Gazzaniga • Heatherton • Halpern
Psychological Science
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
– Central nervous system (CNS): brain and spinal
– 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
• 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
– 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
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
• All-or-none principle: A neuron will either fire or
• 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
“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
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
– 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
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
• 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
– 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
• 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
• 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
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
• 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
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
The Peripheral Nervous System
Includes the Somatic
and Autonomic Systems
• The peripheral nervous system has two primary
– 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
• 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
• 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
• 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
• 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
• Discovered clues to the mechanisms responsible for
• 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
• 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 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
• Behavioral genetics: the study of how genes and
environment interact to influence psychological
• 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
• Greater similarity of monozygotic twins (raised
together or apart) is likely due to genetic
– 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
• 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
• 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
How Does the Brain Change?
• Despite the great precision and the specificity
of its connections, the brain is extremely
• Plasticity: a property of the brain that allows it
to change as a result of experience, drugs, or
“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
• 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
– 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
– 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
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.

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