The Biological Bases of Behavior
(Chapters 2 and 4)
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Plato: the mind is
located in the brain
Franz Gall and
Phrenology
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Early 1800s
Read bumps on skull
to understand traits
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Everything we do is ultimately controlled by
our body and brain
Body/brain composed of cells
 Brain cells called neurons communicate electrically
and chemically
 Different parts of the brain have specific functions
 Our brains create meaningful experiences from
sensory information
 Brain structure and function is influenced by
experience
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A NEURON is a nerve cell.
There are three basic types of neurons (diagram):
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Sensory Neurons: Afferent neurons that detect stimuli from
sense organs and relay this information TO the brain and/or
spinal cord.
Motor Neurons: Efferent neurons that receive signals from the
brain and/or spinal cord and relay this information to glands
and muscles.
Interneurons: neurons in the brain and spinal cord that
coodinate activity between sensory and motor neurons.
Three Types of Neurons in action!
Glial Cells: provide nutrients to neurons, insulate
neurons, and remove debris when neurons die.
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Intraneural
transmission:
within on neuron
This is an
ELECTRICAL
process
Occurs as a result
of the exchange of
charged particles
called ions
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When more negative ions are inside the neuron than outside
Neuron is not transmitting information
Similar to a compressed spring
The neuron is POLARIZED – meaning it has a charge (-)
System WANTS to reach equilibrium and balance charges, but
selectively permeable membrane is closed when in this state
known as resting potential
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Sudden, massive change in
charge in the neuron
Neuron reaches the
threshold of excitation when
neighboring neurons’
excitatory signals
outnumber inhibitory
signals
Ions flow across cell
membrane down axon
(domino effect) facilitated
by myelin sheath
Na+ in, K+ out
Neuron fires and
DEPOLARIZES – no charge
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A neuron either fires or it
does not
When it does fire, it will
always produce an
impulse of the same
strength
Intensity of a stimulus is
coded by the frequency of
action potentials or the
number of neurons that
fire
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In other words, if there are
several neighboring
neurons firing, or one
neuron firing repeatedly,
the stimulus may be intense
enough for the neuron to
fire.
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Absolute refractory period
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Relative refractory period
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Period immediately after an action potential when
another action potential cannot occur
Period following absolute refractory period when a
neuron will only respond to a stronger than normal
impulse
During the refractory period, the neuron is trying
to get back to resting potential by pumping out
K+ ions!
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Impulse has traveled down the length of the
axon
Signal end up at terminal buttons, very end
points of the axon terminals
Then what?
Signal must get to other neurons, but how?
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The synapse
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Composed of the terminal button of one neuron, the
synaptic space, and the dendrites or cell body of the
receiving neuron
Synaptic space (synaptic cleft)
Tiny gap between neurons
 Messages must travel across the space to get from
one neuron to the next
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Interneural: between
neurons
a CHEMICAL process
Synaptic vesicles
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Sacs in terminal button that
release chemicals into
synaptic space
Neurotransmitters
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Presynaptic
Neuron
Chemicals released by
synaptic vesicles
Receptor sites
Location on receptor
neuron for specific
neurotransmitter
 Lock and key
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Reuptake
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“Recycling”
neurotransmitters
Postsynaptic
Neuron
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Neurotransmitters
regulate many
aspects of behavior
An imbalance of
neurotransmitters
may cause
maladaptive
behavior
Neurotransmitters
may be inhibitory,
excitatory or both
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Drugs’ impact on the body
has helped scientists
discover neurotransmitters,
neuropeptides (e.g. amino
acids such as endorphins)
and neuromodulators that
can increase or decrease the
activity of certain
neurotransmitters
How do drugs work?
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Agonists mimic or prevent
reuptake (1, 3)
Antagonists block
neurotransmission (2)
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Botulism
Blocks release of ACh at
the neuromuscular
junction, causing paralysis
 “Botox” is botulism toxin
used to prevent facial
muscles from making
wrinkles
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Block dopamine receptors
 Reduces schizophrenic
hallucinations
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Curare – found in vines in
S. America; used as poison
Can stun or kill prey
quickly
 Blocks ACh receptors
causing paralysis
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Antipsychotic medications
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Caffeine
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Increases the release of
excitatory neurotransmitters
by blocking the inhibitory
neurotransmitter adenosine
Cocaine
Prevents reuptake of
dopamine
 Leads to heightened arousal
of entire nervous system
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All of our physical
and emotional
reactions are the
product of
communication
between the brain
and the rest of the
body
Endocrine System =
Glands (hormones)
Nervous System =
Neurons
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Our brain is the
“supercomputer” and may
instruct our glands to release
hormones AS IT IS
instructing the neurons in
the central and peripheral
nervous systems to fire
Example: You are being
chased by a bear!
Brain -> Endocrine- Release
adrenaline from adrenal
gland
Brain -> CNS- communicate
via epinephrine (NT) to
excite SNS
I hate being
naked in
front of all
these
students…
Tell
me
about
it!
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Helps coordinate and
integrate complex
psychological reactions
Endocrine glands secrete
hormones into the
bloodstream
Hormones serve to organize
the nervous system and body
Hormones also activate
behavior, such as sexual
behavior, hunger and
aggression
Slower communication than
Nervous System (but impacts
last longer)
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Thyroid gland
Secretes hormones
(primarily thyroxin) that
control metabolism
 Hypothyroidism and
Hyperthyroidism
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Referred to as the “master
gland”
 regulates many other glands
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Reaction to stress
 Secretes adrenaline
(epinephrine)
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Adrenal glands
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Pineal gland
Sleep-wake cycle
 Secretes melatonin
Pituitary gland
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Gonads
Pancreas
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Regulates blood-sugar
levels
 Secretes insulin
 Diabetes?
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Ovaries and testes
secrete estrogens and
androgens
Brain  Pituitary  other glands  hormones  brain
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Afferent and Efferent neurons carry messages
to and from central nervous system to
glands/muscles
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Fight-or-flight
response
Sympathetic:
Arouses
Parasympathetic:
Calms
Central Nervous System
Brain
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Brain
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Spinal Cord
Enables all functioning
Billions of neurons and their connections
These neurons work together in neural networks to
facilitate efficient output.
As we learn, these networks strengthen
Spinal Cord
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Connects brain to PNS
Handles reflexes
I rule.
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Without our brains,
we would really be
nothing!
“The mind is what the
brain does”
Brain + Body = Mind
We live somewhere
“north of the neck”
What would happen
if our brains were
placed into another
human’s body?
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Studying the brain
through lesions or
damaged areas
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“Ta” and Phineas Gage
Experiments in rats –
hypothalamus lesions
Monitoring Electrical
Activity: the EEG
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Electroencephalograms
provide information
about cortical activity
Record electrical activity
of neurons on surface of
brain (neural firing)
A functional technique
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CT Scan (Computerized
tomography)
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Computer-assisted x-ray of
brain
Used to create overall images
of brain
MRI (Magnetic Resonance
Imaging)
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Produces detailed pictures of
soft tissue in brain
Can focus on specific regions
when CT cannot produce
clear images
CT scan
(top) and
MRI
(bottom)
showing a
tumor.
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PET (positron emission
tomography)
Image created by the rate at
which radioactive glucose is
metabolized
 Which areas of the brain are
active during a particular activity
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fMRI (functional MRI)
Combines structural and
functional techniques
 Multiple images of brain created
during a particular task
 Records changes in blood flow to
indicate regions of greater
activity
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Brainstem
Oldest part of brain
Contains medulla, controlling heartbeat,
blood pressure and breathing
 Also contains pons, which helps regulate
sensory information and facial expressions
 Contains Reticular Formation (RF) for
alertness/arousal, sleep/wakefulness
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Thalamus
Pair of egg-shaped structures on top of
brainstem
 Routes all incoming sensory information
except for smell to appropriate areas of brain
 Communicates with higher level of brain
 Penn Station
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Cerebellum
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“little brain” at read of brainstem
Controls coordination, balance, and muscle
tone
These parts of the brain are
our “autopilot” so other
regions can deal with higherlevel “human” functions
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Located in between the primitive parts of the brain
and the cerebral hemispheres
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Hippocampus processes new memories (case of H.M.)
Amygdala controls emotions such as aggression and fear –
in animals, the “attack” response (rat study)
Hypothalamus regulates hunger, thirst, body temperature
and sex drive – also controls pituitary gland
 Rat study – self-stimulation of “pleasure centers”
 Human implications? Mild pleasure, addiction tendencies?
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Primarily, the limbic system processes drives, smell
and various emotional responses
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Part of the cerebrum, the
two large hemispheres
comprising 85% of brain
weight
Wrinkled outer layer
Why so convoluted?
Higher level functions
Designation of cortical
space and “higher level”
animals?
Most highly evolved
part of the human brain
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Each hemisphere
is divided into 4
lobes
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Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
The lobes are
separated by deep
convolutions
known as fissures
Homunculous!
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Occipital Lobes
Parietal Lobes
Visual cortex
Damage?
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Temporal Lobes
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Auditory cortex
Auditory hallucinations?
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Primary sensory or
somatosensory cortex
Allocation of space?
Frontal Lobes
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Most evolved
Motor cortex, which
allows us to move
Allocation of space?
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We only use 10% of our brains?
Undifferentiated cortex
Association areas
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In 1848,
railroad
foreman
Phineas Gage –
accident!
No longer
“himself”
Emotions, the
frontal cortex,
and the
unchecked
limbic system
The skull of Phineas and rogue tamping iron,
displayed proudly at Harvard University’s
medical school! For real!
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Brain’s ability to change
and reorganize as a result
of experience
Mark Rosenzweig’s (19222009) Rat Studies (1950s60s)
Implications for humans?
Shafted
again.
Hey guys! Check out
our phat crib!
Party!
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Recent evidence has
suggested that human
brains may be able to
generate new brain cells,
known as Neurogenesis
Stem cell research?
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Two halves are NOT identical
Most have a dominant hemisphere – usually
the left, which controls the right side of the
body
Both sides serve important functions,
revealed by studying split-brain patients
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Epilepsy, seizures and the
corpus callosum
Reduction in epileptic seizures
Different abilities in each
hemisphere
The story of “Vicki”
Michael Gazzaniga
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Left Hemisphere
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Language in most
people: The cases
of Ta of Charles
Landry
Logic
Right side of body
Right
Hemisphere
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Perception
Sense of self
Inferences
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90% of humans are right-handed
The 10% of left-handers show less predictable
patterns of hemispheric dominance
Causes?
Genetics?
 Fetal testosterone levels?
 Learned?
 Handedness and sexual orientation?
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A closer look: a curse or an advantage?
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Behavior
Genetics seeks to
understand the
relative influence
of our heredity
and our
experiences
Nature vs.
Nurture? It’s both
– but how much
of each?
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Heredity examines the transmission of
trait from one generation to next
Chromosomes
Pairs of thread like bodies that contain
genes
 Average human cell has 23 pairs
 Sex cells?
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Deoxyribonucleic acid (DNA)
Organic molecule arranged in a doublehelix
 Contains the “code of life”
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Genes
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Basic units of inheritance
Segment of DNA
Genome
“map” for an organism’s genetic complete
make-up
 Human Genome Project
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Animal Studies
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Strain Studies
Selection Studies
Human Studies
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Identical Twins
Fraternal Twins
Separated Twins
Adoption Studies
Family studies
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Temperament refers to emotional
reactivity and seems to be set
very early in life
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Thomas and Chess (easy, difficult,
slow-to-warm-up)
Kagan’s “shy child”
Indicates this aspect of behavior
is genetically manipulated
Environment can enhance or
diminish this genetic
predisposition
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Heritability: the extent to which differences
among organisms are caused by genes
Does NOT refer to which percentage of a
trait is determined by genetics in a given
individual!
The more similar and controlled the
environment of the organisms is, the more
we can attribute differences to genes, and
the higher the heritability!
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Genes and environment interact like “two hands
clapping…”
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Environment can trigger genetic “switches”
Our genes can provoke us to seek particular environments
e.g. Eating Disorders
 Genetic predisposition (some are more susceptible than others)
 Cultural regulation (Western culture)
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Molecular Genetics (Behavioral Genetics)
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Studies how particular genes influence behavior
e.g. Is there a gene that determines obesity? Sexual
orientation?
Promise and peril of molecular genetics?
 Genetic engineering- successful in breeding “intelligent” rats
 Eugenics- Blood tests before marriage; prescreening for genetic
disorders
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Whereas behavior geneticists seek to explain
our behavioral differences in terms of our
genes, evolutionary psychologists focus on
our similarities, as dictated by natural
selection.
Richard Dawkins The Selfish Gene (1976)
Varied organisms in a population compete to
survive
 Certain biological and behavioral variations
facilitate survival
 Surviving organisms may reproduce and pass
on their genes
 This leads to overall changing characteristics
in a population
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Selection – providing a reproductive advantage, either
naturally or artificially (e.g. tame foxes), based on a trait/set
of traits
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These traits will endure over time
Population will change as a result
Variation can result from mutations (errors in genetic
replication right after conception)
Some of these “errors” provide an advantage and are selected
for, and therefore persist
 The errors are adaptive – increasing our fitness, or our chances to
survive (and to reproduce)
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Humans have so many shared characteristics – How?
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Differences that were not “fit” were not passed on
Those that increased survival were, as these organisms lived and
reproduced
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Selection happens
SLOWLY and often our
world changes faster than
the gene pool can (e.g.
fatty/sweet food cravings)
Today, evolutionary
psychologists examine
persistent trends in human
behavior and seek to
explain them
Keep in mind, however,
that genetically driven
tendencies only partially
govern human behavior!
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Males of all sexualities
generally are more interested
in sex, regard sex as a
recreational activity and
prefer young, attractive mates
Females of all sexualities
generally see sex as an
outgrowth of relationships
and prefer mature, stable, and
affluent mates
Have these trends genetically
motivated?
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Women
Quality over quantity
More invested in bearing/nurturing
children
 Seek men who either provide superb genes
(he-man strategy) or are good providers
(domestic-bliss strategy)
 “fast” vs. “coy” females
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Men
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Perhaps males
should invest more in
child-rearing?
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Quantity over quality
Increase reproductive success by spreading
their genes as widely as possible
Attraction to fertile females
Not physically bound to pregnancy
He-man strategy vs. opportunists
Philanderers vs. Stable males?
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Do these arguments just
provide excuses for bad
behavior?
Do humans have more of a
social and cultural
responsibility to make the
world better?
What about environmental
influence?
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How does the environment
reinforce these trends?
How much of a role does
environment play in the
persistence of these roles?
Who benefits?
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Experience and Brain Development
Critical Periods – “Use it or lose it”
 Rosenzweig revisited
 Brains are shaped by our genes AND
experience- Lines and colors on a coloring page
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Parental Influence?
If abusive or neglectful, can have major impact
In non-extreme cases, parents probably deserve
less credit, or less blame!
 Parents shape values, beliefs and habits, but
not as much as we may believe
 Most important to provide unconditional love
and support
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Peer Influence
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Peers teach us how to socialize and cooperate
Selection effect: seeking peers with similar
interests
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Culture
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distinctive values, beliefs,
language and characteristics of
a society
both tangible (food, clothing)
and intangible (values, beliefs).
Norms
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Rules that represent the typical
behaviors of a particular group
One example is expected
personal space, the distance
we like to keep ourselves from
other people
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Do you base your self-perception on the traits you possess
(athleticism, looks, intelligence) or on your sense of belonging
(relationship with friends/family)
Do you define success as performance in career or in terms of
the relationships you form and the roles you fulfill.
The most important thing about a marriage is personal
happiness. (T/F)
You see a froshie being teased by a group of girls for the shirt
she’s wearing. The girls don’t think she heard, but you know
she did. Do you step in or mind your own beeswax?
Popularity is based on
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a) quality of friendship
b) amount of friends.
Your behavior (success included) is controlled by who you are
and what you want to do. (T/F)
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Individualist cultures place value of singular person over
that of the group
Collectivist cultures value the group over the individual
Which type of culture does the US have? Why?
Implications?
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Aggression involves an intent to
harm, whether verbal or physical:
males admit to and exhibit more
than females.
Men are and are perceived as more
powerful and engage in
behaviors that exhibit and
perpetuate this power inequity.
Females place greater emphasis
on social connections, choosing
careers that involve social
interaction or require nurturing
roles
Males have more difficulty
admitting they are wrong

Women internalize emotions and
behavior; Men see the source of the
problem as external
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X and Y Chromosomes
Y triggers sex differentiation during
fetal development, causing greater
testosterone production in males
Female infants exposed to elevated
levels of testosterone exhibit “male”
behavioral characteristics


Tom boy!
Males with normal male hormones
but had their sex reassigned at birth
for various reasons often embrace a
male identity, despite efforts to raise
them as females

Gender Roles – expected behaviors for males and
females
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Women as caregivers?
Men as breadwinners?
The Reality? Women now OUTNUMBER men in the
workplace in the US, yet in 87% of families with
children, are still the primary caregivers.
Variations across culture and time…
 Gender Identity – our sense of being male or female
 Gender typing – embracing a traditional masculine/feminine role
 Social Learning Theory and Gender Schemas
 Close contact, imitation of superiors
 Learn about what it means to be male/female from culture
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What do these roles and stereotypes provide for us?
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Sense of stability and simplification
Sense of confinement
 Fluidity of gender?
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Our genes and our experiences form us
Family, friends, and culture have an influence
over the genes that make us
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These structures are constantly in flux
We are adaptive creatures
The world changes, and we change with it