Chapter 2: Cognitive Neuroscience PDF

COVID-19 has exposed the brain's complex vulnerability, impacting it via two different pathways. The virus can directly cause diseases like encephalitis and delirium, but it can also cause extreme stress, which has a negative impact on mental health and highlights the close connection between mental...

COVID-19 has exposed the brain's complex vulnerability, impacting it via two different pathways. The virus can directly cause diseases like encephalitis and delirium, but it can also cause extreme stress, which has a negative impact on mental health and highlights the close connection between mental and physical stressors and brain function. The stress response begins in the brain where the amygdala sends a distress signal to the hypothalamus which in turn functions like the command center communicating with the rest of the body through the nervous system triggering a flight, fight, or fear response. CHAPTER 2: COGNITIVE NEUROSCIENCE Our brains are a central processing unit for everything we do. Cognitive psychologists are especially concerned with how the anatomy (physical structures of the body) and the physiology (functions and processes of the body) of the nervous system affect and are affected by human cognition. Cognitive neuroscience is the field of study linking the brain and other aspects of the nervous system to cognitive processing and, ultimately, to behavior. The brain is the organ in our bodies that most directly controls our thoughts, emotions, and motivations. We usually think of the brain as being at the top of the body’s hierarchy—as the boss, with various other organs responding to it. Like any good boss, however, it listens to and is influenced by its subordinates, the other organs of the body. Thus, the brain is reactive as well as directive. A major goal of present research on the brain is to study localization of function. Localization of function refers to the specific areas of the brain that control specific skills or behaviors. Cognition in the Brain: The Anatomy and Mechanisms of the Brain The nervous system is the basis for our ability to perceive, adapt to, and interact with the world around us (Gazzaniga, 1995, 2000; Gazzaniga, Ivry, & Mangun, 1998). Through this system we receive, process, and then respond to information from the environment (Pinker, 1997a; Rugg, 1997). In the following section, we will focus on the supreme organ of the nervous system—the brain—paying special attention to the cerebral cortex, which controls many of our thought processes. In a later section, we consider the basic building block of the nervous system—the neuron. The nervous system has two main parts: The central nervous system is made up of the brain and spinal cord. The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body. The nervous system transmits signals between the brain and the rest of the body, including internal organs. In this way, the nervous system’s activity controls the ability to move, breathe, see, think, and more. Gross Anatomy of the Brain: Forebrain, Midbrain, Hindbrain What have scientists discovered about the human brain? The brain has three major regions: forebrain, midbrain, and hindbrain. These labels do not correspond exactly to locations of regions in an adult or even a child’s head. Rather, the terms come from the front-to-back physical arrangement of these parts in the nervous system of a developing embryo. Initially, the forebrain is generally the farthest forward, toward what becomes the face. The midbrain is next in line. And the hindbrain is generally farthest from the forebrain, near the back of the neck. The Forebrain The forebrain is the region of the brain located toward the top and front of the brain. It comprises the cerebral cortex, the basal ganglia, the limbic system, the thalamus, and the hypothalamus. The Forebrain The forebrain, the most prominent part of the mammalian brain, consists of two cerebral hemispheres, one on the left and one on the right. Each hemisphere is organized to receive sensory information, mostly from the contralateral (opposite) side of the body. It controls muscles, mostly on the contralateral side. The Forebrain The cerebral cortex is the outer layer of the cerebral hemispheres. It plays a vital role in our thinking and other mental processes. The Forebrain The outer portion is the cerebral cortex. (Cerebrum is a Latin word for “brain.” Cortex is a Latin word for “bark” or “shell.”) Under the cerebral cortex are other structures, including the thalamus and the basal ganglia. The Forebrain The basal ganglia (singular: ganglion) are collections of neurons crucial to motor function. Dysfunction of the basal ganglia can result in motor deficits. These deficits include tremors, involuntary movements, changes in posture and muscle tone, and slowness of movement. Deficits are observed in Parkinson’s disease and Huntington’s disease. Both these diseases entail severe motor symptoms (Rockland, 2000; Lerner & Riley, 2008; Lewis & Barker, 2009). The Forebrain The limbic system is important to emotion, motivation, memory, and learning. Our limbic system allows us to suppress instinctive responses (e.g., the impulse to strike someone who accidentally causes us pain). Our limbic systems help us to adapt our behaviors flexibly in response to our changing environment. The limbic system comprises three central interconnected cerebral structures: the septum, the amygdala, and the hippocampus. The Forebrain The limbic system is the part of the brain involved in our behavioural and emotional responses, especially when it comes to behaviours we need for survival: feeding, reproduction and caring for our young, and fight or flight responses. The Forebrain The septum is involved in anger and fear. The amygdala plays an important role in emotion as well, especially in anger and aggression (Adolphs, 2003; Derntl et al., 2009). Stimulation of the amygdala commonly results in fear. It can be evidenced in various ways, such as through palpitations, fearful hallucinations, or frightening flashbacks in memory (Engin & Treit, 2008; Gloor, 1997; Rockland, 2000). The Forebrain Damage to (lesions in) or removal of the amygdala can result in maladaptive lack of fear. The amygdala also has an enhancing effect for the perception of emotional stimuli. In humans, lesions to the amygdala prevent this enhancement (Anderson & Phelps, 2001; Tottenham, Hare, & Casey, 2009). Additionally, persons with autism display limited activation in the amygdala. A well-known theory of autism suggests that the disorder involves dysfunction of the amygdala, which leads to the social impairment that is typical of persons with autism, for example, difficulties in evaluating people’s trustworthiness or recognizing emotions in faces (Adolphs, Sears, & Piven, 2001; Baron-Cohen et al., 2000; Howard et al., 2000; Kleinhans et al., 2009) The Forebrain The hippocampus plays an essential role in memory formation (Eichenbaum, 1999, 2002; Gluck, 1996; Manns & Eichenbaum, 2006; O’Keefe, 2003). The hippocampus is essential for flexible learning and for seeing the relations among items learned as well as for spatial memory (Eichenbaum, 1997; Squire, 1992). The hippocampus also appears to keep track of where things are and how these things are spatially related to each other. In other words, it monitors what is where (Cain, Boon, & Corcoran, 2006; Howland et al., 2008; McClelland et al., 1995; Tulving & Schacter, 1994). The Forebrain People who have suffered damage to or removal of the hippocampus still can recall existing memories— for example, they can recognize old friends and places— but they are unable to form new memories (relative to the time of the brain damage). New information—new situations, people, and places— remain forever new. A disease that produces loss of memory function is Korsakoff’s syndrome. The Forebrain This loss is believed to be associated with deterioration of the hippocampus and is caused by a lack of thiamine (Vitamin B-1) in the brain. The syndrome can result from excessive alcohol use, dietary deficiencies, or eating disorders. The Forebrain The thalamus relays incoming sensory information through groups of neurons that project to the appropriate region in the cortex. The thalamus also helps in the control of sleep and waking. When the thalamus malfunctions, the result can be pain, tremor, amnesia, impairment of language, and disruptions in waking and sleeping (Rockland, 2000; Steriade, Jones, & McCormick, 1997). The Forebrain The hypothalamus regulates behavior related to species survival: fighting, feeding, fleeing, and mating. The hypothalamus also is active in regulating emotions and reactions to stress (Malsbury, 2003). It interacts with the limbic system. The Forebrain The hypothalamus plays a role in sleep: Dysfunction and neural loss within the hypothalamus are noted in cases of narcolepsy, whereby a person falls asleep often and at unpredictable times (Lodi et al., 2004; Mignot, Taheri, & Nishino, 2002). The Forebrain The hypothalamus also is important for the functioning of the endocrine system. It is involved in the stimulation of the pituitary glands, through which a range of hormones are produced and released. These hormones include growth hormones and oxytocin (which is involved in bonding processes and sexual arousal; Gazzaniga, Ivry, & Mangun, 2009). The Forebrain Damage to any hypothalamic nucleus leads to abnormalities in motivated behaviors, such as feeding, drinking, temperature regulation, sexual behavior, fighting, or activity level. The Forebrain The pituitary gland is an endocrine (hormone- producing) gland attached to the base of the hypothalamus. In response to messages from the hypothalamus, the pituitary synthesizes hormones that the blood carries to organs throughout the body. The Midbrain The midbrain helps to control eye movement and coordination. The midbrain is more important in nonmammals where it is the main source of control for visual and auditory information. In mammals these functions are dominated by the forebrain. The Midbrain Superior colliculi (on top) Involved in vision (especially visual reflexes). Inferior colliculi (below) Involved in hearing. The Midbrain By far the most indispensable of these structures is the reticular activating system (RAS; also called the “reticular formation”), a network of neurons essential to the regulation of consciousness (sleep; wakefulness; arousal; attention to some extent; and vital functions such as heartbeat and breathing; Sarter, Bruno, & Berntson, 2003). The RAS also extends into the hindbrain. Both the RAS and the thalamus are essential to our having any conscious awareness of or control over our existence. The Midbrain The brainstem connects the forebrain to the spinal cord. It comprises the hypothalamus, the thalamus, the midbrain, and the hindbrain. A structure called the periaqueductal gray (PAG) is in the brainstem. This region seems to be essential for certain kinds of adaptive behaviors. Injections of small amounts of excitatory amino acids or, alternatively, electrical stimulation of this area results in any of several responses: an aggressive, confrontational response; avoidance or flight response; heightened defensive reactivity; or reduced reactivity as is experienced after a defeat, when one feels hopeless (Bandler & Shipley, 1994; Rockland, 2000). The Midbrain Physicians make a determination of brain death based on the function of the brainstem. Specifically, a physician must determine that the brainstem has been damaged so severely that various reflexes of the head (e.g., the pupillary reflex) are absent for more than 12 hours, or the brain must show no electrical activity or cerebral circulation of blood (Berkow, 1992). The Hindbrain The medulla oblongata controls heart activity and largely controls breathing, swallowing, and digestion. The Hindbrain The pons serves as a kind of relay station because it contains neural fibers that pass signals from one part of the brain to another. Its name derives from the Latin for “bridge,” as it serves a bridging function. The Hindbrain The cerebellum (from Latin, “little brain”) controls bodily coordination, balance, and muscle tone, as well as some aspects of memory involving procedure-related movements (see Chapters 7 and 8) (Middleton & Helms Tillery, 2003). The Hindbrain The prenatal development of the human brain within each individual roughly corresponds to the evolutionary development of the human brain within the species as a whole. Specifically, the hindbrain is evolutionarily the oldest and most primitive part of the brain. It also is the first part of the brain to develop prenatally. The midbrain is a relatively newer addition to the brain in evolutionary terms. It is the next part of the brain to develop prenatally. Finally, the forebrain is the most recent evolutionary addition to the brain. It is the last of the three portions of the brain to develop prenatally. The Hindbrain Additionally, across the evolutionary development of our species, humans have shown an increasingly greater proportion of brain weight in relation to body weight. However, across the span of development after birth, the proportion of brain weight to body weight declines. The Hindbrain For cognitive psychologists, the most important of these evolutionary trends is the increasing neural complexity of the brain. The evolution of the human brain has offered us the enhanced ability to exercise voluntary control over behavior. It has also strengthened our ability to plan and to contemplate alternative courses of action. Cerebral Cortex and Localization of Function The cerebral cortex plays an extremely important role in human cognition. The volume of the human skull has more than doubled over the past 2 million years, allowing for the expansion of the brain, and especially the cortex (Toro et al., 2008). The complexity of brain function increases with the cortical area. The human cerebral cortex enables us to think. Cerebral Cortex and Localization of Function The cortex comprises 80% of the human brain (Kolb & Whishaw, 1990). Because of it, we can plan, coordinate thoughts and actions, perceive visual and sound patterns, and use language. Without it, we would not be human. Cerebral Cortex and Localization of Function The surface of the cerebral cortex is grayish. It is sometimes referred to as gray matter. This is because it primarily comprises the grayish neural-cell bodies that process the information that the brain receives and sends. In contrast, the underlying white matter of the brain’s interior comprises mostly white, myelinated axons. Cerebral Cortex and Localization of Function The cerebral cortex forms the outer layer of the two halves of the brain—the left and right cerebral hemispheres (Davidson & Hugdahl, 1995; Galaburda & Rosen, 2003; Gazzaniga & Hutsler, 1999; Levy, 2000). Although the two hemispheres appear to be quite similar, they function differently. Cerebral Cortex and Localization of Function The left cerebral hemisphere is specialized for some kinds of activity whereas the right cerebral hemisphere is specialized for other kinds. Cerebral Cortex and Localization of Function The receptors on the left side generally transmit information to the right hemisphere. Similarly, the left hemisphere of the brain directs the motor responses on the right side of the body. The right hemisphere directs responses on the left side of the body Cerebral Cortex and Localization of Function However, not all information transmission is contralateral—from one side to another (contra-, “opposite”; lateral, “side”). Some ipsilateral transmission—on the same side— occurs as well. Cerebral Cortex and Localization of Function For example, odor information from the right nostril goes primarily to the right side of the brain. About half the information from the right eye goes to the right side of the brain, the other half goes to the left side of the brain. In addition to this general tendency for contralateral specialization, the hemispheres also communicate directly with one another. Cerebral Cortex and Localization of Function The corpus callosum is a dense aggregate of neural fibers connecting the two cerebral hemispheres (Witelson, Kigar, & Walter, 2003). It allows transmission of information back and forth. Once information has reached one hemisphere, the corpus callosum transfers it to the other hemisphere. Cerebral Cortex and Localization of Function If the corpus callosum is cut, the two cerebral hemispheres—the two halves of the brain—cannot communicate with each other (Glickstein & Berlucchi, 2008). Although some functioning, like language, is highly lateralized, most functioning— even language—depends in large part on integration of the two hemispheres of the brain. Cerebral Cortex and Localization of Function If the corpus callosum is cut, the two cerebral hemispheres—the two halves of the brain—cannot communicate with each other (Glickstein & Berlucchi, 2008). Although some functioning, like language, is highly lateralized, most functioning— even language—depends in large part on integration of the two hemispheres of the brain. Hemispheric Specialization The study of hemispheric specialization in the human brain can be traced back to Marc Dax, a country doctor in France. By 1836, Dax had treated more than 40 patients suffering from aphasia—loss of speech— as a result of brain damage. In studying his patients’ brains after death, Dax saw that in every case there had been damage to the left hemisphere of the brain. Hemispheric Specialization In 1861, French scientist Paul Broca claimed that an autopsy revealed that an aphasic stroke patient had a lesion in the left cerebral hemisphere of the brain. By 1864, Broca was convinced that the left hemisphere of the brain is critical in speech, a view that has held up over time. The specific part of the brain that Broca identified, now called Broca’s area, contributes to sp Hemispheric Specialization In 1861, French scientist Paul Broca claimed that an autopsy revealed that an aphasic stroke patient had a lesion in the left cerebral hemisphere of the brain. By 1864, Broca was convinced that the left hemisphere of the brain is critical in speech, a view that has held up over time. The specific part of the brain that Broca identified, now called Broca’s area, contributes to sp Hemispheric Specialization Another important early researcher, German neurologist Carl Wernicke, studied language- deficient patients who could speak but whose speech made no sense. Like Broca, he traced language ability to the left hemisphere. He studied a different precise location, now known as Wernicke’s area, which contributes to language comprehension. Broca’s area, contributes to speech. Wernicke’s area, which contributes to language comprehension. Hemispheric Specialization Despite the valuable early contributions by Broca, Wernicke, and others, the individual most responsible for modern theory and research on hemispheric specialization was Nobel Prize–winning psychologist Roger Sperry. Sperry (1964) argued that each hemisphere behaves in many respects like a separate brain. Hemispheric Specialization Some of the most interesting information about how the human brain works, and especially about the respective roles of the hemispheres, has emerged from studies of humans with epilepsy in whom the corpus callosum has been severed. Hemispheric Specialization Split-brain patients are people who have undergone operations severing the corpus callosum. Split-brain research reveals fascinating possibilities regarding the ways we think. Many in the field have argued that language is localized in the left hemisphere. Spatial visualization ability appears to be largely localized in the right hemisphere (Farah, 1988a, 1988b; Gazzaniga, 1985). Spatial-orientation tasks also seem to be localized in the right hemisphere (Vogel, Bowers, & Vogel, 2003). Hemispheric Specialization It appears that roughly 90% of the adult population has language functions that are predominantly localized within the left. Hemispheric Specialization There are indications, however, that the lateralization of left-handers differs from that of right-handers, and that for females, the lateralization may not be as pronounced as for males (Vogel, Bowers, & Vogel, 2003). Lateralization means localization of function or activity (as of verbal processes in the brain) on one side of the body in preference to the other. Hemispheric Specialization More than 95% of right-handers and about 70% of left-handers have left hemisphere dominance for language. In people who lack left- hemisphere processing, language development in the right hemisphere retains phonemic and semantic abilities, but it is deficient in syntactic competence (Gazzaniga & Hutsler, 1999) Phonology focuses on the organization of sounds, whereas Semantics focuses on studying the meanings of words. Syntax studies how words, phrases, and clauses are structured to form complex sentences. Hemispheric Specialization The left hemisphere is important not only in language but also in movement. People with apraxia—disorders of skilled movements—often have had damage to the left hemisphere. Such people have lost the ability to carry out familiar purposeful movements like forming letters when writing by hand (Gazzaniga & Hutsler, 1999; Heilman, Coenen, & Kluger, 2008). Hemispheric Specialization Another role of the left hemisphere is to examine past experiences to find patterns. Finding patterns is an important step in the generation of hypotheses (Wolford, Miller, & Gazzaniga, 2000). Hemispheric Specialization The right hemisphere is largely “mute” (Levy, 2000). It has little grammatical or phonetic understanding. But it does have very good semantic knowledge. It also is involved in practical language use. Hemispheric Specialization People with right-hemisphere damage tend to have deficits in following conversations or stories. They also have difficulties in making inferences from context and in understanding metaphorical or humorous speech (Levy, 2000). Hemispheric Specialization The right hemisphere also plays a primary role in self-recognition. In particular, the right hemisphere seems to be responsible for the identification of one’s own face (Platek et al., 2004). Hemispheric Specialization It seems that the left hemisphere is controlling their verbal processing (speaking) of visual information. The right hemisphere appears to control spatial processing (pointing) of visual information. Hemispheric Specialization Gazzaniga (Gazzaniga & LeDoux, 1978) does not believe that the two hemispheres function completely independently but rather that they serve complementary roles. For instance, there is no language processing in the right hemisphere (except in rare cases of early brain damage to the left hemisphere). Rather, only visuospatial processing occurs in the right hemisphere. Hemispheric Specialization The right hemisphere is dominant in our comprehension and exploration of spatial relations. Hemispheric Specialization Gazzaniga (1985) argues that the brain, and especially the right hemisphere of the brain, is organized into relatively independent functioning units that work in parallel. While these various independent and often subconscious operations are taking place, the left hemisphere tries to assign interpretations to these operations. Sometimes the left hemisphere perceives that the individual is behaving in a way that does not intrinsically make any particular sense Hemispheric Specialization For example, if you see an adult staggering along a sidewalk at night in a way that does not initially make sense, you may conclude he is drunk or otherwise not in full control of his senses. The brain thus finds a way to assign some meaning to that behavior. Hemispheric Specialization Levy (1974) has found some evidence that the left hemisphere tends to process information analytically (piece-by-piece, usually in a sequence). She argues that the right hemisphere tends to process it holistically (as a whole). Lobes of the Cerebral Hemispheres Lobes of the Cerebral Hemispheres For practical purposes, four lobes divide the cerebral hemispheres and cortex into four parts. They are not distinct units. Rather, they are largely arbitrary anatomical regions divided by fissures. Particular functions have been identified with each lobe, but the lobes also interact. Lobes of the Cerebral Hemispheres The frontal lobe, toward the front of the brain, is associated with motor processing and higher thought processes, such as abstract reasoning, problem solving, planning, and judgment (Stuss & Floden, 2003). It tends to be involved when sequences of thoughts or actions are called for. It is critical in producing speech. The prefrontal cortex, the region toward the front of the frontal lobe, is involved in complex motor control and tasks that require integration of information over time (Gazzaniga, Ivry, & Mangun, 2002). Lobes of the Cerebral Hemispheres The parietal lobe, at the upper back portion of the brain, is associated with somatosensory processing. It receives inputs from the neurons regarding touch, pain, temperature sense, and limb position when you are perceiving space and your relationship to it—how you are situated relative to the space you are occupying (Culham, 2003; Gazzaniga, Ivry, & Mangun, 2002). The parietal lobe is also involved in consciousness and paying attention. If you are paying attention to what you are reading, your parietal lobe is activated. Lobes of the Cerebral Hemispheres The parietal lobe lies between the occipital lobe and the central sulcus, a deep groove in the surface of the cortex (see Figure 3.23). The area just posterior to the central sulcus, the postcentral gyrus, or primary somatosensory cortex, receives sensations from touch receptors, muscle-stretch receptors, and joint receptors. Brain surgeons sometimes use only local anesthesia—that is, anesthetizing the scalp but leaving the brain awake. If during this process they lightly stimulate the postcentral gyrus, people report tingling sensations on the opposite side of the body Lobes of the Cerebral Hemispheres The temporal lobe, directly under your temples, is associated with auditory processing (Murray, 2003) and comprehending language. It is also involved in your retention of visual memories. For example, if you are trying to keep in memory, then your temporal lobe is involved. The temporal lobe also matches new things you see to what you have retained in visual memory. Lobes of the Cerebral Hemispheres The temporal lobe also contributes to complex aspects of vision, including perception of movement and recognition of faces. A tumor in the temporal lobe may give rise to elaborate auditory or visual hallucinations, whereas a tumor in the occipital lobe ordinarily evokes only simple sensations, such as flashes of light. When psychiatric patients report hallucinations, brain scans detect much activity in the temporal lobes (Dierks et al., 1999). Lobes of the Cerebral Hemispheres The occipital lobe is associated with visual processing (De Weerd, 2003b). The occipital lobe contains numerous visual areas, each specialized to analyze specific aspects of a scene, including color, motion, location, and form (Gazzaniga, Ivry, & Mangun, 2002). When you go to pick strawberries, your occipital lobe is involved in helping you find the red strawberries in between the green leaves. Lobes of the Cerebral Hemispheres Projection areas are the areas in the lobes in which sensory processing occurs. These areas are referred to as projection areas because the nerves contain sensory information going to (projecting to) the thalamus. Lobes of the Cerebral Hemispheres It is from here that the sensory information is communicated to the appropriate area in the relevant lobe. Similarly, the projection areas communicate motor information downward through the spinal cord to the appropriate muscles via the peripheral nervous system (PNS). Lobes of the Cerebral Hemispheres The frontal lobe, located toward the front of the head (the face), plays a role in judgment, problem solving, personality, and intentional movement. It contains the primary motor cortex, which specializes in the planning, control, and execution of movement, particularly of movement involving any kind of delayed response. If your motor cortex were electrically stimulated, you would react by moving a corresponding body part. The nature of the movement would depend on where in the motor cortex your brain had been stimulated. Lobes of the Cerebral Hemispheres Control of the various kinds of body movements is located contralaterally on the primary motor cortex. A similar inverse mapping occurs from top to bottom. The lower extremities of the body are represented on the upper (toward the top of the head) side of the motor cortex, and the upper part of the body is represented on the lower side of the motor cortex. Lobes of the Cerebral Hemispheres Information going to neighboring parts of the body also comes from neighboring parts of the motor cortex. Thus, the motor cortex can be mapped to show where and in what proportions different parts of the body are represented in the brain. Maps of this kind are called “homunculi” (homunculus is Latin for “little person”) because they depict the body parts of a person mapped on the brain. Lobes of the Cerebral Hemispheres Lobes of the Cerebral Hemispheres The three other lobes are located farther away from the front of the head. These lobes specialize in sensory and perceptual activity. For example, in the parietal lobe, the primary somatosensory cortex receives information from the senses about pressure, texture, temperature, and pain. It is located right behind the frontal lobe’s primary motor cortex. If your somatosensory cortex were electrically stimulated, you probably would report feeling as if you had been touched. Lobes of the Cerebral Hemispheres The relationship of function to form applies in the development of the motor cortex. The same holds true for the somatosensory cortex regions. The more need we have for use, sensitivity, and fine control in a particular body part, the larger the area of cortex generally devoted to that part. For example, we humans are tremendously reliant on our hands and faces in our interactions with the world. We show correspondingly large proportions of the cerebral cortex devoted to sensation in, and motor response by, our hands and face. Conversely, we rely relatively little on our toes for both movement and information gathering. As a result, the toes represent a relatively small area on both the primary motor and somatosensory cortices. Lobes of the Cerebral Hemispheres The region of the cerebral cortex pertaining to hearing is located in the temporal lobe, below the parietal lobe. This lobe performs complex auditory analysis. This kind of analysis is needed in understanding human speech or listening to a symphony. Lobes of the Cerebral Hemispheres The lobe also is specialized—some parts are more sensitive to sounds of higher pitch, others to sounds of lower pitch. The auditory region is primarily contralateral, although both sides of the auditory area have at least some representation from each ear. If your auditory cortex were stimulated electrically, you would report having heard some sort of sound. Lobes of the Cerebral Hemispheres The visual cortex is primarily in the occipital lobe. Some nerve fibers carry visual information ipsilaterally from each eye to each cerebral hemisphere; other fibers cross the optic chiasma and carry visual information contralaterally to the opposite hemisphere. Lobes of the Cerebral Hemispheres The brain is a very complex structure, and researchers use a variety of expressions to describe which part of the brain they are speaking of. These are the words rostral, ventral, caudal, and dorsal. They are all derived from Latin words and indicate the part of the brain with respect to other body parts. Rostral refers to the front part of the brain (literally the “nasal region”). Ventral refers to the bottom surface of the body/brain (the side of the stomach). Caudal literally means “tail” and refers to the back part of the body/brain. Dorsal refers to the upside of the brain (it literally means “back,” and in animals the back is on the upside of the body) Lobes of the Cerebral Hemispheres The visual cortex is primarily in the occipital lobe. Some nerve fibers carry visual information ipsilaterally from each eye to each cerebral hemisphere; other fibers cross the optic chiasma and carry visual information contralaterally to the opposite hemisphere. Neuronal Structure and Function Individual neural cells, called neurons, transmit electrical signals from one location to another in the nervous system (Carlson, 2006; Shepherd, 2004). The greatest concentration of neurons is in the neocortex of the brain. The neocortex is the part of the brain associated with complex cognition. This tissue can contain as many as 100,000 neurons per cubic millimeter (Churchland & Sejnowski, 2004). Neuronal Structure and Function The neocortex is the most recently evolved brain structure, as it appears only in mammals. This very thin (2–4 mm in humans), six-layered neuronal mantle covers the entire forebrain and it is the site of all cognitive functions, from the most basic to the most abstract. Neuronal Structure and Function Neurons vary in their structure, but almost all neurons have four basic parts, these include a soma (cell body), dendrites, an axon, and terminal buttons. Neuronal Structure and Function The soma, which contains the nucleus of the cell (the center portion that performs metabolic and reproductive functions for the cell), is responsible for the life of the neuron and connects the dendrites to the axon. Neuronal Structure and Function The many dendrites are branch-like structures that receive information from other neurons, and the soma integrates the information. Learning is associated with the formation of new neuronal connections Neuronal Structure and Function The single axon is a long, thin tube that extends (and sometimes splits) from the soma and responds to the information, when appropriate, by transmitting an electrochemical signal, which travels to the terminus (end), where the signal can be transmitted to other neurons. Neuronal Structure and Function Myelin is a white, fatty substance that surrounds some of the axons of the nervous system, which accounts for some of the whiteness of the white matter of the brain. Neuronal Structure and Function This sheath, which insulates and protects longer axons from electrical interference by other neurons in the area, also speeds up the conduction of information. Neuronal Structure and Function Nodes of Ranvier are small gaps in the myelin coating along the axon, which serve to increase conduction speed even more by helping to create electrical signals, also called action potentials, which are then conducted down the axon. Neuronal Structure and Function The terminal buttons are small knobs found at the ends of the branches of an axon that do not directly touch the dendrites of the next neuron. Rather, there is a very small gap, the synapse. Neuronal Structure and Function The synapse serves as a juncture between the terminal buttons of one or more neurons and the dendrites (or sometimes the soma) of one or more other neurons (Carlson, 2006). Synapses are important in cognition. Neuronal Structure and Function Rats show increases in both the size and the number of synapses in the brain as a result of learning (Federmeier, Kleim & Greenough, 2002). Decreased cognitive functioning, as in Alzheimer’s disease, is associated with reduced efficiency of synaptic transmission of nerve impulses (Selkoe, 2002). Neuronal Structure and Function Signal transmission between neurons occurs when the terminal buttons release one or more neurotransmitters at the synapse. Neuronal Structure and Function These neurotransmitters are chemical messengers for transmission of information across the synaptic gap to the receiving dendrites of the next neuron (von Bohlen und Halbach & Dermietzel, 2006). Neuronal Structure and Function At present, it appears that three types of chemical substances are involved in neurotransmission: monoamine neurotransmitters are synthesized by the nervous system through enzymatic actions on one of the amino acids (constituents of proteins, such as choline, tyrosine, and tryptophan) in our diet (e.g., acetylcholine, dopamine, and serotonin); amino-acid neurotransmitters are obtained directly from the amino acids in our diet without further synthesis (e.g., gamma- aminobutyric acid, or GABA); neuropeptides are peptide chains (molecules made from the parts of two or more amino acids). Monoamine Neurotransmitters Dopamine is associated with attention, learning, and movement coordination. Dopamine also is involved in motivational processes, such as reward and reinforcement. Schizophrenics show very high levels of dopamine. This fact has led to the “dopamine theory of schizophrenia” which suggests that high levels of dopamine may be partially responsible for schizophrenic conditions. Drugs used to combat schizophrenia often inhibit dopamine activity (von Bohlen und Halbach & Dermietzel, 2006). Monoamine Neurotransmitters In contrast, patients with Parkinson’s disease show very low dopamine levels, which leads to the typical trembling and movement problems associated with Parkinson’s. When patients receive medication that increases their dopamine level, they (as well as healthy people who receive dopamine) sometimes show an increase in pathological gambling. Gambling is a compulsive disorder that results from impaired impulse control. When dopamine treatment is suspended, these patients no longer exhibit this behavior (Drapier et al., 2006; Voon et al., 2007; Abler et al., 2009). These findings support the role of dopamine in motivational processes and impulse control. Monoamine Neurotransmitters Serotonin plays an important role in eating behavior and body- weight regulation. High serotonin levels play a role in some types of anorexia. Specifically, serotonin seems to play a role in the types of anorexia resulting from illness or treatment of illness. For example, patients suffering from cancer or undergoing dialysis often experience a severe loss of appetite (Agulera et al., 2000; Davis et al., 2004). This loss of appetite is related, in both cases, to high serotonin levels. Serotonin is also involved in aggression and regulation of impulsivity (Rockland, 2000). Drugs that block serotonin tend to result in an increase in aggressive behavior. Monoamine Neurotransmitters Histamine. Histamine regulates body functions including wakefulness, feeding behavior and motivation. Histamine plays a role in asthma, bronchospasm, mucosal edema and multiple sclerosis. Monoamine Neurotransmitters Epinephrine. Epinephrine (also called adrenaline) and norepinephrine (see below) are responsible for your body’s so- called “fight-or-flight response” to fear and stress. These neurotransmitters stimulate your body’s response by increasing your heart rate, breathing, blood pressure, blood sugar and blood flow to your muscles, as well as heighten attention and focus to allow you to act or react to different stressors. Too much epinephrine can lead to high blood pressure, diabetes, heart disease and other health problems. As a drug, epinephrine is used to treat anaphylaxis, asthma attacks, cardiac arrest and severe infections. Monoamine Neurotransmitters Norepinephrine. Norepinephrine (also called noradrenaline) increases blood pressure and heart rate. It’s most widely known for its effects on alertness, arousal, decision-making, attention and focus. Many medications (stimulants and depression medications) aim to increase norepinephrine levels to improve focus or concentration to treat ADHD or to modulate norepinephrine to improve depression symptoms. Monoamine Neurotransmitters Acetylcholine is associated with memory functions, and the loss of acetylcholine through Alzheimer’s disease has been linked to impaired memory functioning in Alzheimer’s patients (Hasselmo, 2006). Acetylcholine also plays an important role in sleep and arousal. When someone awakens, there is an increase in the activity of so-called cholinergic neurons in the basal forebrain and the brainstem (Rockland, 2000) Monoamine Neurotransmitters This excitatory neurotransmitter does a number of functions in your central nervous system (CNS [brain and spinal cord]) and in your peripheral nervous system (nerves that branch from the CNS). Acetylcholine is released by most neurons in your autonomic nervous system regulating heart rate, blood pressure and gut motility. Acetylcholine plays a role in muscle contractions, memory, motivation, sexual desire, sleep and learning. Imbalances in acetylcholine levels are linked with health issues, including Alzheimer’s disease, seizures and muscle spasms. Amino-acid Neurotransmitters Glutamate. This is the most common excitatory neurotransmitter of your nervous system. It’s the most abundant neurotransmitter in your brain. It plays a key role in cognitive functions like thinking, learning and memory. Imbalances in glutamate levels are associated with Alzheimer’s disease, dementia, Parkinson’s disease and seizures. Amino-acid Neurotransmitters Gamma-aminobutryic acid (GABA). GABA is the most common inhibitory neurotransmitter of your nervous system, particularly in your brain. It regulates brain activity to prevent problems in the areas of anxiety, irritability, concentration, sleep, seizures and depression. Amino-acid Neurotransmitters Glycine. Glycine is the most common inhibitory neurotransmitter in your spinal cord. Glycine is involved in controlling hearing processing, pain transmission and metabolism. Peptide Neurotransmitters Endorphins. Endorphins are your body’s natural pain reliever. They play a role in our perception of pain. Release of endorphins reduces pain, as well as causes “feel good” feelings. Low levels of endorphins may play a role in fibromyalgia and some types of headaches. Peptide Neurotransmitters Oxytocin is a hormone and a neurotransmitter that is associated with empathy, trust, sexual activity, and relationship-building. It is sometimes referred to as the “love hormone,” because levels of oxytocin increase during hugging and orgasm. Excitatory. Excitatory neurotransmitters “excite” the neuron and cause it to “fire off the message,” meaning, the message continues to be passed along to the next cell. Examples of excitatory neurotransmitters include glutamate, epinephrine and norepinephrine. Inhibitory. Inhibitory neurotransmitters block or prevent the chemical message from being passed along any farther. Gamma-aminobutyric acid (GABA), glycine and serotonin are examples of inhibitory neurotransmitters. Modulatory. Modulatory neurotransmitters influence the effects of other chemical messengers. They “tweak” or adjust how cells communicate at the synapse. They also affect a larger number of neurons at the same time. Receptors and Drugs Receptors in the brain that normally are occupied by the standard neurotransmitters can be hijacked by psychopharmacologically active drugs, legal or illegal. Receptors and Drugs Drugs that we might ingest—either for medical reasons or recreationally—can act like neurotransmitters to influence our thoughts, feelings, and behavior. An agonist is a drug that has chemical properties similar to a particular neurotransmitter and thus mimics the effects of the neurotransmitter. Receptors and Drugs As an example, cocaine is an agonist for the neurotransmitter dopamine. Because dopamine produces feelings of pleasure when it is released by neurons, cocaine creates similar feelings when it is ingested. Receptors and Drugs An antagonist is a drug that reduces or stops the normal effects of a neurotransmitter. When an antagonist is ingested, it binds to the receptor sites in the dendrite, thereby blocking the neurotransmitter. As an example, the poison curare is an antagonist for the neurotransmitter acetylcholine. When the poison enters the brain, it binds to the dendrites, stops communication among the neurons, and usually causes death. Viewing the Structures and Functions of the Brain Scientists can use many methods for studying the human brain. These methods include both postmortem (from Latin, “after death”) studies and in vivo (from Latin, “living”) techniques on both humans and animals. Portmortem Studies Postmortem studies and the dissection of brains have been done for centuries. Even today, researchers often use dissection to study the relation between the brain and behavior. Portmortem Studies After the patients die, the researchers examine the patients’ brains for lesions—areas where body tissue has been damaged, such as from injury or disease. Then the researchers infer that the lesioned locations may be related to the behavior that was affected. Portmortem Studies Through such investigations, researchers may be able to trace a link between an observed type of behavior and anomalies in a particular location in the brain. An early example is Paul Broca’s (1824–1880) famous patient, Tan (so named because that was the only syllable he was capable of uttering). Tan had severe speech problems. These problems were linked to lesions in an area of the frontal lobe (Broca’s area). This area is involved in certain functions of speech production. Portmortem Studies This area is involved in certain functions of speech production. In more recent times, postmortem examinations of victims of Alzheimer’s disease (an illness that causes devastating losses of memory;) have led researchers to identify some of the brain structures involved in memory (e.g., the hippocampus). Studying non human animals To obtain single-cell recordings, researchers insert a very thin electrode next to a single neuron in the brain of an animal (usually a monkey or a cat). They then record the changes in electrical activity that occur in the cell when the animal is exposed to a stimulus. Studying non human animals Studying non human animals A second group of animal studies includes selective lesioning—surgically removing or damaging part of the brain—to observe resulting functional deficits (Al’bertin, Mulder, & Wiener, 2003; Mohammed, Jonsson, & Archer, 1986). Studying non human animals A third way of doing research with animals is by employing genetic knockout procedures. By using genetic manipulations, animals can be created that lack certain kinds of cells or receptors in the brain. Comparisons with normal animals then indicate what the function of the missing receptors or cells may be. Studying non human animals Gene knockouts (also known as gene deletion or gene inactivation) are a widely used genetic engineering technique that involves the targeted removal or inactivation of a specific gene within an organism's genome. Studying live humans These techniques—electrical recordings, static imaging, and metabolic imaging—are described in this section. Studying live humans Electroencephalograms (EEGs) are recordings of the electrical frequencies and intensities of the living brain, typically recorded over relatively long periods (Picton & Mazaheri, 2003). Through EEGs, it is possible to study brain wave activity indicative of changing mental states such as deep sleep or dreaming. To obtain EEG recordings, electrodes are placed at various points along the surface of the scalp. The electrical activity of underlying brain areas is then recorded. Studying live humans Studying live humans An event-related potential (ERP) is the record of a small change in the brain’s electrical activity in response to a stimulating event. The fluctuation typically lasts a mere fraction of a second. ERPs provide very good information about the time- course of task-related brain activity. Studying live humans Some studies of mental abilities like selective attention have investigated individual differences by using event-related potentials (e.g., Troche et al., 2009). ERP methods are also used to examine language processing. Studying live humans ERP can be used to examine developmental changes in cognitive abilities. These experiments provide a more complete understanding of the relationship between brain and cognitive development (Taylor & Baldeweg, 2002). Studying live humans An event related potential (ERP) is a transient fluctuation in the brain's electrical field generated by neural activity and induced, in language studies, by the presentation of a visual or auditory language stimulus. Studying live humans Computed tomography (CT or CAT). Unlike conventional X-ray methods that only allow a two-dimensional view of an object, a CT scan consists of several X-ray images of the brain taken from different vantage points that, when combined, result in a three-dimensional image. Studying live humans Studying live humans Healthcare providers use CT scans to see things that regular X-rays can’t show. For example, body structures overlap on regular X-rays and many things aren’t visible. A CT shows the details of each of your organs for a clearer and more precise view. Studying live humans A CT scan takes pictures of your: Bones. Muscles. Organs. Blood vessels.  Studying live humans CT scans help healthcare providers detect various injuries and diseases, including: 1. Certain types of cancer and benign (noncancerous) tumors. 2. Fractures (broken bones). 3. Heart disease. 4. Blood clots. 5. Bowel disorders (appendicitis, diverticulitis, blockages, Crohn’s disease). 6. Kidney stones. 7. Brain injuries. 8. Spinal cord injuries. 9. Internal bleeding. Studying live humans The aim of an angiography is not to look at the structures in the brain, but rather to examine the blood flow. When the brain is active, it needs energy, which is transported to the brain in the form of oxygen and glucose by means of the blood. In angiography, a dye is injected into an artery that leads to the brain, and then an X-ray image is taken. Studying live humans Studying live humans The magnetic resonance imaging (MRI) scan is of great interest to cognitive psychologists. The MRI reveals high-resolution images of the structure of the living brain by computing and analyzing magnetic changes in the energy of the orbits of nuclear particles in the molecules of the body. Studying live humans There are two kinds of MRIs—structural MRIs and functional MRIs. Structural MRIs provide images of the brain’s size and shape whereas functional MRIs visualize the parts of the brain that are activated when a person is engaged in a particular task. Studying live humans Studying live humans MRI scanners are particularly well suited to image the non-bony parts or soft tissues of the body. The brain, spinal cord and nerves, as well as muscles, ligaments, and tendons are seen much more clearly with MRI than with regular x-rays and CT; for this reason MRI is often used to image knee and shoulder injuries. Studying live humans Positron emission tomography (PET) scans measure increases in oxygen consumption in active brain areas during particular kinds of information processing (O’Leary et al., 2007; Raichle, 1998, 1999). Studying live humans A positron emission tomography (PET) scan is a type of imaging test. It uses a radioactive substance called a tracer to look for disease in the body. A PET scan shows how organs and tissues are working. This is different than MRI and CT scans. These tests show the structure of, and blood flow to and from organs. Studying live humans The most common use for a PET scan is for cancer, when it may be done: To see how far cancer has spread. This helps to select the best treatment approach. To check how well your cancer is responding, either during treatment or after treatment is completed. Studying live humans Functional magnetic resonance imaging (fMRI) is a neuroimaging technique that uses magnetic fields to construct a detailed representation in three dimensions of levels of activity in various parts of the brain at a given moment in time. This technique builds on MRI, but it uses increases in oxygen consumption to construct images of brain activity. The basic idea is the same as in PET scans. Studying live humans However, the fMRI technique does not require the use of radioactive particles. Rather, the participant performs a task while placed inside an MRI machine. This machine typically looks like a tunnel. When someone is wholly or partially inserted in the tunnel, he or she is surrounded by a donut-shaped magnet. Studying live humans This technique is less invasive than PET. It also has higher temporal resolution— measurements can be taken for activity lasting fractions of a second, rather than only for activity lasting minutes to hours. Studying live humans In fact, for a single scan, PET has a better signal-to-noise ratio (SNR) than fMRI. However, overall fMRI provides a clearer image as fMRI can be repeated multiple times due to its lack of radiation exposure. Studying live humans The fMRI technique can identify regions of the brain active in many areas, such as vision (Engel et al., 1994; Kitada et al., 2010), attention (Cohen et al.; 1994; Samanez-Larkin et al., 2009), language (Gaillard et al., 2003; Stein et al., 2009), and memory (Gabrieli et al., 1996; Wolf, 2009). Studying live humans Transcranial magnetic stimulation (TMS) temporarily disrupts the normal activity of the brain in a limited area. Therefore, it can imitate lesions in the brain or stimulate brain regions. Studying live humans An advantage to TMS is that it is possible to examine causal relationships with this method because the brain activity in a particular area is disrupted and then its influence on task- performance is observed; most other methods allow the investigator to examine only correlational relationships by the observation of brain function (Gazzaniga, Ivry, & Mangun, 2009). Studying live humans Studying live humans Transcranial magnetic stimulation (TMS) is a procedure that uses magnetic fields to stimulate nerve cells in the brain to improve symptoms of major depression. It's called a "noninvasive" procedure because it's done without using surgery or cutting the skin. Studying live humans Magnetoencephalography (MEG) measures activity of the brain from outside the head (similar to EEG) by picking up magnetic fields emitted by changes in brain activity. This technique allows localization of brain signals so that it is possible to know what different parts of the brain are doing at different times. It is one of the most precise of the measuring methods. MEG is used to help surgeons locate pathological structures in the brain (Baumgartner, 2000). Studying live humans It allows the measurement of ongoing brain activity on a millisecond-by-millisecond basis, and it shows where in the brain activity is produced. Brain Disorders A number of brain disorders can impair cognitive functioning. Brain disorders can give us valuable insight into the functioning of the brain. Stroke Vascular disorder is a brain disorder caused by a stroke. Strokes occur when the flow of blood to the brain undergoes a sudden disruption. People who experience stroke typically show marked loss of cognitive functioning. The nature of the loss depends on the area of the brain that is affected by the stroke. There may be paralysis, pain, numbness, a loss of speech, a loss of language comprehension, impairments in thought processes, a loss of movement in parts of the body, or other symptoms. Stroke Two kinds of stroke may occur (NINDS stroke information page, 2009). An ischemic stroke usually occurs when a buildup of fatty tissue occurs in blood vessels over a period of years, and a piece of this tissue breaks off and gets lodged in arteries of the brain. Ischemic strokes can be treated by clot-busting drugs. Stroke The second kind of stroke, a hemorrhagic stroke, occurs when a blood vessel in the brain suddenly breaks. Blood then spills into surrounding tissue. As the blood spills over, brain cells in the affected areas begin to die. This death is either from the lack of oxygen and nutrients or from the rupture of the vessel and the sudden spilling of blood. The prognosis for stroke victims depends on the type and severity of damage. Stroke Those who suffer ischemic strokes have a much better chance for survival than those who experience hemorrhagic strokes, as hemorrhagic stroke not only damages brain cells but also may lead to increased pressure on the brain or spasms in the blood vessels Stroke Symptoms of stroke appear immediately on the occurrence of stroke. Typical symptoms include (NINDS stroke information page, 2009): numbness or weakness in the face, arms, or legs (especially on one side of the body) confusion, difficulty speaking or understanding speech vision disturbances in one or both eyes dizziness, trouble walking, loss of balance or coordination severe headache with no known cause Brain Tumors Brain tumors, also called neoplasms, can affect cognitive functioning in very serious ways. Tumors can occur in either the gray or the white matter of the brain. Tumors of the white matter are more common (Gazzaniga, Ivry, & Mangun, 2009). Brain Tumors Two types of brain tumors can occur. Primary brain tumors start in the brain. Most childhood brain tumors are of this type. Secondary brain tumors start as tumors somewhere else in the body, such as in the lungs. Brain tumors can be either benign or malignant. Brain Tumors Benign tumors do not contain cancer cells. They typically can be removed and will not grow back. Cells from benign tumors do not invade surrounding cells or spread to other parts of the body. However, if they press against sensitive areas of the brain, they can result in serious cognitive impairments. They also can be life-threatening, unlike benign tumors in most other parts of the body. Brain Tumors Malignant brain tumors, unlike benign ones, contain cancer cells. They are more serious and usually threaten the victim’s life. They often grow quickly. They also tend to invade surrounding healthy brain tissue. In rare instances, malignant cells may break away and cause cancer in other parts of the body. Brain Tumors Following are the most common symptoms of brain tumors (What you need to know about brain tumors, 2009): headaches (usually worse in the morning) nausea or vomiting changes in speech, vision, or hearing problems balancing or walking changes in mood, personality, or ability to concentrate problems with memory muscle jerking or twitching (seizures or convulsions) numbness or tingling in the arms or legs Brain Tumors The diagnosis of brain tumor is typically made through neurological examination, CT scan, and/or MRI. The most common form of treatment is a combination of surgery, radiation, and chemotherapy. Head Injuries Head injuries result from many causes, such as a car accident, contact with a hard object, or a bullet wound. Head injuries are of two types. In closed-head injuries, the skull remains intact but there is damage to the brain, typically from the mechanical force of a blow to the head. Slamming one’s head against a windshield in a car accident might result in such an injury. In open-head injuries, the skull does not remain intact but rather is penetrated, for example, by a bullet. Head injuries are surprisingly common. Head Injuries Loss of consciousness is a sign that there has been some degree of damage to the brain as a result of the injury. Damage resulting from head injury can include spastic movements, difficulty in swallowing, and slurring of speech, among many other cognitive problems. Head Injuries Immediate symptoms of a head injury include (Signs and symptoms, 2009): unconsciousness abnormal breathing obvious serious wound or fracture bleeding or clear fluid from the nose, ear, or mouth disturbance of speech or vision pupils of unequal size weakness or paralysis dizziness neck pain or stiffness seizure vomiting more than two to three times loss of bladder or bowel control Generally, brain damage can result from many causes. When brain damage occurs, it always should be treated by a medical specialist at the earliest possible time. A neuropsychologist may be called in to assist in diagnosis, and rehabilitation psychologists can be helpful in bringing the patient to the optimal level of psychological functioning possible under the circumstances Intelligence and Neuroscience Intelligence and Brain Size One line of research looks at the relationship of brain size or volume to intelligence (see Jerison, 2000; Vernon et al., 2000; Witelson, Beresh, & Kiga, 2006). The evidence suggests that, for humans, there is a modest but significant statistical relationship between brain size and intelligence (Gignac, Vernon, & Wickett, 2003; McDaniel, 2005). The amount of gray matter in the brain is strongly correlated with IQ in many areas of the frontal and temporal lobes (Haier, Jung, Yeo, Head, & Alkire, 2004). Intelligence and Neuroscience Intelligence and Brain Size However, the brain areas that are correlated with IQ appear to differ in men versus women. Frontal areas are of relatively more importance in women, whereas posterior areas are of relatively more importance in men, even if both genders are matched for intelligence (Haier, Jung, Yeo, Head, & Alkire, 2005). Intelligence and Neurons Several studies initially suggested that speed of conduction of neural impulses may correlate with intelligence, as measured by IQ tests (McGarry- Roberts, Stelmack, & Campbell, 1992; Vernon & Mori, 1992). Intelligence and Neurons Surprisingly, neural conduction velocity appears to be a more powerful predictor of IQ scores for men than for women. So gender differences may account for some of the differences in the data (Wickett & Vernon, 1994). As of now, the results are inconsistent (Haier, 2010). Intelligence and Brain Metabolism That is, smarter brains consume less sugar and therefore expend less effort than less smart brains doing the same task. Furthermore, cerebral efficiency increases as a result of learning on a relatively complex task involving visuospatial manipulations, for example, the computer game Tetris (Haier et al., 1992). As a result of practice, more intelligent participants not only show lower cerebral glucose metabolism overall but also show more specifically localized metabolism of glucose. Intelligence and Brain Metabolism On the other hand, another study found, contrary to the earlier findings, that smarter participants had increased glucose metabolism relative to their average comparison group (Larson et al., 1995). Biological Bases of Intelligence Testing Damage to the posterior regions of the brain seems to have negative effects on measures of crystallized intelligence (Gray & Thompson, 2004; Kolb & Whishaw, 1996; Piercy, 1964). In patients with frontal lobe damage, impairments in fluid intelligence are observed (Duncan, Burgess, & Emslie, 1995; Gray, Chabris, & Braver, 2003; Gray & Thompson, 2004). Biological Bases of Intelligence Testing Other research highlights the importance of the parietal regions for performance on general and fluid intelligence tasks (Lee et al., 2006; see also Glaescher et al., 2009). The P-FIT Theory of Intelligence The discovered importance of the frontal and parietal regions in intelligence tasks has led to the development of an integrated theory of intelligence that highlights the importance of these areas. This theory, called the parietal-frontal integration theory (P-FIT), stresses the importance of interconnected brain regions in determining differences in intelligence. The regions this theory focuses on are the prefrontal cortex, the inferior and superior parietal lobe, the anterior cingulated cortex, and portions of the temporal and occipital lobes (Colom et al., 2009; Jung & Haier, 2007). The P-FIT Theory of Intelligence P-FIT theory describes patterns of brain activity in people with different levels of intelligence; it cannot, however, explain what makes a person intelligent or what intelligence is. The P-FIT Theory of Intelligence We cannot realistically study a brain or its contents and processes in isolation without also considering the entire human being. We must consider the interactions of that human being with the entire environmental context within which the person acts intelligently. Many researchers and theorists urge us to take a more contextual view of intelligence. Furthermore, some alternative views of intelligence attempt to broaden the definition of intelligence to be more inclusive of people’s varied abilities.