helps keep 396  the body’s internal environment in a steady state. To monitor your body state, the hypothalamus tunes into your blood chemistry and any incoming orders from other brain parts. For example, if it picks up signals from your brain’s cerebral cortex that you are thinking about sex, your hypothalamus will secrete hormones. These hormones will, in turn, trigger the pituitary, which controls your endocrine system (Figure 1.4-9) to influence your sex glands to release their hormones. These hormones will intensify the thoughts of sex in your cerebral cortex. (Note the interplay between the nervous and endocrine systems: The brain influences the endocrine system, which in turn influences the brain.) A remarkable discovery about the hypothalamus illustrates how progress in science often occurs — when curious, open-minded investigators make an unexpected observation. Two young McGill University neuropsychologists, James Olds and Peter Milner (1954), were trying to implant an electrode in a rat’s reticular formation when they made a magnificent mistake: They placed the electrode incorrectly (Olds, 1975). Strangely, as if seeking more stimulation, the rat kept returning to the location where it had been stimulated by this misplaced electrode. On discovering that they had actually placed the device in a region of the hypothalamus, Olds and Milner realized they had stumbled upon a brain center that provides pleasurable rewards. 397 Later experiments located other “pleasure centers” (Olds, 1958). (What the rats actually experience only they know, and they aren’t telling. Rather than attribute human feelings to rats, today’s scientists refer to reward centers.) Just how rewarding are these reward centers? Enough to cause rats to self-stimulate these brain regions more than 1000 times per hour. In other species, including dolphins and monkeys, researchers later discovered other limbic system reward centers, such as the nucleus accumbens in front of the hypothalamus (Hamid et al., 2016). Animal research has also revealed both a general dopamine-related reward system and specific centers associated with the pleasures of eating, drinking, and sex. Animals, it seems, come equipped with built-in systems that reward activities essential to survival. As neuroscientist Candice Pert (1986) observed, “If you were designing a robot vehicle to walk into the future and survive, … you’d wire it up so that behavior that ensured the survival of the self or the species — like sex and eating — would be naturally reinforcing.” AP® Science Practice Data Interpretation Number of Presses Rats receiving reward center Rats not receiving reward center activation activation 398  Trial 204 202 1 Trial 813 250 2 Trial 857 300 3 Trial 900 156 4 Trial 1001 158 5 This module describes research on rats that led to the identification of the hypothalamus as a reward center in the brain. Consider the data set above. Describe the general difference in number of presses between the groups represented in this table. Describe the trends in the data within each group. Calculate the mean for each group. Is the variable “number of presses” qualitative or quantitative? Explain. Remember, you can always revisit Unit 0 to review information related to psychological research. Do humans have limbic centers for pleasure? Some evidence indicates we do. When we meet likable people or read affirming messages from friends, our brain bursts with reward center activity (Inagaki et al., 2019; Zerubavel et al., 2018). But when one neurosurgeon implanted electrodes in violent patients’ reward center areas, the patients reported only mild pleasure. Unlike Olds and Milner’s rats, the patients were not driven to a frenzy (Deutsch, 1972; Hooper & Teresi, 1986). Stimulating the brain’s “hedonic hot 399 spots” (its reward circuits) produces more desire than pure enjoyment (Kringelbach & Berridge, 2012). Experiments have also revealed the effects of a dopamine-related reward system in people. For example, experimentally boosting dopamine levels increases the pleasurable “chills” response to a favorite piece of music, whereas reducing dopamine levels decreases musical-related pleasure (Ferreri et al., 2019). Some researchers believe that many disordered behaviors may stem from malfunctions in the natural brain systems for pleasure and well- being. People genetically predisposed to this reward deficiency syndrome may crave whatever provides that missing pleasure or relieves negative feelings, such as aggression, rich food, or drugs and alcohol (Blum et al., 1996, 2014; Chester et al., 2016). The Hippocampus The hippocampus is a curved brain structure that processes conscious, explicit memories. Humans who lose their hippocampus to surgery or injury also lose their ability to form new memories of facts and events (Clark & Maguire, 2016). Those who survive a hippocampal brain tumor in childhood struggle to remember new information in adulthood (Jayakar et al., 2015). National Football League (NFL) players who experience one or more loss-of- consciousness concussions may later have a shrunken hippocampus and poor memory (Strain et al., 2015; Tharmaratnam et al., 2018). Hippocampus size and function decrease as we grow older, which furthers cognitive decline (O’Callaghan et al., 2019; see Module 3.2). 400 Modules 2.5 and 2.7 explain how our two-track mind uses the hippocampus to process our memories. hippocampus a neural center in the limbic system that helps process explicit (conscious) memories — of facts and events — for storage. Are football players’ brains protected? When researchers analyzed the brains of 111 deceased National Football League players, 99 percent showed signs of degeneration related to frequent head trauma (Mez et al., 2017). In 2017, NFL player Aaron Hernandez (#81) died by suicide while imprisoned for murder. An autopsy revealed that his brain, at age 27, was already showing advanced degeneration (Kilgore, 2017). In hopes of protecting players, some teams use more protective gear and portable brain-imaging tools (Canadian Press, 2018). * 401 Figure 1.4-11 locates the brain areas we’ve discussed, as well as the cerebral cortex — the body’s ultimate control and information- processing center, to which we will turn next — and the corpus callosum, which connects the two brain hemispheres (see Module 1.4c). Figure 1.4-11 Brain structures and their functions AP® Science Practice Check Your Understanding Examine the Concept Explain the functions of the key structures of the limbic system. 402 Apply the Concept Why do you think our brain evolved into so many interconnected structures with varying functions? Explain how the pons, hippocampus, and amygdala are influencing you as you read this text. Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. AP® Science Practice Exploring Research Methods & Design As a result of research on traumatic brain injuries, the NFL implemented new procedures to protect players who experience concussions, including neuropsychological tests for players before they can return to play after sustaining a head injury. Research shows that repeated concussions are associated with increased depression, impaired judgment, memory loss, and, in later life, dementia. Researchers autopsied the brains of former players and found neurodegeneration at a much higher rate than in the general population: A study of 111 deceased NFL players found that 99 percent had neurodegeneration (Mez et al., 2017). Determine which research design was employed in the 2017 study — correlational or experimental. Explain the difference between the sample and the population in this study. Explain what conclusions you can and cannot draw from this study. What ethical guidelines, if any, would prevent you from using random assignment when studying this topic? Remember, you can always revisit Unit 0 to review information related to psychological research. 403 The Cerebral Cortex 1.4-7 What four lobes make up the cerebral cortex, and what are the functions of the motor cortex, somatosensory cortex, and association areas? The cerebrum — the two cerebral hemispheres that contribute 85 percent of the brain’s weight — enables our perceiving, thinking, and speaking. Like other brain structures, including the thalamus, hippocampus, and amygdala, the cerebral hemispheres come as a pair. Covering those hemispheres, like bark on a tree, is the cerebral cortex, a thin surface layer of interconnected neural cells. (The scholars who first dissected and labeled the brain used Latin and Greek words as graphic descriptions. For example, cortex means “bark.”) cerebral [seh-REE-bruhl] cortex the intricate fabric of interconnected neural cells covering the forebrain’s cerebral hemispheres; the body’s ultimate control and information-processing center. Mammals’ complex cerebral cortex offers high capacity for learning and thinking, enabling them to adapt to ever-changing environments. What makes humans distinct is the size and interconnectivity of our cerebral cortex (Donahue et al., 2018). Let’s take a look at its structure and function. 404 Structure of the Cortex If you opened a human skull, exposing the brain, you would see a wrinkled organ, shaped somewhat like an oversized walnut. Without these wrinkles, a flattened cerebral cortex would require triple the area — roughly that of a large pizza. The brain’s left and right hemispheres are filled mainly with axons connecting the cortex to the brain’s other regions. The cerebral cortex — that thin surface layer — contains some 20 to 23 billion of the brain’s nerve cells and 300 trillion synaptic connections (de Courten-Myers, 2005). Being human takes a lot of nerve. Each hemisphere’s cortex is subdivided into four lobes, separated by prominent fissures, or folds (Figure 1.4-12). Starting at the front of your brain and moving over the top, there are the frontal lobes (behind your forehead), the parietal lobes (at the top and to the rear), and the occipital lobes (at the back of your head). Reversing direction and moving forward, just above your ears, you find the temporal lobes. Each of the four lobes carries out many functions, and many functions require the interplay of several lobes. frontal lobes the portion of the cerebral cortex lying just behind the forehead. They enable linguistic processing, muscle movements, higher-order thinking, and executive functioning (such as making plans and judgments). parietal [puh-RYE-uh-tuhl] lobes the portion of the cerebral cortex lying at the top of the head and toward the rear; it receives sensory input for touch and body position. occipital [ahk-SIP-uh-tuhl] lobes the portion of the cerebral cortex lying at the back of the head; it includes areas that receive information from the visual fields. 405 temporal lobes the portion of the cerebral cortex lying roughly above the ears; it includes the auditory areas, each of which receives information primarily from the opposite ear. They also enable language processing. Figure 1.4-12 The cortex and its basic subdivisions Functions of the Cortex More than a century ago, surgeons found damaged cortical areas during autopsies of people who had been partially paralyzed or speechless. This rather crude evidence did not prove that specific parts of the cortex control complex functions like movement or speech. A laptop with a broken power cord might go dead, but we 406 would be fooling ourselves if we thought we had “localized” the internet in the cord. Motor Functions Scientists had better luck in localizing simpler brain functions. For example, in 1870, German physicians Gustav Fritsch and Eduard Hitzig made an important discovery: Mild electrical stimulation to parts of an animal’s cortex made parts of its body move. The effects were selective: Stimulation caused movement only when applied to an arch-shaped region at the back of the frontal lobe, running roughly ear-to-ear across the top of the brain. Moreover, stimulating parts of this region in the left or right hemisphere caused movements of specific body parts on the opposite side of the body. Fritsch and Hitzig had discovered what is now called the motor cortex. motor cortex a cerebral cortex area at the rear of the frontal lobes that controls voluntary movements. Mapping the Motor Cortex Luckily for brain surgeons and their patients, the brain has no sensory receptors. Knowing this, in the 1930s, Otfrid Foerster and Wilder Penfield were able to map the motor cortex in hundreds of wide-awake patients by stimulating different cortical areas and observing the body’s responses. They discovered that body areas requiring precise control, such as the fingers and mouth, occupy the greatest amount of cortical space (Figure 1.4-13). In one of his many 407 demonstrations of motor behavior mechanics, Spanish neuroscientist José Delgado stimulated a spot on a patient’s left motor cortex, triggering the right hand to make a fist. Asked to keep the fingers open during the next stimulation, the patient, whose fingers closed despite his best efforts, remarked, “I guess, Doctor, that your electricity is stronger than my will” (Delgado, 1969, p. 114). Figure 1.4-13 Motor cortex and somatosensory cortex tissue devoted to each body part As you can see from this classic though inexact representation, the amount of cortex devoted to a body part in the motor cortex (in the frontal lobes) or in the somatosensory cortex (in the parietal lobes) is not proportional to that body part’s size. Rather, the brain devotes more tissue to sensitive areas and to areas requiring precise control. So, your fingers have a greater representation in the cortex than does your upper arm. Scientists can now predict a monkey’s arm motion just before it moves — by repeatedly measuring motor cortex activity preceding specific arm movements (Livi et al., 2019). Such findings have 408 opened the door to research on brain-controlled computer technology. Brain–Machine Interfaces Researchers wondered: By stimulating the brain, could we enable a person with paralysis to move a robotic limb? Could a brain– machine interface help someone with paralysis learn to command a cursor to write an email? To find out, researchers implanted 100 tiny recording electrodes in the motor cortexes of three monkeys (Nicolelis, 2011; Serruya et al., 2002). As the monkeys gained rewards by using a joystick to follow a moving red target, the researchers matched the brain signals with the arm movements. Then they programmed a computer to monitor the signals and operate the joystick. When a monkey merely thought about a move, the mind- reading computer moved the cursor with nearly the same proficiency as had the reward-seeking monkey. Monkey think, computer do. Clinical trials of such cognitive neural prosthetics have been under way with people who have severe paralysis or have lost a limb (Andersen et al., 2010; Rajangam et al., 2016). The first patient, a 25-year-old man with paralysis, was able to mentally control a TV, draw shapes on a computer screen, and play video games — all thanks to an aspirin-sized chip with 100 microelectrodes recording activity in his motor cortex (Hochberg et al., 2006). Other people with paralysis who have received implants have learned to direct robotic arms with their thoughts (Clausen et al., 2017). 409 And then there is Ian Burkhart, who lost the use of his arms and legs at age 19. Ohio State University brain researchers implanted recording electrodes in his motor cortex (Schwemmer et al., 2018). Imagine the process: Researchers instruct Burkhart to stare at a screen that shows a moving hand. Next, Burkhart imagines moving his own hand. Brain signals from his motor cortex feed into a computer, which gets the message that he wants to move his arm and thus stimulates those muscles. The result? Burkhart, with his very own paralyzed arm, grasps a bottle, dumps out its contents, and picks up a stick. He can even play the video game Guitar Hero. By learning Burkhart’s unique brain response patterns, the computer can predict his brain activity to help him make these movements. “It’s really restored a lot of the hope I have for the future to know that a device like this will be possible to use in everyday life,” Burkhart says, “for me and for many other people” (Wood, 2018). (See tinyurl.com/ControlMotorCortex.) If everything psychological is also biological — if, for example, every thought is also a neural event — could microelectrodes someday detect thoughts well enough to enable people to control their 410 environment with ever-greater precision (see Figure 1.4-14)? Scientists have even created a prosthetic voice, which creates (mostly) understandable speech by reading the brain’s motor commands that direct vocal movement (Anumanchipalli et al., 2019). Figure 1.4-14 Brain–machine interaction Electrodes planted in the hand area of the motor cortex, and in the hand, elbow, and shoulder muscles, helped a man with paralysis in all four limbs use his paralyzed arm to take a drink of coffee (Ajiboye et al., 2017). Such research advances are paving the way for restored movement in daily life, outside the controlled laboratory environment (Andersen, 2019; Andersen et al., 2010). Sensory Functions If the motor cortex sends messages out to the body, where does the cortex receive incoming messages? Penfield identified a cortical area — at the front of the parietal lobes, parallel to and just behind the motor cortex — that specializes in receiving information from the 411 skin senses, such as touch and temperature, and from the movement of body parts. We now call this area the somatosensory cortex. Stimulate a point on the top of this band of tissue and a person may report being touched on the shoulder; stimulate some point on the side and the person may feel something on the face. somatosensory cortex a cerebral cortex area at the front of the parietal lobes that registers and processes body touch and movement sensations. The more sensitive the body region, the larger the somatosensory cortex area devoted to it (see Figure 1.4-13). Your supersensitive lips project to a larger brain area than do your toes, which is one reason we kiss rather than touch toes. Rats have a large area of the brain devoted to their whisker sensations, and owls to their hearing sensations. Scientists have identified additional areas where the cortex receives input from senses other than touch. Any visual information you are receiving now is going to the visual cortex in your occipital lobes, at the back of your brain (Figures 1.4-15 and 1.4-16). If you have normal vision, you might see flashes of light or dashes of color if stimulated in your occipital lobes. (In a sense, we do have eyes in the back of our head!) Having lost much of his right occipital lobe in a tumor removal, a friend of mine [DM’s] was blind to the left half of his field of vision. Visual information travels from the occipital lobes to other areas that specialize in tasks such as identifying words, detecting emotions, and recognizing faces. 412 Figure 1.4-15 Seeing without eyes The psychoactive drug LSD often produces vivid hallucinations. Why? Because it dramatically increases communication between the visual cortex (in the occipital lobe) and other brain regions. These fMRI scans show (a) a research participant with closed eyes who has been given a placebo and (b) the same person under the influence of LSD. Color represents increased blood flow (Carhart-Harris et al., 2016). Other researchers have confirmed that LSD increases communication between brain regions (Preller et al., 2019; Timmermann et al., 2018). 413  Figure 1.4-16 The visual cortex and auditory cortex The visual cortex in the occipital lobes at the rear of your brain receives input from your eyes. The auditory cortex in your temporal lobes — above your ears — receives information from your ears. Any sound you now hear is processed by your auditory cortex in your temporal lobes ( just above your ears; see Figure 1.4-16). Most of this auditory information travels a circuitous route from one ear to the auditory receiving area above your opposite ear. If stimulated in your auditory cortex, you might hear a sound. When taken during the false sensory experience of auditory hallucinations, fMRI scans of people with schizophrenia reveal active auditory areas in the temporal lobes (Lennox et al., 1999). Even the phantom ringing 414 (“tinnitus”) sound experienced by people with hearing loss is — if heard in one ear — associated with activity in the temporal lobe on the brain’s opposite side (Muhlnickel, 1998). Association Areas So far, we have pointed out small cortical areas that either receive sensory input or direct muscular output. Together, these occupy about one-fourth of the human brain’s thin, wrinkled cover. What, then, goes on in the remaining vast regions of the cortex? In these association areas, neurons are busy with higher mental functions — many of the tasks that make us human. association areas areas of the cerebral cortex that are not involved in primary motor or sensory functions, but rather are involved in higher mental functions such as learning, remembering, thinking, and speaking. Electrically probing an association area won’t trigger any observable response. So, unlike the somatosensory and motor areas, association area functions cannot be neatly mapped. Does this mean we don’t use them — or that, as some 4 in 10 people agreed in two surveys, “We use only 10 percent of our brains” (Furnham, 2018; Macdonald et al., 2017)? (See the Developing Arguments feature: Do We Use Only 10 Percent of Our Brain?) AP® Science Practice Developing Arguments Do We Use Only 10 Percent of Our Brain? 415  Developing Arguments Questions 1. Using scientifically derived evidence, explain why the idea that we use only 10 percent of our brain is a myth. 2. Before reading the evidence presented here, were you under the impression that we use only around 10 percent of our brain? Identify the reasoning you found most compelling in refuting this myth. 1. McBurney, 1996, p. 44. Association areas are found in all four brain lobes. The prefrontal cortex in the forward part of the frontal lobes enables judgment, planning, social interactions, and processing of new memories. People with damage to this area may have high intelligence test scores and great cake-baking skills. Yet they would not be able to plan ahead to begin baking a cake for a birthday party (Huey et al., 2006). If they did begin to bake, they might forget the recipe (MacPherson et al., 2016). And if responsible for the absence of birthday cake, they may feel no regret (Bault et al., 2019). 416 Frontal lobe damage also can alter personality and remove a person’s inhibitions. Consider the classic case of railroad worker Phineas Gage. One afternoon in 1848, Gage, then 25 years old, was using a tamping iron to pack gunpowder into a rock. A spark ignited the gunpowder, shooting the rod up through his left cheek and out the top of his skull, leaving his frontal lobes damaged (Figure 1.4-17). To everyone’s amazement, Gage was immediately able to sit up and speak, and after the wound healed, he returned to work. But the blast damaged connections between his frontal lobes and the brain regions that control emotion and decision making (Thiebaut de Schotten et al., 2015; Van Horn et al., 2012). The previously friendly, soft-spoken man was now irritable, profane, and dishonest. This person, said his friends, was “no longer Gage.” Most of his mental abilities and memories were intact, but for the next few years his personality was not. (Gage later lost his railroad job, but over time he adapted to his disability and found work as a stagecoach driver [Macmillan & Lena, 2010].) 417 Figure 1.4-17 A blast from the past (a) Phineas Gage’s skull was kept as a medical record. Using measurements and modern neuroimaging techniques, researchers have reconstructed the probable path of the rod through Gage’s brain (Van Horn et al., 2012). (b) This photo shows Gage after his accident. (The image has been reversed to show the features correctly. Early photos, including this one, were actually mirror images.) AP® Science Practice Research Phineas Gage is a classic example of a case study, a non-experimental method. A case study hopes to reveal universal principles, but generalizing its findings requires further research. 418 Studies of other people with damaged frontal lobes have revealed similar impairments. Not only do they become less inhibited (without the frontal lobe brakes on their impulses), but their moral judgments also seem unrestrained. Cecil Clayton lost 20 percent of his left frontal lobe in a 1972 sawmill accident. Thereafter, his intelligence test score dropped to an elementary school level and he displayed increased impulsivity. In 1996, he fatally shot a deputy sheriff. In 2015, when he was 74, the State of Missouri executed him (Williams, 2015). The frontal lobes help steer us toward kindness and away from violence (Achterberg et al., 2020; Lieberman et al., 2019). With their frontal lobes ruptured, people’s moral compass seems separated from their actions. They know right from wrong but often don’t care. Association areas also perform other mental functions. The parietal lobes, parts of which were large and unusually shaped in Einstein’s normal-weight brain, enable mathematical and spatial reasoning (Amalric & Dehaene, 2019; Wilkey et al., 2018). Stimulation of one parietal lobe area in patients undergoing brain surgery produced a feeling of wanting to move an upper limb, the lips, or the tongue, but without any actual movement. With increased stimulation, patients falsely believed they had moved. Curiously, when surgeons stimulated a different association area near the motor cortex in the frontal lobes, the patients did move but had no awareness of doing so (Desmurget et al., 2009). These head-scratching findings suggest that our perception of moving flows not from the movement itself, but rather from our intention. 419 On the underside of the right temporal lobe, another association area enables us to instantly recognize faces (Retter et al., 2020). If a stroke or head injury destroyed this area of your brain, you would still be able to describe facial features and to recognize someone’s gender and approximate age, yet be strangely unable to identify the person as, say, Ariana Grande or even your grandmother. Nevertheless, complex mental functions don’t reside in any single place. During a complex task, a brain scan shows many islands of brain activity working together — some running automatically in the background, and others under conscious control (Chein & Schneider, 2012). Your memory, language, attention, and social skills result from functional connectivity — communication among distinct brain areas and neural networks (Bassett et al., 2018; Silston et al., 2018). What happens when brain areas struggle to communicate with each other? People are at increased risk for mental disorders (Baker et al., 2019; Zhang et al., 2019). The point to remember: Our mental experiences — and our psychological health — rely on coordinated brain activity. AP® Science Practice Check Your Understanding Examine the Concept Which part of the human brain distinguishes us most from other animals? Explain the differences among the brain’s four lobes in terms of their location and function. 420  Apply the Concept If you are able, try moving your right hand in a circular motion, as if cleaning a table. Then start your right foot doing the same motion, synchronized with your hand. Now reverse the right foot’s motion, but not the hand’s. Finally, try moving the left foot opposite to the right hand. a. Why is reversing the right foot’s motion so hard? b. Why is it easier to move the left foot opposite to the right hand? Explain why association areas are important using specific examples from your own experience. Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. Module 1.4b REVIEW 1.4-4 What are the hindbrain, midbrain, and forebrain? Vertebrate brains have three main divisions. The hindbrain contains brainstem structures that direct essential survival functions, such as breathing, sleeping, arousal, coordination, and balance. The midbrain connects the hindbrain with the forebrain; it controls some movement and transmits information that enables seeing and hearing. The forebrain manages complex cognitive activities, sensory and associative functions, and voluntary motor activities. 421 1.4-5 Which structures make up the brainstem, and what are the functions of the brainstem, thalamus, reticular formation, and cerebellum? The brainstem is responsible for automatic survival functions. Its components are the medulla (which controls heartbeat and breathing), the pons (which helps coordinate movements and control sleep), and the reticular formation (which filters incoming stimuli, relays information to other brain areas, and affects arousal). The thalamus, sitting above the brainstem, acts as the brain’s sensory control center. The cerebellum, attached to the rear of the brainstem, coordinates voluntary movement and balance and enables nonverbal learning and memory. 1.4-6 What are the limbic system’s structures and functions? The limbic system is linked to emotions, memory, and drives. Its neural centers include the amygdala (involved in behavior and emotional responses, such as aggression and fear), the hypothalamus (directs various bodily maintenance functions, helps govern the endocrine system, and is linked to emotion and reward), the hippocampus (helps process explicit, conscious memories), the thalamus, and the pituitary gland. The hypothalamus controls the pituitary by stimulating it to trigger the release of hormones. 422 1.4-7 What four lobes make up the cerebral cortex, and what are the functions of the motor cortex, somatosensory cortex, and association areas? The cerebral cortex has two hemispheres, and each hemisphere has four lobes: frontal, parietal, occipital, and temporal. Each lobe performs many functions and interacts with other areas of the cortex. The motor cortex, at the rear of the frontal lobes, controls voluntary movements. The somatosensory cortex, at the front of the parietal lobes, registers and processes body touch and movement sensations. Body parts requiring precise control (in the motor cortex) or those that are especially sensitive (in the somatosensory cortex) occupy the greatest amount of space. Most of the brain’s cortex — the major portion of each of the four lobes — is devoted to uncommitted association areas, which integrate information involved in higher mental functions such as learning, remembering, thinking, and speaking. Our mental experiences arise from coordinated brain activity. AP® Practice Multiple Choice Questions 1. Damage to which of the following puts a person’s life in the most danger because it may cause breathing to stop? 423  a. Amygdala b. Thalamus c. Medulla d. Hypothalamus 2. A gymnast falls and hits her head on the floor. She attempts to continue practicing but has trouble maintaining balance. What part of her brain has probably been affected? a. Reticular formation b. Cerebellum c. Amygdala d. Medulla 3. Stimulation of the amygdala is most likely to have which of the following effects? a. Happiness b. Aggression c. Hunger d. Loss of balance 4. Brennan feels hungry. Which brain area is most responsible for his hunger? 424  a. Amygdala b. Hypothalamus c. Hippocampus d. Brainstem 5. Damage to which of the following brain structures would affect the processing of new explicit memories? a. Cerebral cortex b. Medulla c. Hippocampus d. Hypothalamus 6. After being late to work for the fifth time, Hester declared, “My occipital lobes must not be working optimally! I have a hard time planning my day to be here on time!” If you were Hester’s boss, what might you say to her to modify her claim to make it more accurate? a. “Hester, it’s your frontal lobes that are not working optimally.” b. “Hester, it’s your temporal lobes that are not working optimally.” 425  c. “Hester, it’s your parietal lobes that are not working optimally.” d. “Hester, it’s your somatosensory cortex that is not working optimally.” 7. Stimulation of which of the following may cause a person to involuntarily move their arm? a. Somatosensory cortex b. Motor cortex c. Glial cells d. Visual cortex 8. Which lobe of the brain is the arrow pointing to? a. Occipital 426 b. Parietal c. Frontal d. Temporal 427 Module 1.4c The Brain: Damage Response and Brain Hemispheres Learning Targets 1.4-8 Explain how a damaged brain can reorganize itself, and describe neurogenesis. 1.4-9 Explain what split brains reveal about the functions of our two brain hemispheres. Responses to Damage 1.4-8 To what extent can a damaged brain reorganize itself, and what is neurogenesis? Earlier, we learned about neuroplasticity — how our brain adapts to new situations. What happens when we experience mishaps, large and small? Let’s explore the brain’s ability to modify itself after damage. Most brain-damage effects described earlier can be traced to two hard facts: (1) Severed brain and spinal cord neurons, unlike cut skin, usually do not regenerate. (If your spinal cord were severed, you would probably be permanently paralyzed.) And (2) some brain functions seem preassigned to specific areas. One newborn who suffered damage to a temporal lobe area responsible for facial recognition was never able to recognize faces (Farah et al., 2000). But 428 there is good news: Some neural tissue can reorganize in response to damage. Neuroplasticity may also occur after serious damage, especially in young children whose undamaged hemisphere develops extra connections (Lindenberger & Lövdén, 2019; see also Figure 1.4-18). The brain’s plasticity is good news for those with vision or hearing loss. Blindness or deafness makes unused brain areas available for other uses, such as sound and smell (Amedi et al., 2005; Bauer et al., 2017). If a blind person uses one finger to read Braille, the brain area dedicated to that finger expands as the sense of touch invades the visual cortex that normally helps people see (Barinaga, 1992; Sadato et al., 1996). In sighted people, Braille-reading training produces similar brain changes (Debowska et al., 2016). Figure 1.4-18 Brain work is child’s play 429  This 6-year-old child had surgery to end her life-threatening seizures. Although most of her right hemisphere was removed (see the MRI of a similar hemispherectomy), her remaining hemisphere compensated by putting other areas to work. Reflecting on their child hemispherectomies, one Johns Hopkins team reported being “awed” by how well the children had retained their memory, personality, and humor (Vining et al., 1997). The younger the child, the greater the chance that the remaining hemisphere can take over the functions of the one that was surgically removed. Neuroplasticity also helps explain why some studies have found that deaf people who learned sign language before another language may have enhanced peripheral and motion-detection vision (Brooks et al., 2020). In deaf people whose native language is sign, the temporal lobe area dedicated to hearing waits in vain for stimulation. Finally, it looks for other signals to process, such as those from the visual system used to see and interpret signs. Similar reassignment may occur when disease or damage frees up other brain areas normally dedicated to specific functions. If a slow- growing left hemisphere tumor disrupts language (which resides mostly in the left hemisphere), the right hemisphere may compensate (Thiel et al., 2006). If a finger is amputated, the somatosensory cortex that received its input will begin to receive input from the adjacent fingers, which then become more sensitive (Oelschläger et al., 2014). Although the brain often attempts self-repair by reorganizing existing tissue, researchers are debating whether it can also mend itself through neurogenesis — producing new neurons (Kempermann et al., 2018). Researchers have found baby neurons 430 deep in the brains of adult mice, birds, monkeys, and humans (He & Jin, 2016; Jessberger et al., 2008). These neurons may then form connections with neighboring neurons (Gould, 2007; Luna et al., 2019). neurogenesis the formation of new neurons. Stem cells, which can develop into any type of brain cell, have also been discovered in the human embryo. If mass-produced in a lab and injected into a damaged brain, might neural stem cells turn themselves into replacements for lost brain cells? Might surgeons someday be able to rebuild damaged brains, much as we reseed the grass on damaged sports fields? Stay tuned. In the meantime, we can all benefit from natural promoters of neurogenesis, such as exercise, sleep, and nonstressful but stimulating environments (Liu & Nusslock, 2018; Monteiro et al., 2014; Nollet et al., 2019). The Divided Brain 1.4-9 What do split brains reveal about the functions of our two brain hemispheres? Our brain’s look-alike left and right hemispheres serve differing functions. This lateralization becomes apparent after brain damage. Research spanning more than a century has shown that left- hemisphere accidents, strokes, and tumors can impair reading, writing, speaking, arithmetic reasoning, and understanding. Similar 431 right-hemisphere damage has less visibly dramatic effects. Does this mean that the right hemisphere is just along for the ride? Many believed this was the case until the 1960s, when a fascinating chapter in psychology’s history began to unfold: Researchers found that the “minor” right hemisphere was not so limited after all. Splitting the Brain In the early 1960s, two neurosurgeons speculated that major epileptic seizures were caused by an amplification of abnormal brain activity bouncing back and forth between the two cerebral hemispheres, which work together as an integrated system (Bogen & Vogel, 1962). They wondered if they could end this biological tennis match by severing the corpus callosum, the wide band of axon fibers connecting the two hemispheres and carrying messages between them (Figure 1.4-19). The neurosurgeons knew that psychologists Roger Sperry, Ronald Myers, and Michael Gazzaniga had divided cats’ and monkeys’ brains in this manner, with no serious ill effects. corpus callosum [KOR-pus kah-LOW-sum] the large band of neural fibers connecting the two brain hemispheres and carrying messages between them. 432  Figure 1.4-19 The corpus callosum This large band of neural fibers connects the two brain hemispheres. (a) To photograph this half-brain, a surgeon separated the hemispheres by cutting through the corpus callosum (see the blue arrow) and lower brain regions. (b) This high- resolution diffusion spectrum image, showing a top-facing brain from above, reveals the brain neural networks within the two hemispheres, and the corpus callosum neural bridge between them. So, the surgeons operated. The result? The seizures all but disappeared. The patients with these split brains were surprisingly healthy, with their personality and intellect hardly affected. Waking from surgery, one even joked that he had a “splitting headache” (Gazzaniga, 1967). By sharing their experiences, these patients have greatly expanded our understanding of interactions between the intact brain’s two hemispheres. split brain a condition resulting from surgery that separates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them. To appreciate these findings, we need to focus for a minute on the peculiar nature of our visual wiring, illustrated in Figure 1.4-20. 433 Note that each eye receives sensory information from the entire visual field. But in each eye, information from the left half of your field of vision goes to your right hemisphere, and information from the right half of your visual field goes to your left hemisphere, which usually controls speech. Information received by either hemisphere is quickly transmitted to the other across the corpus callosum. In a person with a severed corpus callosum, this information sharing does not take place. 434 Figure 1.4-20 The information highway from eye to brain 435 Knowing these facts, Sperry and Gazzaniga could send information to a patient’s left or right hemisphere. As the person stared at a spot, the researchers flashed a stimulus to its right or left. They could do this with you, too, but in your intact brain, the hemisphere receiving the information would instantly pass the news to the other side. Because the split-brain surgery had cut the communication lines between the hemispheres, the researchers could, with these patients, quiz each hemisphere separately. In an early experiment, Gazzaniga (1967) asked split-brain patients to stare at a dot as he flashed HE ART on a screen (Figure 1.4-21). Thus, HE appeared in their left visual field (which transmits to the right hemisphere) and ART in the right field (which transmits to the left hemisphere). When he then asked them to say what they had seen, the patients reported that they had seen ART. But when asked to point with their left hand to what they had seen, they were startled when their hand (controlled by the right hemisphere) pointed to HE. Given an opportunity to express itself, each hemisphere indicated what it had seen. The right hemisphere (controlling the left hand) intuitively knew what it could not verbally report. 436  Figure 1.4-21 One skull, two minds When an experimenter flashes HE ART across the visual field, a woman with a split brain verbally reports seeing the word transmitted to her left hemisphere. However, if asked to indicate with her left hand what she saw, she points to the word transmitted to her right hemisphere (Gazzaniga, 1983). When a picture of a spoon was flashed to their right hemisphere, the patients could not say what they had viewed. But when asked to identify what they had viewed by feeling an assortment of hidden objects with their left hand, they readily selected the spoon. If the experimenter said, “Correct!” the patient might reply, “What? Correct? How could I possibly pick out the correct object when I don’t know what I saw?” It is, of course, the left hemisphere doing the talking here, bewildered by what the nonverbal right hemisphere knows. 437 A few people who have undergone split-brain surgery have been for a time bothered by the unruly independence of their left hand. It was as if the left hand truly didn’t know what the right hand was doing. The left hand might unbutton a shirt while the right hand buttoned it, or put grocery store items back on the shelf after the right hand put them in the cart. It was as if each hemisphere was thinking, “I’ve half a mind to wear my green (blue) shirt today.” Indeed, said Sperry (1964), split-brain surgery leaves people “with two separate minds.” With a split brain, both hemispheres can comprehend and follow an instruction to copy — simultaneously — different figures with the left and right hands (Franz et al., 2000; see also Figure 1.4-22). Today’s researchers believe that a split-brain patient’s mind resembles a river that has branched into separate streams, each unaware of its influence on the other (Pinto et al., 2017). (Reading these reports, can you imagine a patient enjoying a solitary game of “rock, paper, scissors” — left versus right hand?) Figure 1.4-22 Try this! People who have had split-brain surgery can simultaneously draw two different shapes. 438 When the “two minds” are at odds, the left hemisphere does mental gymnastics to rationalize reactions it does not understand. If a patient follows an order (“Walk”) sent to the right hemisphere, a strange thing happens. The left hemisphere, unaware of the order, doesn’t know why the patient begins walking. But if asked, the patient doesn’t reply, “I don’t know.” Instead, the left hemisphere improvises — “I’m going into the house to get a Coke.” Gazzaniga (2006), who described these patients as “the most fascinating people on earth,” realized that the conscious left hemisphere resembles an “interpreter” that instantly constructs explanations. The brain, he concluded, often runs on autopilot; it acts first and then explains itself. AP® Science Practice Check Your Understanding Examine the Concept Explain what is meant by split brain. Explain the classic split-brain studies. Apply the Concept (a) If we flash a red light to the right hemisphere of a person with a split brain, and flash a green light to the left hemisphere, will each hemisphere observe its own color? (b) Will the person be aware that the colors differ? (c) What will the person verbally report seeing? Can you put yourself in the shoes of a patient with a split brain? What would it be like to have knowledge which you were unaware of and couldn’t verbally report but were nevertheless able to act on? Answers to the Examine the Concept questions can be found in Appendix C at the end of the book. 439 Right–Left Differences in the Intact Brain So, what about the 99.99+ percent of us with undivided brains? Does each of our hemispheres also perform distinct functions? The short answer is Yes. When a person performs a perceptual task, a brain scan often reveals increased activity (brain waves, blood flow, and glucose consumption) in the right hemisphere. When the person speaks or does a math calculation, activity usually increases in the left hemisphere. A dramatic demonstration of hemispheric specialization happens before some types of brain surgery. To locate the patient’s language centers, the surgeon injects a sedative into the neck artery feeding blood to the left hemisphere, which usually controls speech. Before the injection, the patient is lying down, arms in the air, chatting with the doctor. Can you predict what happens when the drug puts the left hemisphere to sleep? Within seconds, the person’s right arm falls limp. If the left hemisphere is controlling language, the patient will be speechless until the drug wears off. If the drug is injected into the artery to the right hemisphere, the left arm will fall limp, but the person will still be able to speak. To the brain, language is language, whether spoken or signed. (See Module 3.5 for more on how and where the brain processes language.) Just as hearing people usually use the left hemisphere to process spoken language, deaf people use the left hemisphere to 440 process sign language (Corina et al., 1992; Hickok et al., 2001). Thus, a left hemisphere stroke disrupts a deaf person’s signing, much as it would disrupt a hearing person’s speaking (Corina, 1998). Although the left hemisphere is skilled at making quick, literal interpretations of language, the right hemisphere excels at making inferences (Beeman & Chiarello, 1998; Bowden & Beeman, 1998; Mason & Just, 2004). When given an insight-like problem — “Which word goes with boot, summer, and ground?” — the right hemisphere more quickly comes to a reasoned conclusion and recognizes the solution: camp. As one patient explained after a right hemisphere stroke, “I understand words, but I’m missing the subtleties.” helps us modulate our speech to make meaning clear — as when we say, “Let’s eat, Grandpa!” instead of “Let’s eat Grandpa!” (Heller, 1990). helps orchestrate our self-awareness. People who suffer partial paralysis will sometimes stubbornly deny their impairment — constantly claiming they can move a paralyzed limb — if the damage occurs to the right hemisphere (Berti et al., 2005). Simply looking at the two hemispheres, so alike to the naked eye, who would suppose they each contribute uniquely to the harmony of the whole? Yet a variety of observations — of people with split brains, of people with healthy brains, and even of other species’ brains — converge beautifully, leaving little doubt that we have unified brains 441 with specialized parts (Hopkins & Cantalupo, 2008; MacNeilage et al., 2009). AP® Exam Tip Notice that your authors never refer to your left brain or your right brain. You have two brain hemispheres, each with its own responsibilities, but you have only one brain. It’s very misleading when the popular press refers to the left brain and the right brain. When studying for the AP® exam, avoid psychology myths. Module 1.4c REVIEW 1.4-8 To what extent can a damaged brain reorganize itself, and what is neurogenesis? While brain and spinal cord neurons usually do not regenerate, some neural tissue can reorganize in response to damage. The damaged brain may demonstrate neuroplasticity, especially in young children, as new pathways are built and functions migrate to other brain regions. Reassignment of functions to different areas of the brain may also occur in blindness and deafness, or as a result of damage and disease. Some research suggests that the brain may sometimes mend itself by forming new neurons, a process known as neurogenesis. 442 1.4-9 What do split brains reveal about the functions of our two brain hemispheres? Split-brain research (experiments on people with a severed corpus callosum) has confirmed that in most people, the left hemisphere is the more verbal. The right hemisphere excels in visual perception and making inferences, and helps us modulate our speech and orchestrate our self-awareness. Studies of the intact brain in healthy people confirm that each hemisphere makes unique contributions to the integrated functioning of the whole brain. AP® Practice Multiple Choice Questions 1. Nan was in a car accident, which resulted in brain damage. However, some of her brain areas took over the function of the damaged area, thanks to the role of a. lesioning. b. positron emission training. c. neuroplasticity. d. the split brain. 2. Dr. Cantor studies neurogenesis, to understand how 443  a. one brain structure takes on the functions of an adjacent structure. b. the brain creates new neurons. c. association areas expand as new material is learned. d. the brain adapts to new learning. Use the following text to answer questions 3 and 4: A patient who has undergone split-brain surgery has a picture of a dog flashed to his right hemisphere and a cat to his left hemisphere. 3. In this example, the patient will be able to identify the a. cat using his right hand. b. dog using his right hand. c. dog using either hand. d. cat using his left hand. 4. In this example, which of the following will the patient