Unit 3 B Biological Bases of Behavior:The Brain




The brain’s increasing complexity arises from new brain systems built on top of old. Within the brainstem are the oldest regions, the medulla and the reticular formation. The thalamus sits atop the brainstem and the cerebellum extends from the rear. The limbic system includes the amygdala, the hippocampus, and the hypothalamus. The cerebral cortex, representing the highest level of brain development, is responsible for our most complex functions.
Each hemisphere of the cerebral cortex has four geographical areas: the frontal, parietal, occipital, and temporal lobes. Although small, well-defined regions within these lobes control muscle movement and receive information from the body senses, most of the cortex—its associationareas—are free to process other information. Experiments on split-brain patients suggest that, for most people, the left hemisphere is the more verbal and the right hemisphere excels in visual perception and the recognition of emotion. Studies of people with intact brains indicate that each hemisphere makes unique contributions to the integrated functions of the brain. Consciousness is our awareness of ourselves and our environment. Cognitive neuroscientists study the links between brain activity and mental processes. Research indicates that we have a two-track mind. Conscious information processing enables us to exercise control and to communicate
our mental states to others. Beneath the surface, unconscious processing occurs simultaneously on many parallel tracks. Our awareness focuses on a limited aspect of all that we experience.



Studying the Brain


The oldest method of studying the brain involved observing the effects of brain diseases and injuries. Powerful new techniques now reveal brain structures and activities in the living brain. By surgically lesioning and electrically stimulating specific brain areas, by recording electrical activity on the brain’s surface (EEG), and by looking inside the living brain to see its activity (CT, PET, MRI, and fMRI), neuroscientists examine the connections between brain, mind, and behavior.

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Older Brain Structures


The brainstem, the brain’s oldest and innermost region, is responsible for automatic survival functions. It includes the medulla, which controls heartbeat and breathing, and the reticular formation, which plays an important role in controlling arousal. Just above the medulla sits the pons, which helps coordinate movements.Atop the brainstem is the thalamus, the brain’s sensory switchboard.
It receives information from all the senses, except smell, and sends it to the higher brain regions that deal with seeing, hearing, tasting, and touching. The cerebellum, attached to the rear of the brainstem, coordinates voluntary movement (with the help of the pons) and balance and helps process sensory information. It also enables one type of nonverbal learning and memory and helps us judge time, modulate our emotions, and discriminate sounds and textures.

These older brain functions all occur without any conscious effort. This illustrates a recurring theme: Our brain processes most information outside of our awareness.

The limbic system has been linked primarily to memory, emotions, and drives. For example, one of its neural centers, the hippocampus, processes memory. Another, the amygdala, influences aggression and fear. A third, the hypothalamus, has been linked to various bodily maintenance functions and to pleasurable rewards. Its hormones influence the pituitary gland, and thus it provides a major link between the nervous and endocrine systems.


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The Cerebral Cortex


The cerebral cortex, a thin surface layer of interconnected neural cells, is our body’s ultimate control and information-processing center. Glial cells support, nourish, and protect the nerve cells of the cerebral cortex. The frontal lobes, just behind the forehead, are involved in speaking, muscle movements, and planning and making judgments. The parietal lobes, at the top of head and toward the rear, receive sensory input for touch and body position. The occipital lobes, at the back of the head, include visual areas. The temporal lobes, just above the ears, include auditory areas. Each lobe performs many functions and interacts with other areas of the cortex.

The motor cortex, an arch-shaped region at the rear of the frontal lobes, controls voluntary muscle movements on the opposite side of the body. Body parts requiring the most precise control occupy the greatest amount of cortical space. In an effort to find the source of motor control, researchers have recorded messages from brain areas involved in planning and intention, leading to the testing of neural prosthetics for paralyzed patients. The sensory cortex, a region at the front of the parietal lobes, registers and processes body sensations. The most sensitive body parts require the largest amount of space in the sensory cortex.


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The association areas are not involved in primary motor or sensory functions. Rather, they integrate and act on information processed by the sensory areas. They are involved in higher mental functions, such as learning, remembering, thinking, and speaking. Association areas are found in all four lobes. Complex human abilities, such as memory and language, result from the intricate coordination of many brain areas.

Language depends on a chain of events in several brain regions. When we read aloud, the words (1) register in the visual area, (2) are relayed to the angular gyrus, which transforms the words into auditory code, which is (3) received and understood in nearby Wernicke’s area and sent (4) to Broca’s area, which (5) controls the motor cortex as it creates the pronounced word. Depending on which link in this chain is damaged, a different form of aphasia occurs. For example, damage to the angular gyrus leaves the person able to speak and understand but unable to read. Damage to Wernicke’s area disrupts understanding. Damage to Broca’s area disrupts speaking. What we experience as a continuous experience is the visible tip of a subdivided information-processing iceberg, most of which is outside our awareness. More generally, language processing illustrates how the mind’s subsystems are localized in particular brain regions, yet the brain acts as a unified whole.

Research indicates that some neural tissue can reorganize in response to damage. When one brain area is damaged, others may in time take over some of its function. For example, if you lose a finger, the sensory cortex that received its input will begin to receive input from the adjacent fingers, which become more sensitive. Our brains are most plastic when we are young children.

Constraint-induced therapy rewires the brain by restraining a fully functioning limb and forcing use of the “bad hand” or the uncooperative leg. Eventually, the therapy reprograms the brain, improving the dexterity of a brain-damaged child or even an adult stroke victim. New evidence reveals that adult humans can also generate new brain cells. Monkey brains illustrate neurogenesis by forming thousands of new neurons each day.


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Our Divided Brain


A split brain is one in which the corpus callosum, the wide band of axon fibers that connects the two brain hemispheres, has been severed. Experiments on split-brain patients have refined our knowledge of each hemisphere’s special functions (called hemispheric specialization or lateralization). In the laboratory, investigators ask a split-brain patient to look at a designated spot, then send information to either the left or right hemisphere (by flashing it to the right or left visual field).


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Right-Left Differences in the Intact Brain


Quizzing each hemisphere separately, researchers have confirmed that for most people, the left hemisphere is the more verbal and the right hemisphere excels in visual perception and the recognition of emotion. Studies of people with intact brains have confirmed that the right and left hemispheres each make unique contributions. For example, the left hemisphere makes quick, literal interpretations of language, and the right hemisphere excels in making inferences.

About 10 percent of us are left-handed. Almost all right-handers process speech primarily in the left hemisphere. Left-handers are more diverse. Seven in ten process speech in the left hemisphere and the rest either process speech in the right hemisphere or use both hemispheres. Left-handers are more numerous among those with reading disabilities, allergies, and migraine headaches. Lefthandedness
is also more common among musicians, mathematicians, professional baseball and cricket players, architects, and artists. The advantages and disadvantages of being a lefty seem roughly equal.


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The Brain and Consciousness


Consciousness is our awareness of ourselves and our environment. Cognitive neuroscience, the interdisciplinary study of how brain activity is linked with our mental processes, is helping us to understand how specific brain states relate to conscious experiences. Most cognitive neuroscientists are exploring and mapping the conscious functions of the cortex. Based on our cortical activation patterns, they are beginning to “read our minds.” For example, they can tell which of 10 similar objects we are viewing.

Cognitive neuroscientists and others studying the brain activity underlying consciousness have discovered a two-track human mind, each with its own neural processing. Perception, memory, thinking, language, and attitudes all operate on two levels—a conscious, deliberate “high road” and an unconscious, automatic “low road.” Researchers call this dual processing. Conscious information processing enables us to exert voluntary control and to communicate our mental states to others. Beneath the surface, faster unconscious processing occurs simultaneously on many parallel tracks. Clearly, much of our everyday thinking, feeling, and acting occurs outside our conscious awareness.


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*Work Cited:  All summary notes come from *Myers Pyschology for AP, Lecture Guides (2011 Worth Publishers)