Gazzaniga • Heatherton • Halpern Psychological Science FOURTH EDITION Chapter 3 Biology and Behavior ©2013 W. W. Norton & Company, Inc. “Threat and Politics: Are Political Views Rooted in Biology?” If you’ve ever been in an argument with someone who had different political views, chances are neither of you won. Maybe it’s not just stubbornness. New research has found that people with strong opposing political views might also have very different physical responses to threat. Biology and Behavior • Huntingon’s disease is a deadly genetic disorder that affects the brain • After psychologist Lenore Wexler’s mother died of Huntington’s, she changed her research from the clinical to the biological area and eventually discovered the genetic marker for the disease • She decided not to take the test that may have identified her as having the gene (would you take the test?) • To know what makes us who we are, we need to understand the physiological processes and genetic underpinnings of our thoughts, feelings, and behavior 3.1 How Does the Nervous System Operate? • Distinguish between the functions of distinct types of neurons. • Describe the structure of the neuron. • Describe the electrical and chemical changes that occur when neurons communicate. • Identify the major neurotransmitters and their primary functions. How Does the Nervous System Operate? • The nervous system is responsible for everything we think, feel, and do • Basic components: – Neurons: receive, integrate, and transmit information in the nervous system; form neural networks – Central nervous system (CNS): brain and spinal cord – Peripheral nervous system (PNS): all other nerve cells in the body Neurons Are Specialized for Communication • Nerve cells are powered by electrical impulses; communicate with other nerve cells through chemical signals • Three basic phases: – Reception: Chemical signals are received from neighboring neurons – Integration: Incoming signals are assessed – Transmission: Signals are passed on to other receiving neurons Types of Neurons • Sensory (afferent) neurons: detect information from the physical world and pass that information along to the brain – Somatosensory nerves provide information from the skin and muscles • Motor neurons: direct muscles to contract or relax • Interneurons: communicate within local or short-distance circuits “Baby Scent and Dads” Even the toughest dads can get warm and fuzzy when it comes to their kids. Now researchers studying monkeys have found that’s not just an attitude, it’s a physical response to the mere scent of their infant. This ScienCentral News video explains. “The Scent of a Man” Is male body odor sexy or stinky? Turns out your answer to that question depends on differences in a single gene. This ScienCentral News video explains a research finding that could help answer the long-standing mystery of whether human odors serve as social or sexual signals. Neuron Structure • • • • • Dendrite: detects chemical signals from neighboring neurons Cell body (soma): collects and integrates information Axon: transmitselectrical impulses Terminal buttons: bulbous end of an axon Synapse: supports chemical communication between neurons – Synaptic cleft: narrow gap between terminal button (presynaptic membrane) and dendrite (postsynaptic membrane) of neighboring neuron • Myelin sheath: encases and insulates axons – Composed of glial cells – Nodes of Ranvier: Spaces between glial cells The Resting Membrane Potential is Negatively Charged • Resting membrane potential: The ratio of negative to positive ions is greater inside the neuron than outside – Polarized: when a neuron has more negative ions inside it than outside – Polarization: creates the electrical energy necessary to power the firing of the neuron The Roles of Sodium and Potassium Ions • Sodium ions and potassium ions contributeto a neuron’s resting membrane potential. • Ions pass through the cell membrane channels • Flow of ions through each channel is controlled by a gating mechanism • Sodium-potassium pump: increases potassium outside the neuron; decreases sodium inside the neuron Action Potentials Cause Neural Communication • Action potential (neural firing): the electrical signal that passes along the axon and causes the release of chemicals that transmit signals to other neurons Changes in Electrical Potential Lead to Action • Neurons receive chemical signals from nearby neurons – Excitatory signals depolarize the cell membrane (i.e., reduce polarization), increasing the likelihood that the neuron will fire – Inhibitory signals hyperpolarize the cell (i.e., increase polarization), decreasing the likelihood that the neuron will fire • When a neuron fires, the inside of the neuron becomes slightly more positively charged than the outside • After firing, the inside of the neuron returns to its slightly negative resting state Action Potentials Spread Along to Axon • Depolarization travels along an axon like a wave in movement called propagation • Action potentials always move away from the cell body to the terminal buttons. • Insulation provided by the myelin sheath enables the action potential to skip quickly along the axon • Multiple sclerosis: De-myelinated axons slow down neural impulses All-Or-None Principle • Neuronal firing is determined by the number and frequency of signals it receives • An action potential occurs when the sum of excitatory and inhibitory signals leads to a change in voltage that exceeds the neuron’s firing threshold. • All-or-none principle: A neuron will either fire or not • Neurons fire with the same potency each time; they do not fire in a way that can be described as weak or strong Neurotransmitters Bind to Receptors across the Synapse • Action potentials cause presynapticneurons to release chemicals called neurotransmitters from terminal buttons • Chemicals travel across the synaptic cleft and, like a key fitting a lock, are received by receptors on the postsynaptic neurons’ dendrites • The binding of a neurotransmitter with a receptor produces an excitatory or inhibitorysignal “Sudden Sleep” Researchers have discovered a chemical brain process that may explain why some people fall asleep without warning. The research was done in mice, but as this ScienCentral News video reports, it helps explain what regulates our normal sleep patterns and may lead to future treatments of narcolepsy. Neurotransmitters Bind With Specific Receptors • Neurotransmitters stimulate specific receptors and block new signals until terminated • The effects (excitatory/inhibitory) of a neurotransmitter are a function of the receptors that the neurotransmitters bind to • Events that terminate the neurotransmitter’s influence in the synaptic cleft are: – Reuptake:Neurotransmitter is reabsorbed into the presynaptic terminal buttons – Enzyme deactivation: Enzyme destroys the neurotransmitter – Autoreceptors:signal the presynaptic neuron to stop releasing the neurotransmitter Neurotransmitters Influence Mental Activity and Behavior • Much of what we know about neurotransmitters has been learned through the study of the effects of drugs and toxins on emotion, thought, and behavior • Drugs and toxins can alter neurotransmitter action: – Agonists:enhance the actions of neurotransmitters – Antagonists:inhibit the actions of neurotransmitters • Researchers often inject agonists or antagonists into animals’ brains to assess how neurotransmitters affect behavior Types of Neurotransmitters • There are many kinds of neurotransmitters • Nine of them are particularly important in understanding how we think, feel, and behave 3.2 What Are the Basic Brain Structures and Their Functions? • Identify the basic structures of the brain and their primary functions. “Biased Brains” Is it possible to have racial biases without even knowing it? Research on a primitive part of the brain suggests it. As this ScienCentral News video explains, a new experiment shows that just putting biases into words may help us overcome them. What Are the Basic Brain Structures and Their Functions? • The adult human brain is best viewed as a three-pound collection of interacting neural circuits • Gall &Spurzheim proposed their theory of phrenology, based on the idea that the brain operates through functional localization • Karl Lashley built his research on the general idea of equipotentiality • Broca (1861) provided the first strong evidence that brain regions perform specialized functions (Broca’s area) • Modern imaging techniques have greatly advanced our understanding of the human brain The Brain Stem Houses the Basic Programs of Survival • The spinal cord: coordination of reflexes; carries sensory information to the brain and motor signals away from the brain • Composed of two types of tissue: gray matter and white matter • Brain stem:medulla oblongata, pons, midbrain, reticular formation The Cerebellum Is Essential for Movement • Cerebellum (little brain): extremely important for proper motor function, learning, and motor memory • Damage to its different parts produces different effects: – Damage to lobes on either side causes a loss of limb coordination – Damage to the nodes at the very bottom causes balance problems • Cerebellum is activated when a person experiences a painful stimulus or observes a loved one receiving that stimulus, which means the cerebellum may be involved in the experience of empathy Subcortical Structures Control Emotions and Appetitive Behaviors • The forebrain consists of the two cerebral hemispheres, right and left • The most noticeable feature of the forebrain is the convoluted surface of the cerebral cortex • Subcortical structures that lie below the cerebral cortex include: Hypothalamus, thalamus, hippocampus, amygdala, and basal ganglia • Some of these structures belong to the limbic system, whichcontrols appetitive behaviors and emotion Hypothalamus • The hypothalamus is the brain’s master regulatory structure • Affects the functions of many internal organs, regulating body temperature, body rhythms, blood pressure, and blood glucose levels • Also involved in many motivated behaviors, including thirst, hunger, aggression, and lust Thalamus • The thalamus is the gateway to the cortex • Excepting smell, it receives all incoming sensory information, organizes it, and relays it to the cortex • During sleep, the thalamus partially shuts the gate on incoming sensations while the brain rests Hippocampus and Amygdala • The hippocampus (Greek, “sea horse”) plays an important role in the storage of new memories – Recently shown to grow larger with increased use; may be involved in how we remember the arrangements of both places and objects in space – Maguire and colleagues (2003) found that one region of the hippocampus in London taxi drivers’ brains was much larger than in most other London drivers’ brains • The amygdala(Latin, “almond”) serves a vital role in our learning to associate things in the world with negative and positive emotional responses The Basal Ganglia • Basal ganglia:crucial for planning and producing movement • Damage to the basal ganglia can produce tremors and rigidity, uncontrollable jerky movements, and can impair the learning of movements and habits • Contains the nucleus accumbens, which is important for experiencing reward and motivating behavior The Cerebral Cortex Underlies Complex Mental Activity • Cerebral cortex (Latin, “bark”): the outer layer of the cerebral hemispheres • It is the site of all thoughts, detailed perceptions, and complex behaviors • Each cerebral hemisphere has four “lobes”: Occipital, parietal, temporal, frontal • Corpus callosum: a bridge of axons connecting the hemispheres and permitting information to flow between them The Prefrontal Cortex in Close-Up • Phineas Gage: His accident led to major personality changes • Prefrontal cortex: brain region particularly concerned with social phenomena (e.g., following norms). Patients with injury to this region often have profound disturbances in their ability to get along with others • Lobotomy: deliberate damaging of the prefrontal cortex; used in the late 1940s early 1950s • Left patients lethargic and emotionally flat, and much easier to manage in mental hospitals, but it also left them disconnected from their social surroundings 3.3 How Does the Brain Communicate with the Body? • Differentiate between the divisions of the nervous system. • Identify the primary structures of the endocrine system. • Explain how the nervous system and the endocrine system communicate to control thought, feeling, and behavior. “Forgetting Fear” Whether we have unexplained phobias or fears that stem from a bad experience, most of us are afraid of something. But can we ever get over our fears? Scientists are looking for the answer—in our brains. This ScienCentral News video has more. The Peripheral Nervous System Includes the Somatic and Autonomic Systems • The peripheral nervous system has two primary components: – Somatic nervous system: transmits sensory signals to/from the central nervous system – Autonomic nervous system (ANS): regulates the body’s internal environment by stimulating glands and internal organs; carries signals from the glands and internal organs to the central nervous system Sympathetic and Parasympathetic Divisions • The autonomic nervous system has two divisions – Sympathetic division:prepares the body for action (e.g., fight or flight) – Parasympathetic division: returns the body to its normal, resting state • Most internal organs are controlled by inputs from sympathetic and parasympathetic systems • The more aroused (e.g., anxious) you are, the greater the sympathetic system’s dominance The Endocrine System Communicates through Hormones • The endocrine system is a communication network that influences thoughts, behaviors, and actions • The main difference is that whereas the nervous system uses electrochemical signals, the endocrine system uses hormones • Hormones: chemical substances released into the bloodstream by the ductless endocrine glands, such as the pancreas, thyroid, and testes or ovaries Hormones’ Effects on Sexual Behavior • Endocrine glands influencing sexual behavior are the gonads (testes, ovaries) • Gonadal hormones are identical in males and females, but: – Androgens (testosterone) are more prevalent in males. – Estrogens (estradiol, progesterone) are more prevalent in females • Removal of the gonads impacts sexual desire and in females, terminates estrus • When they are ovulating, heterosexual women find men who look and act masculine more attractive (Gangestad, Simpson, Cousins, Garver-Apgar, & Christensen, 2004) “Hungry for Love” Do you crave your valentine as much as you crave food and drink? Brain researchers may have discovered why. This ScienCentral News video has more. Actions of the Nervous System and the Endocrine System Are Coordinated • The endocrine system is under the central nervous system’s control • Neural activation causes the hypothalamus to secrete a particular releasing factor, which causes the pituitary gland to release a hormone specific to that factor • Pituitary gland (“master gland”): governs the release of hormones from the rest of the endocrine glands responsible for major bodily processes – Example: Growth hormone (GH) prompts bone, cartilage, and muscle tissue to grow or helps them regenerate after injury 3.4 What Is the Genetic Basis of Psychological Science? • Explain how genes are transmitted from parent to offspring • Discuss the goals and methods of behavioral genetics • Explain how both environmental factors and experience influence genetic expression What Is the Genetic Basis of Psychological Science? • The term genetics is typically used to describe how characteristics are passed along to offspring and to the processes involved in turning genes “on” and “off” • Genetic predispositions are important in determining the environments we select for ourselves • Biology and environment mutually influence each other “Evolving Brains” Battles over teaching evolution may be playing out near you. Meanwhile, scientists have new evidence that our most important organ—the brain—is still evolving. This ScienCentral New video has more. All of Human Development Has a Genetic Basis • The genome is the master blueprint for making an entire organism – “The genome provides the option, and the environment determines which option is taken” (Marcus, 2004) • Chromosomes: made of deoxyribonucleic acid (DNA), consisting of two intertwined strands of molecules in a double helix shape • Genes: segments of DNA strands • Human Genome Project: mapped the entire structure of human DNA “Addiction Gene” Genetics researchers have confirmed that people with a different form of a certain gene are more susceptible to drug and alcohol addiction. They hope the finding will help predict who might get hooked and what treatments will help those who do. This ScienCentral News video has more. Featuring: Wolfgang Sade, Ohio State University “Alcohol Withdrawal” Scientists have found a gene in mice that might control the symptoms alcoholics get when they stop drinking alcohol. This ScienCentral News video has more. Featuring: Sidney Strickland, Dean of Graduate and Postgraduate Studies, Rockefeller University Heredity Involves Passing Along Genes through Reproduction • Mendel (ca. 1866): cross-pollinated different colored pea plants to see which color flowers the plants would produce • Discovered clues to the mechanisms responsible for heredity • Dominant gene:expressed whenever it is present in either parent • Recessive gene:expressed only when it is matched with a similar gene from the other parent “Fearless Gene” Scientists have found a gene that may control whether or not someone is a risk taker. As this ScienCentral News video explains, the gene controls development of a specific part of your brain. Featuring: Jim Olson, Fred Hutchinson Cancer Institute Genotype and Phenotype • Genotype: an organism’s genetic makeup; never changes • Phenotype: an organism’s observable physical characteristics; always changing • Genetics (nature) and environment (nurture) both influence phenotype Polygenic Effects • Polygenic trait: a trait that is influenced by many genes • The range of skin tones among Americans shows that human skin color is not inherited the same way as flower color was in Mendel’s research • Skin tone is not the end product of a single dominant/recessive gene pairing (genotype) but rather shows the effects of multiple genes Genetic Variation Is Created by Sexual Reproduction • From any two parents, 8 million different combinations of the 23 chromosomes are possible • The human zygote grows through cell division; errors sometimes occur during cell division and lead to mutations • Mutations produce an ability or behavior that may be advantageous/disadvantageous to the organism “Nicotine like Heroin” Scientists studying how the brain reacts to smoking are finding more evidence that nicotine and heroin have similar effects. This ScienCentral News video reports that researchers at University of Chicago have found part of the brain that responds to smoking and heroin in much the same way. Genes Affect Behavior • A person’s abilities and psychological traits are influenced by the interaction of genes and environment • Behavioral genetics: the study of how genes and environment interact to influence psychological activity • People are born like “undeveloped photographs”: The image has been captured, but the way it eventually appears depends on the development process Behavioral Genetics Methods • Behavioral geneticists use two methods to assess the degree to which traits are inherited: – Twin studies: compare similarities between monozygotic (identical) and dizygotic (fraternal) twins to determine the genetic basis of specific traits • Greater similarity of monozygotic twins (raised together or apart) is likely due to genetic influence – Adoption studies: compare biological relatives and adoptive relatives “Twin DNA Differences” Geneticists are discovering that identical twins don’t have identical DNA. As this ScienCentral New video explains, this surprising research could help scientists better understand genetic diseases in the rest of us. Featuring: Julia and Claire Calzonetti, identical twins; Jan Dumanski, University of Alabama at Birmingham Understanding Heritability • Heritability: a statistical estimate of the genetic portion of the observed variation in some specific trait • Heritability refers to populations, not to individuals – Example: In a certain population, height has a heritability of .60, which means 60 percent of height variation among individuals in that population is genetic. It does not mean that any one individual gets 60 percent of his or her height from genetics and 40 percent from environment • Estimates of heritability are concerned only with the extent that people differ in terms of their genetic makeup within the group Social and Environmental Contexts Influence Genetic Expression • Caspi et al. (2002) followed more than 1,000 New Zealanders from birth until adulthood • Every few years information was collected about the participants • When the participants were 26 years old, investigators examined which factors predicted who had become a violent criminal • Mistreatment at home + low MAO gene accounted for nearly 50 percent of criminality • Study is a good example of how genes and social context interact to affect behavior (phenotype) Genetic Expression Can Be Modified • Gene manipulation techniques can enhance or reduce the expression of a particular gene; genes from one animal species can be inserted into the embryo of another • Changing a single gene can dramatically change behavior – Example: A gene from the highly social prairie vole was inserted into the developing embryos of normally antisocial mice. The resulting transgenic mice exhibited social behavior more typical of prairie voles (Insel& Young, 2001) • Changing one gene’s expression leads to the expression of other genes, which ultimately influences behavior 3.5 How Does the Brain Change? • Explain how environmental factors and experience influence brain organization. • Describe sex differences in brain structure and function. How Does the Brain Change? • Despite the great precision and the specificity of its connections, the brain is extremely malleable • Plasticity: a property of the brain that allows it to change as a result of experience, drugs, or injury “Live Learning” Have you ever wondered how babies learn to talk? As this ScienCentral News video reports, some researchers now think it’s more than just hearing the people around them. The Interplay of Genes and Environment Wires the Brain • Nature and nurture constantly interact to affect DNA’s activity and the products of that activity • Brain plasticity reflects the interactive nature of our biological and environmental influences Cell Identity Becomes Fixed Over Time • As an embryo develops, each cell becomes more and more committed to its identity • Tissue transplanted early enough completely transforms into whatever type is appropriate for its new location; transplanting cells too late may disfigure the organism • Many people are excited about the possibility of transplanting fetal cells because they are undeveloped enough to become any type of tissue Experience Fine-Tunes Neural Connections • Experience is important for normal brain development and maybe even more so for superior development • Example: – One group of rats was raised in a “normal” lab environment (featureless boxes with bedding at the bottom, plus dishes for food and water); another group was raised in an enriched environment – The “enriched” group developed bigger, heavier brains than the first group (Rosenzweig, Bennett, & Diamond, 1972) Culture Affects the Brain • Our cultural experiences contribute to different patterns of brain activity • Example: – One group of participants in Japan and another group in the United States were shown pictures of both neutral and fearful facial expressions portrayed by Japanese and American faces. – Activity in the amygdala was greatest when participants viewed fearful expressions within their own cultural group (Chiao et al., 2008) “Gay Choice?” Is sexual orientation predetermined by biology, or is it a chosen behavior? Attempts to answer that question scientifically tend to get mixed up with politics. But as this ScienCentral News video reports, a new book reveals that a controversial study on the issue has been widely misinterpreted. The Brain Rewires Itself throughout Life • Although brain plasticity decreases with age, the brain can grow new connections among neurons and even grow new neurons into very old age • The rewiring and growth within the brain represents the biological basis of learning “Brain Connections” Scientists have discovered that our brains go through not just growth spurts but also periods of pruning. This ScienCentral News video has more. Featuring: Bonnie Firestein, Rutgers University; Jay Giedd, national Institute of Mental Health Change in the Strength of Connections Underlies Learning • Changes in the brain due to experience are mainly in the strength of existing connections – Hebb’s “fire together, wire together” catchphrase: When two neurons fire simultaneously, the synaptic connection between them strengthens • Entirely new connections can grow between neurons. • Neurogenesis: New neurons are produced in some brain regions (e.g., the hippocampus) • Neurogenesis may underlie neural plasticity Changes in the Brain • Wiring in the brain is affected by amount of use (e.g., recall the London taxi drivers) • Phantom limb: the intense sensation that an amputated body part still exists • Phenomenon suggests that the brain has not reorganized in response to the injury and that the missing limb’s cortical representation remains intact • An amputee who has lost a hand may, when his or her eyes are closed, perceive a touch on the cheek as if it were on the missing hand (Ramachandran&Hirstein, 1998) The Puzzles of Synesthesia • Synesthesia: For synesthetes, sensory experiences are crossed – One man reported the he hates driving because the sight of road signs tastes to him like a mixture of pistachio ice cream and ear wax (McNeil, 2006) • The brain area involved in seeing colors is physically close to the brain area involved in understanding numbers, thus people with color/number synesthesia, may have some connections or cross-wiring between brain areas (Ramachandran& Hubbard, 2001) Females’ and Males’ Brains Are Similar and Different • Females and males differ in their life experiences and hormonal makeup, which leads to differences between their brains – Males tend to have larger brains – Females and males may solve some complex problems differently, with females using languagerelated brain regions and males using spatial-related brain regions (Haier et al., 2005) – Brain areas important in processing language are more likely to be found in both halves of females’ brains than in males’ brains “Men vs. Women Shoppers” Attention shoppers. Scientists have confirmed what many of us already know: most men buy, but most women shop. However, as this ScienCentral News video shows, the researchers also found that a shopper’s mind-set affects what he or she thinks about after shopping. “Shoppers’ Minds” Holiday shoppers beware. That pleasantly surprising sale price can actually bust your budget. A new study by a behavioral scientist shows why we often spend more when we’re convinced that we’re saving. This ScienCentral News video has more. The Brain Can Recover from Injury • Following an injury in the cortex, the surrounding gray matter assumes the function of the damaged area • Radical hemispherectomy: After the surgical removal of an entire cerebral hemisphere, the remaining hemisphere eventually takes on most of the lost hemisphere’s functions • One of the most exciting (and controversial) areas of neurological research is the transplantation of human fetal tissue (stem cells) into the brain to repair damage • Instead of using fetal stem cells, new methods are emerging that allow researchers to create stem cells by reprogramming adult cells “Exercise Your Brain” We know that exercise can help you feel younger, both physically and mentally. But as this ScienCentral News video reports, now there is evidence that aerobic exercise actually lends to a more youthful brain.