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Chapter 4
Brain and Behavior
Brain and Behavior
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Adaptive behavior is accomplished
through the action of adapted brains
The case of Phineas Gage
– Damage to area at the front of the brain
results in loss of planning abilities and
“civilized behavior”
The Origins of the Human Brain
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Brain size
correlates with
body size
– Big animals
have big brains
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Brain/body ratio
distinguishes
apes from most
other animals
Similarities to other animals
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All animals have the following
organization of brain structures:
– Hindbrain
– Midbrain
– Forebrain
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Different species
differ in the
relative sizes
of these areas
Cerebral Cortex
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Cerebrum evolved relatively recently
Much more prominent in mammals
– Corticalization
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Results in and “enormous elaboration of
powers” (Dennett, 1995).
Organization of the Brain
The “Vertebrate Plan”
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All vertebrates have a similar brain
organization
The Human Nervous System
The Human Nervous System
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Central Nervous System (CNS)
– Brain and Spinal Cord
The Human Nervous System
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Peripheral Nervous System (PNS)
– Carry information to and from skin, organs
in body, etc
– Subdivided into:
• Somatic Nervous System
– Sensory & motor nerves to periphery
• Autonomic Nervous System
– Sympathetic/Parasympathetic Divisions
Sympathetic and Parasympathetic Divisions
of the ANS
Continued on next slide
Sympathetic and Parasympathetic Divisions
of the ANS
Neurons

Basic functional unit of the nervous system
The Synapse
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Connection between neurons
Small gap between the axon terminals
of one neuron and the dendrites of the
next
Communication between neurons
results from the secretion of
neurotransmitters
Sensory Motor Reflex

Behavior occurs solely as the result of
activity at the spinal cord
2. Sensory neurons
excite interneurons in
the dorsal gray portion
of the spinal cord
1. Flame stimulates
pain receptors
(sensory neurons)
3. Interneurons excite
motor neurons in the
ventral gray portion
of the spinal cord
4. Motor nerves exit
the spinal cord, excite
the muscle, and
initiate a movement
Organization of the Spinal Cord
Brain and Behavior

The Reticular Formation
– Responds to arousing stimulation
Brain and Behavior

Thalamus and Somatosensory Cortex
– Homunculus
(“little man”)
– Representation
of body
on thalamus and
somatosensory
cortex
Homunculus

The greater the number of nerves in a
body area, the larger its brain
representation
– Fingers or mouth vs. back or arm
Organization of the Cerebral Cortex
The Human Cortex

The human cortex is much larger
relative to other brain areas than is the
case for other animals
The Human Cortex
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Primary Sensory Areas
– Areas that receive sensory information

Association Areas
– Areas that make connections between
senses

Humans have much more association
areas than primary sensory areas
Studying Brain Damage
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Accidents
Effects of Strokes
Damage influences behavior on side of
the body opposite to damaged side of
the brain
Neurogenesis

The formation of new neurons
– Recent evidence suggests that adult
humans can form new neurons
The Cerebellum

Responsible for
– Coordinated motor activity
– The development of conditioned
associations
Two Cerebral Hemispheres
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Lateralization of Function
– Left and right hemispheres of cerebral
cortex do different things
Lateralization of Function
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Dichotic Listening Test
– Present words through headphones to left
and right ears simultaneously
– Most people will report hearing the words
presented in the right ear
– Indicates the left side of the brain
processes language
Lateralization of Function
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PET Scans
– Positron-emission tomography
– Indicates brain activity using a radioactive
form of glucose
• Greater activity results in greater glucose
usage
– Language tasks increase activity in the left
hemisphere
The Split Brain Procedure
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The Corpus Callosum
– Set of fibers connecting the two
hemispheres
– Epileptic activity can travel across the
corpus callosum
The Split Brain Procedure
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Cutting the corpus callosum reduces
severity of epileptic seizures
Results in the two hemispheres being
functionally separated
Testing Split Brain Patients
Testing Split Brain Patients
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Only left hemisphere can respond
verbally
– Right hemisphere can use motor
responses (e.g. pick up an object with the
left hand
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Seeing with and without awareness
– Right hemisphere cannot communicate its
awareness
Right Hemisphere
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Emotions
Artistic ability
Spatial ability
Musical ability
Neurotransmitters and Drugs
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Resting Potential
Inside of neuron is negatively charged
relative to the outside
– More negatively charged chemicals inside
than outside
The Resting Potential
Microelectrode
Extracellular Fluid
Membrane
Intracellular Fluid
Neurotramsitter Activity
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Neurotransmitter activates receptors on
postsynaptic cell
– May result in depolarization of cell
• Cell’s charge becomes less negative
• Excitatory Post-Synaptic Potential (EPSP)
– May result in hyperpolarization of cell
• Cell’s charge becomes more negative
• Inhibitory Post-Synaptic Potential (IPSP)
Action Potentials
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Neuron adds together EPSPs and
IPSPs
– If membrane is depolarized sufficiently it
will generate a sudden change in the
electrical state of the cell
• Action Potential
Ion Channels and Action
Potentials
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Depolarization of the neuron results in
the opening of sodium (Na+) ion
channels
– Na+ flows into cell, making it much more
positively charged
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Potassium (K+) then flows out, making
the cell much more negative
All or None Principle
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Action potential is a complete nerve
impulse
Travels down the axon at the same
strength
Cannot be degraded
Saltatory Conduction
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Myelin globules are divided by Nodes of
Ranvier
Action potential can “leap” from one
node to the next
– Increases the speed of the action potential
100-fold
Neurotransmitter Release
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Neurotransmitters stored in axon
terminal in vesicles
Action potential arrives at axon
terminals
– Causes Calcium (Ca++) influx
– Results in vesicles moving to wall of axon
terminal and releasing neurotransmitter
Neurotransmitters
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Multiple Neurotransmitters
“Lock and Key” model
– Each neurotransmitter chemical can only
attach with one type of receptor
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Different neurotransmitters have
different effects
Drugs
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Many drugs influence neurotransmitter
activity
– Reduce re-uptake
• Cocaine
– Block receptor
• Curare
– Mimic neurotransmitter
• Morphine