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