Chapter 4
Brain and Behavior
Brain and Behavior
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
Brain size correlates with body size– Big animals
have big brains Brain/body ratio
distinguishes apes from most other animals
Similarities to other animals All animals have the following
organization of brain structures:– Hindbrain– Midbrain– Forebrain
Different speciesdiffer in therelative sizesof these areas
Cerebral Cortex
Cerebrum evolved relatively recently Much more prominent in mammals
– Corticalization Results in and “enormous elaboration of
powers” (Dennett, 1995).
Organization of the Brain
The “Vertebrate Plan” All vertebrates have a similar brain
organization
The Human Nervous System
The Human Nervous System
Central Nervous System (CNS)– Brain and Spinal Cord
The Human Nervous System
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 Divisionsof the ANS
Continued on next slide
Sympathetic and Parasympathetic Divisionsof the ANS
Neurons Basic functional unit of the nervous system
The Synapse
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
1. Flame stimulates pain receptors (sensory neurons)
2. Sensory neurons excite interneurons in the dorsal gray portion of the spinal cord
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”)
– Representationof bodyon thalamus andsomatosensorycortex
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
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
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
Lateralization of Function– Left and right hemispheres of cerebral
cortex do different things
Lateralization of Function
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
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 The Corpus Callosum
– Set of fibers connecting the two hemispheres
– Epileptic activity can travel across the corpus callosum
The Split Brain Procedure
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
Only left hemisphere can respond verbally– Right hemisphere can use motor
responses (e.g. pick up an object with the left hand
Seeing with and without awareness– Right hemisphere cannot communicate its
awareness
Right Hemisphere
Emotions Artistic ability Spatial ability Musical ability
Neurotransmitters and Drugs
Resting Potential Inside of neuron is negatively charged
relative to the outside– More negatively charged chemicals inside
than outside
The Resting Potential
Extracellular Fluid
Intracellular Fluid
Microelectrode
Membrane
Neurotramsitter Activity
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
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 Depolarization of the neuron results in
the opening of sodium (Na+) ion channels– Na+ flows into cell, making it much more
positively charged Potassium (K+) then flows out, making
the cell much more negative
All or None Principle
Action potential is a complete nerve impulse
Travels down the axon at the same strength
Cannot be degraded
Saltatory Conduction
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
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
Multiple Neurotransmitters “Lock and Key” model
– Each neurotransmitter chemical can only attach with one type of receptor
Different neurotransmitters have different effects
Drugs
Many drugs influence neurotransmitter activity– Reduce re-uptake
• Cocaine
– Block receptor• Curare
– Mimic neurotransmitter• Morphine