CHAPTER 4:

NEUROSCIENCE AND BEHAVIOR

General

• Everything psychological is simultaneously biological.

• We think, feel, and act with our bodies. • By studying the links between biology and

psychology, biological psychologists are gaining new clues to sleep and dreams, depression and schizophrenia, hunger and sex, stress and disease.

• In the 1800s, Franz Gall invented phrenology, a popular theory that claimed that bumps on the skull reveal our mental abilities and our character traits.

• Although bumps on the skull reveal nothing abut the brain’s underlying functions, Gall was accurate in supposing that various brain regions have particular functions.

Neural Communication

We are composed of biological, psychological, and social-cultural systems that interact.

Psychologists study how these systems work together to shape our behavior.

At all levels, researchers examine how we take in information; organize, interpret, and store it; and use it.

The information systems of humans and other animals operate similarly.

• For example, although the human brain is more complex than a rat’s, both follow the same principles.

• This similarity permits researchers to study relatively simple animals to discover how our neural systems operate.

Figure 2.2 A motor neuronMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Neurons• A neuron consists of a cell body and

branching fibers:– The dendrite fibers receive information from

sensory receptors or other neurons– the axon fibers pass that information along to

other neurons. – A layer of fatty tissue, called the myelin

sheath, insulates the axons of some neurons and helps speed their impulses.

Neuron’s Response

• A neural impulse fires when the neuron is stimulated by pressure, heat, light, or chemical messages from adjacent neurons.

• Received signals trigger an impulse only if the excitatory signals minus the inhibitory signals exceeds a minimum intensity called the threshold.

• The neuron’s reaction is an all-or-none response.

©John Wiley & Sons, Inc. 2007 Huffman: Psychology

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Neural Bases of Psychology: The Structure of a Neuron

• The impulse, called the action potential, is a brief electrical charge that travels down the axon rather like manhole covers flipping open.

• During the resting potential, the fluid interior of the axon carries mostly negatively charged atoms (ions) while the fluid outside has mostly positively charged atoms.

• Then, the first bit of the axon is depolarized (its selectively permeable surface allows positive ions in), and the electrical impulse travels down the axon as channels open, admitting ions with a positive charge.

• When these channels close, others open and positive ions are pumped back out, restoring the neuron to its polarized state.

Nerve Cell Communication

• When electrical impulses reach the axon terminal, they stimulate the release of chemical messengers called neurotransmitters that cross the junction between neurons called the synapse.

Table 2.1Myers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

• After these molecules traverse the tiny synaptic gap between neurons, they combine with receptor sites on neighboring neurons, thus passing on their excitatory or inhibitory messages.

• The sending neuron, in a process called reuptake, normally absorbs the excess neurotransmitter molecules in the synaptic gap.

• Different neurotransmitters have different effects on behavior and emotion. For example, the neurotransmitter acetylcholine (ACh) plays a crucial role in learning and memory.

• Found at every junction between a motor neuron and skeletal muscle, ACh causes the muscle to contract. The brain’s endorphins, natural opiates released in response to pain and vigorous exercise, explain the “runner’s high” and the indifference to pain in some injured people.

Impact of Drug Use

• When the brain is flooded with opiate drugs such as heroin and morphine, it may stop producing its own natural opiates, and withdrawal of these drugs may result in discomfort until the brain resumes production of its natural opiates.

• Some drugs (agonists), such as some of the opiates, mimic a natural neurotransmitter’s effects or block its reuptake.

• Others (antagonists), such as botulin, inhibit a particular neurotransmitter’s release or block its effects.

• Researchers have used information about brain neurotransmitters in their efforts to create therapeutic drugs, such as those used to alleviate depression and schizophrenia.

• The problem is that the blood-brain barrier enables the brain to fence out unwanted chemicals.

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Nervous System Organization

The Nervous System

• Neurons communicating with other neurons form our body’s primary system, the nervous system.

• The brain and spinal cord form the central nervous system (CNS).

• The peripheral nervous system (PNS) links the central nervous system with the body’s sense receptors, muscles, and glands. The axons carrying this PNS information are bundled into the electrical cables we know as nerves.

• Sensory neurons send information from the body’s tissues and sensory organs inward to the brain and spinal cord, which process the information.

• Motor neurons carry outgoing information from the central nervous system to the body’s tissues.

• Interneurons in the central nervous system communicate internally and intervene between the sensory inputs and the motor outputs.

The Peripheral Nervous System

• The somatic nervous system of the peripheral nervous system enables voluntary control of our skeletal muscles.

• The autonomic nervous system of the peripheral nervous system is a dual self-regulating system that influences the glands and muscles of our internal organs.

• The sympathetic nervous system arouses; • The parasympathetic nervous system calms.

Reflex Pathways

• Reflexes, simple, automatic responses to stimuli, illustrate the spinal cord’s work.

• A simple reflex pathway is composed of a single sensory neuron and a single motor neuron, which often communicate through an interneuron.

• For example, when our fingers touch a candle’s flame, information from the skin receptors travels inward via a sensory neuron to a spinal cord interneuron, which sends a signal outward to the arm muscles via a motor neuron. Because this reflex involves only the spinal cord, we jerk our hand away before the brain creates an experience of pain.

• Neurons in the brain cluster into work groups called neural networks.

• The cells in each layer of a neural network connect with various cells in the next layer.

• With experience, networks can learn, as feedback strengthens or inhibits connections that produce certain results.

• One network is interconnected with other networks, which are distinguished by their specific functions.

The Endocrine System

• The endocrine system’s glands secrete hormones, chemical messengers produced in one tissue that travel through the bloodstream and affect other tissues, including the brain.

• Compared to the speed at which messages move through the nervous system, endocrine messages move more slowly but their effects are usually longer-lasting.

• The endocrine system’s hormones influence many aspects of our lives, including growth, reproduction, metabolism, and mood, keeping everything in balance while responding to stress, exertion, and internal thoughts.

• In a moment of danger, the adrenal glands release the hormones epinephrine and norepinephrine, which increase heart rate, blood pressure, and blood sugar, providing us with increased energy.

• The pituitary gland is the endocrine system’s most influential gland. Under the influence of the brain’s hypothalamus, the pituitary’s secretions influence growth and the release of hormones by other endocrine glands.

• These may in turn influence both the brain and behavior and thus reveal the intimate connection of the nervous and endocrine systems.

Studying the Brain

• The oldest method of studying the brain involved observing the effects of brain diseases and injuries.

• But MRI (magnetic resonance imaging) scans now reveal brain structures, and electroencephalogram (EEG), PET (positron emission tomography), and fMRI (functional MRI) recordings reveal activities in the living brain.

• By surgically lesioning and electrically stimulating specific brain areas, by recording electrical activity on the brain’s surface, and by displaying activity with computer-aided brain scans, neuroscientists examine the connections between brain, mind, and behavior.

Figure 2.16 The brainstem and thalamusMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Components of the Brainstem

• The brainstem, the brain’s oldest and innermost region, is responsible for automatic survival functions.

• It includes the: – medulla, which controls heartbeat and

breathing;– reticular formation, which plays an important

role in controlling arousal.

• 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 movement output 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.

Figure 2.17 The brain’s organ of agilityMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

The Limbic System

• The limbic system has been linked primarily to memory, emotions, and drives.

• For example, one of its neural centers, the hippocampus, helps process memories.

• 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.

Figure 2.18 The limbic systemMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

©John Wiley & Sons, Inc. 2007 Huffman: Psychology

in Action (8e)

A Tour Through The Brain (Continued)

• Limbic System: interconnected group of forebrain structures involved with emotions, drives, and memory

The Cerebral Cortex • The cerebral cortex is a thin sheet of cells

composed of billions of nerve cells and their countless interconnections. It is the body’s ultimate control and information-processing center.

• Glial cells support, nourish, and protect the nerve cells of the cerebral cortex.

• Each lobe performs many functions and interacts with other areas of the cortex.

Figure 2.25 The cortex and its basic subdivisionsMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

• 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.

Figure 2.32 Specialization and integration in languageMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Figure 2.33 Brain activity when hearing, seeing, and speaking wordsMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

Figure 2.23 Brain structures and their functionsMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

The Motor Cortex and The Sensory 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 Motor Cortex and The Sensory Cortex

• 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.

• The association areas are not involved in primary motor or sensory functions. Rather, they interpret, 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.

Describe the five brain areas that would be involved if you read this sentence aloud.

• Language depends on a chain of events in several brain regions. When we read the sentence aloud, the words – (1) register in the visual area

– (2) are relayed to the angular gyrus which transforms the words into an auditory code, which is

– (3) received and understood in the nearby Wernicke’s area and

– (4) sent 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

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A Tour Through The Brain: The Motor

Cortex and Somatosensory

Cortex

The Brain’s Plasticity

• Research indicates that some neural tissue can reorganize in response to injury or 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.

• New evidence reveals that adult humans can also generate new brain cells.

• Our brains are most plastic when we are young children. In fact, children who have had an entire hemisphere removed still lead normal lives.

The Split-Brain

• A split brain is one whose 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.

Figure 2.35 The corpus callosumMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

• 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).

• Quizzing each hemisphere separately, the 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 to the integrated functioning of the brain.

• On occasion, hemispheric specialization, called lateralization, has been shown to occur.

Brain Organization, Handedness, and Mortality.

• About 10 percent of us are left-handed.• Almost all right-handers process speech primarily

in the left hemisphere. • Left-handers are more diverse. • More than half process speech in the left

hemisphere, about a quarter in the right, and the last quarter use both hemispheres equally.

• The finding that the percentage of left-handers declines dramatically with age led researchers to examine the leftie’s health risks.

• Left-handers are more likely to have experienced birth stress, such as prematurity or the need for assisted respiration.

• They also endure more headaches, have more accidents, use more tobacco and alcohol, and suffer more immune system problems.

• However, researchers continue to debate whether left-handers have a lower life expectancy.

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A Tour Through The Brain: Lateralization

• The left and right hemispheres of the

brain each specialize

in particular operations.

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Our Genetic Inheritance• To answer questions about the influence of

nature versus nurture, psychologists use behavioral genetics research.

• Behavioral Genetics: studies the relative effects of nature (heredity, genes, and chromosomes) and nurture (environment) on behavior and mental processes.

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Our Genetic Inheritance: Genes & DNA

• The nucleus of every cell in our body contains genes, which carry the code for hereditary transmission. These genes are arranged along chromosomes (strands of paired DNA).

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Our Genetic Inheritance: Twin Research

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Our Genetic Inheritance Evolutionary Psychology:

studies how natural selection and adaptation help explain behavior and mental processes

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Our Genetic Inheritance: Better Living Through

Neuroscience• Neuroplasticity: brain’s lifelong ability to

reorganize and change its structure and function

• Neurogenesis: the division and differentiation of non-neuronal cells to produce neurons

• Stem cells: Precursor (immature) cells that give birth to new specialized cells

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Chromosome, DNA, Gene, & Genome

• Every cell nucleus contains the genetic master code for the body.

• Within each cell are 46 chromosomes with 23 donated by each parent.

• Each chromosome is composed of a coiled chain of a molecule, called DNA (deoxyribonucleic acid).

• Genes are DNA segments that, when “turned on,” form templates for the production of proteins.

66Figure 3.1 The genes: Their location and compositionMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

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Chromosome, DNA, Gene, & Genome

• We inherit one set of 23 chromosomes from each parent.

• The two sets form pairs that contain alternate genes for the same traits.

• Sometimes, one gene is dominant and “overrides” the recessive gene. For example, in the determination of eye color, the brown-eye gene is dominant.

• Genome: complete set of genetic material

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• By directing the manufacture of proteins, the approximately 30,000 genes that compose the human body determine our individual biological development.

• The genome provides the complete instructions for making an organism, consisting of all the genetic material in the organism’s chromosomes.

• Variations at particular gene sites in the DNA define each person’s uniqueness.

• Human traits are influenced by gene complexes, that is, by many genes acting in concert.

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Genes & Twins

• Comparisons of identical twins, who are genetic clones, and fraternal twins, who develop from separate eggs, help behavior geneticists tease apart the effects of heredity and environment.

• Research findings show that identical twins are much more similar than fraternals in abilities, personality traits, and even interests.

• Genes matter!!!!

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• The discovery that identical twins separated at birth show remarkable similarities also suggests genetic influence.

• Indeed, separated fraternal twins do not exhibit similarities comparable to those of separated identical twins. Genes also influence the social effects of such traits.

• Identical twins are more likely to both share similar risk for developing Alzheimer’s and of experiencing divorce

71Figure 3.2 Same fertilized egg, same genes; different eggs, different genesMyers: Psychology, Eighth EditionCopyright © 2007 by Worth Publishers

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Adoption Studies

• Adoption studies enable comparisons with both genetic and environmental relatives.

• Adoptees’ traits & personality bear more similarities to their biological parents than to their caregiving adoptive parents.

• Nonetheless, the latter do influence their children’s attitudes, values, manners, faith, and politics.

• Clearly nature and nurture shape one’s developing personality.

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Adoption Studies

• Adoptive parents are least likely to influence personality traits.

• They are more likely to influence attitudes, moral values, religious values, etc.

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Temperament Stability

• An infant’s temperament includes inborn emotional excitability.

• From the first weeks of life, some babies are more relaxed and cheerful, while others are more tense and irritable.

• These differences in temperament tend to endure. For example, the most emotionally intense preschoolers tend to be relatively intense as young adults.

• Compared with fraternal twins, identical twins have more similar temperaments.

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Heritability

• Using twin and adoption methods, behavior geneticists can mathematically estimate the heritability of any trait—the extent to which variation among individuals is due to their differing genes.

• If the heritability of intelligence is 50 percent, this does not mean that one’s intelligence is 50 percent genetic.

• Instead it means that we can attribute to genetic influence 50 percent of the observed variation among people.

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• The heritability of a specific trait may vary, depending on the range of populations and environments studied.

• As environments become more similar, heredity as a source of differences becomes more important.

• Our genes affect how our environment reacts to and influences us.

• Nature enables nurture.

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• Heritable individual differences need not imply heritable group differences.

• Genes and environment work together. Because of human adaptability, most psychologically interesting traits are expressed in particular environments.

• In other words, genes are self-regulating; they can react differently in different environments.

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Genetically Influenced Trait

• We are all the products of interactions between our genetic predispositions and our surrounding environments.

• A baby who is genetically predisposed to be social and easygoing may, in contrast to one who is less so, attract more affectionate and stimulating care and thus develop into a warmer and more outgoing person.

• Similarly, a stressful environment can trigger genes that affect the production of neurotransmitters that underlie depression.

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Genetically Influenced Trait

• Genes respond to environments

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Genetically Influenced Trait

• There is now a large body of evidence that supports the conclusion that individual differences in most, if not all, reliably measured psychological traits, normal and abnormal, are substantially influenced by genetic factors.”

• Big Five (extraversion, agreeableness, conscientiousness, neuroticism, and openness) and the Big Three (positive emotionality, negative emotionality, and constraint), is in the range of 40 to 50 percent

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Genetically Influenced Trait

• Shared environmental factors are the dominant influence on IQ

• Psychological Interests = .36• Psychiatric Illnesses:

• Schizophrenia = .80• Depression = .40• Anxiety Disorders = .20 to .40 • Alcoholism = .50 to .60• Antisocial Personality Disorder = .41 to .46

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Genetically Influenced Trait

• Does childhood maltreatment may produce an antisocial adult?

• those with high-active monoamine oxidase A (MOA) genes are virtually immune to the effects of maltreatment

• Those with low-active genes are much more antisocial if maltreated, yet slightly less antisocial if not maltreated.

• In short, maltreatment alone does not produce antisocial behavior; the low-active gene must also be present.