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 species differ in the relative sizes of 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 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
 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)
4.
Motor nerves exit the spinal cord, excite the muscle, and initiate a movement
3.
Interneurons excite motor neurons in the ventral gray portion of the spinal cord

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
 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
Microelectrode
Extracellular Fluid
Membrane
Intracellular Fluid

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