AP Psychology Placement Test Pre-Reading 2024 PDF

Older Brain Structures 11-2 What structures make up the brainstem, and what are the functions of the brainstem, thalamus, reticular formation, and cerebellum? An animal’s capacities come from its brain structures. In primitive animals, such as sharks, a not-so-complex brain primar...

Older Brain Structures 11-2 What structures make up the brainstem, and what are the functions of the brainstem, thalamus, reticular formation, and cerebellum? An animal’s capacities come from its brain structures. In primitive animals, such as sharks, a not-so-complex brain primarily regulates basic survival functions: breathing, resting, and feeding. In lower mammals, such as rodents, a more complex brain enables emotion and greater memory. In advanced mammals, such as humans, a brain that processes more information enables increased foresight as well. AP® EXAM TIP Your authors, David Myers and Nathan DeWall, 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 brain’s increasing complexity arises from new systems built on top of the old, much as Earth’s landscape covers the old with the new. Digging down, one discovers the fossil remnants of the past—brainstem components performing for us much as they did for our distant ancestors. Let’s start with the brain’s base and work up to the newer systems. The Brainstem The brainstem is the brain’s oldest and innermost region. Its base is the medulla, the slight swelling in the spinal cord just after it enters the skull (Figure 11.4). Here lie the controls for your heartbeat and breathing. As some brain-damaged patients in a vegetative state illustrate, we need no higher brain or conscious mind to orchestrate our heart’s pumping and 319 lungs’ breathing. The brainstem handles those tasks. Just above the medulla sits the pons, which helps coordinate movements and control sleep. brainstem the oldest part and 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 base of the brainstem; controls heartbeat and breathing. Figure 11.4 The brainstem and thalamus 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. If a cat’s brainstem is severed from the rest of the brain above it, the animal will still breathe and live—and even run, climb, and groom (Klemm, 1990). But cut off from the brain’s higher regions, it won’t purposefully run or climb to get food. 320  The brainstem is a crossover point, where most nerves to and from each side of the brain connect with the body’s opposite side (Figure 11.5). This peculiar cross-wiring is but one of the brain’s many surprises. Figure 11.5 The body’s wiring Nerves from the left side of the brain are mostly linked to the right side of the body, and vice versa. The Thalamus Sitting atop the brainstem is the thalamus, a pair of egg-shaped structures that act as the brain’s sensory control center (Figure 11.5). The thalamus receives information from all the senses except smell, and routes that information to the higher brain regions that deal with seeing, hearing, tasting, and touching. The thalamus also receives some of the higher brain’s replies, which it then directs to the medulla and to the cerebellum (see below). For sensory information, your thalamus is something like London’s Heathrow Airport, a hub through which traffic flows in and out on its way to various locations. 321  thalamus [THAL-uh-muss] the brain’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, a neuron network extending 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. Have you multitasked today? You can thank your reticular formation (Wimmer et al., 2015). reticular formation a nerve network that travels through the brainstem into the thalamus and plays an important role in controlling arousal. The reticular formation also controls arousal, as Giuseppe Moruzzi and Horace Magoun discovered in 1949. Electrically stimulating a sleeping cat’s reticular formation 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 baseball-sized cerebellum, meaning “little brain,” which is what its two wrinkled halves resemble (Figure 11.6). As you will see in Module 32, the cerebellum enables nonverbal learning and skill memory. It also helps us judge time, modulate our emotions, and discriminate sounds and textures (Bower & Parsons, 322 2003). And (with assistance from the pons) it coordinates voluntary movement. When a soccer player masterfully controls the ball, give the player’s cerebellum some credit. Under alcohol’s influence on the cerebellum, coordination suffers. And if you injured your cerebellum, you would have difficulty walking, keeping your balance, or shaking hands. Your movements would be jerky and exaggerated. Gone would be any dreams of being a dancer or guitarist. cerebellum [sehr-uh-BELL-um] the “little brain” at the rear of the brainstem; functions include processing sensory input, coordinating movement output and balance, and enabling nonverbal learning and memory. Figure 11.6 The brain’s organ of agility Hanging at the back of the brain, the cerebellum coordinates our voluntary movements, as when soccer star Cristiano Ronaldo controls the ball. *** Note: These older brain functions all occur without any conscious effort. This illustrates another of our recurring themes: Our brain processes most 323 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. Likewise, whether we are asleep or awake, our brainstem manages its life-sustaining functions, freeing our newer brain regions to think, talk, dream, or savor a memory. Check Your Understanding Ask Yourself Are you surprised to learn about all the information-processing that happens automatically, without your knowledge? Why or why not? Test Yourself 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. Answers to the Test Yourself questions can be found in Appendix E at the end of the book. 324 The Limbic System 11-3 What are the limbic system’s structures and functions? We’ve considered the brain’s oldest parts, but we’ve not yet reached its newest and highest regions, the cerebral hemispheres (the two halves of the brain). Between the oldest and newest brain areas lies the limbic system (limbus means “border”). This system contains the amygdala, the hypothalamus, and the hippocampus (Figure 11.7). limbic system neural system (including the amygdala, hypothalamus, and hippocampus) located below the cerebral hemispheres; associated with emotions and drives. Figure 11.7 The limbic system This neural system sits between the brain’s older parts and its cerebral hemispheres. The limbic system’s hypothalamus controls the nearby pituitary gland. Flip It Video: Limbic System The Amygdala Research has linked the amygdala, two lima-bean-sized neural clusters, to 325 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 most mellow of creatures. In studies with other wild animals, including the lynx, wolverine, and wild rat, researchers noted the same effect. So, too, with human patients. Those with amygdala lesions often display reduced arousal to fear- and anger-arousing stimuli (Berntson et al., 2011). One such woman, 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. Aggression as a brain state Back arched and fur fluffed, this fierce cat is ready to attack. Electrical stimulation of a cat’s amygdala provokes angry reactions, suggesting the amygdala’s role in aggression. Which ANS division is activated by such stimulation?1 These and other experiments have confirmed the amygdala’s role in emotions such as fear and rage. One study found math anxiety associated 326 with hyperactivity in the right amygdala (Young et al., 2012). Monkeys and humans with amygdala damage become less fearful of strangers (Harrison et al., 2015). Other studies link criminal behavior with amygdala dysfunction (Boccardi et al., 2011; Ermer et al., 2012). When people view angry and happy faces, only the angry ones increase activity in the amygdala (Mende-Siedlecki et al., 2013). But we must be careful. The brain is not neatly organized into structures that correspond to our behavior categories. When we feel afraid or act aggressively, there is neural activity in many areas of our brain—not just the amygdala. If you destroy a car’s battery, it’s true that you won’t be able to start the engine. But the battery is merely one link in an integrated system. The Hypothalamus Just below (hypo) the thalamus is the hypothalamus (Figure 11.8), 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 neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system via the pituitary gland, and is linked to emotion and reward. 327  Figure 11.8 The hypothalamus This small but important structure, colored yellow/orange in this MRI scan, helps keep 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, picking 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 adjacent “master gland” of the endocrine system, your pituitary (see Figure 11.7), to influence your sex glands to release their hormones. These hormones will intensify the thoughts of sex in your cerebral cortex. (Once again, we see 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). Curiously, as if seeking more stimulation, the rat kept returning to the location where it had been stimulated by this misplaced electrode. On 328 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 (Olds, 1975). 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, not “pleasure centers.”) Just how rewarding are these reward centers? Enough to cause rats to self-stimulate these brain regions more than 1000 times per hour. Moreover, they would even cross an electrified floor that a starving rat would not cross to reach food (Figure 11.9). Figure 11.9 Rat with an implanted electrode With an electrode implanted in a reward center of its hypothalamus, the rat readily crosses an electrified grid, accepting the painful shocks, to press a pedal that sends electrical impulses to that center. 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. Researchers are experimenting with new ways of using brain stimulation to control nonhuman animals’ actions in search-and-rescue operations. By rewarding rats for turning left or right, one research team 329 trained previously caged rats to navigate natural environments (Talwar et al., 2002; Figure 11.10). By pressing buttons on a laptop, the researchers were then able to direct the rat—which carried a receiver, power source, and video camera all in a tiny backpack—to turn on cue, climb trees, scurry along branches, and return. Figure 11.10 Ratbot on a pleasure cruise When stimulated by remote control, a rat could be guided to navigate across a field and even up a tree. Do humans have limbic centers for pleasure? To calm violent patients, one neurosurgeon implanted electrodes in such areas. Stimulated patients reported mild pleasure; unlike Olds’ rats, however, they were not driven to a frenzy (Deutsch, 1972; Hooper & Teresi, 1986). Moreover, newer research reveals that stimulating the brain’s “hedonic hotspots” (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, dopamine release produces our pleasurable “chills” response to a favorite piece of music (Zatorre & Salimpoor, 2013). “ 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. ” 330  Candace Pert (1986) Some researchers believe that substance use disorders may stem from malfunctions in 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 (Blum et al., 1996). The Hippocampus The hippocampus—a seahorse-shaped brain structure—processes conscious, explicit memories and decreases in size and function as we grow older. 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 players who experience one or more loss-of-consciousness concussions may later have a shrunken hippocampus and poor memory (Strain et al., 2015). Module 54 offers additional detail about how hippocampus size and function decrease as we grow older. Module 32 explains how our two-track mind uses the hippocampus to process our memories. hippocampus a neural center located in the limbic system; helps process for storage explicit (conscious) memories of facts and events. *** Figure 11.11 locates the brain areas we’ve discussed, as well as the cerebral cortex, our next topic. 331  Figure 11.11 Brain structures and their functions Check Your Understanding Ask Yourself If one day researchers discover how to stimulate human limbic centers to produce as strong a reaction as found in other animals, do you think this process could be used to reduce the incidence of substance use? Could such use have any negative consequences? Test Yourself What are the three key structures of the limbic system, and what functions do they serve? Electrical stimulation of a cat’s amygdala provokes angry reactions. Which autonomic nervous system division is activated by such stimulation? In what brain region would damage be most likely to (1) disrupt your ability to jump rope? (2) disrupt your ability to hear? (3) leave you in a coma? (4) cut off the very breath and heartbeat of life? Answers to the Test Yourself questions can be found in Appendix E at the end of the book. 332