The Brain and Behavior Outline Functions Evolution: structure and behavior Basic Unit: The Neuron...

The Brain and BehaviorOutline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses: What does the signal do?• Reflexes: A model• Brain Organizing Principles and Functions

Functions

• Communication• Coordination• Control• Cognition• Complexity

Outline: Start With A Mechanistic View

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses: What does the signal do?• Reflexes: A model• Brain Organizing Principles and Functions

Evolution

• None• Nerve net• Segmented• Cephalization: an organizing principle (brain-

mind correlation not always obvious!)• Kineses• Taxes• Reflexes

Evolution

Brain Structure

Brain Structure

Brain Structure

DRUGS

Evolution

• None• Nerve net• Segmented• Cephalization: organizing principle + brain-function rel.• Kineses• Taxes• Reflexes

Reflexes

• Kinesis (potato bug)

• Taxis (moth / maggot / fly / tick)

• Reflex: (knee jerk)– Descartes 161 St. Germaine on the Seine– Pineal– Mechanist

Reflexes

• Braightenberg: Vehicles

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

The Neuron

• 100 billion

• Varied in size, shape, function

• Function of neuron sending signals in real time (ex.)

• What is the signal? - electrical / chemical

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

Origin of nerve signal

• Function of neuron sending signals in real time (ex.)

• What is the signal? - electrical / chemical

Generation

• Two forces:– Electrical (ionic)– Chemical (concentration)– Give rise to steady-state voltage “resting

potential”– Universal in cells

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

Action Potential

Movement of a Signal

Action Potential

• Cell actions

• Speed: Muller (light), Helmholtz (43 m/sec)

• Refractoriness

• All or none law

• Coding of intensity: analog-digital + recruitment (organizing principle)

Neuron Communication

• Propagation is much faster if the axon is myelinated:• Depolarization proceeds down the axon by a

number of skips or jumps.

• The action potential obeys the all-or-none law:• Once it’s launched, further increases in

stimulus intensity have no effect on its magnitude.

Neuron Communication• Propagation is much faster if the axon is

myelinated:• Depolarization proceeds down the axon by

a number of skips or jumps.

• The action potential obeys the all-or-none law:• Once it’s launched, further increases in

stimulus intensity have no effect on its magnitude.

• Frequency signals intensity

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

Synapses: What happens when signal reaches end of neuron?

• Two types of actions - excitatory / inhibitory

• Chemical model with multiple & functionally different neurotransmitters

• Temporal & spatial summation

Synapses

Release of Neurotransmitter

Synapses

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

A Model for building behavior out of simple building blocks

• Reflexes

• Voting behavior

• Mirror neurons

• Other examples to follow

Reflexes: A model

Outline

• Functions• Evolution: structure and behavior• Basic Unit: The Neuron• Generation: How does a signal get started?• Action Potential: How does a signal move?• Synapses• Reflexes: A model• Brain Organizing Principles and Functions

Principles and Functions

• Cephalization• All-or-None Law• Frequency Coding of Intensity• Doctrine of Specific Nerve Energies• Localization of Function (+ Integration)• Topographic Projection (& Distortion)• Split Brain (Crossed Connections)• Connectivity & Functional Connectivity• Neuro-plasticity & Reorganization

Brain Structure (midline)

Structure: Central Core

Structure: X-Ray View

Localization of Function

• Different parts of the brain serve specialized functions

• Sensory Information

• Motor Control

• Perception

• Language

• Planning and Social Cognition

Localization of Function

Localization/Topographic Projection

Localization/Topographic Proj.

Localization/Topographic Proj.

Cerebral Cortex

• Most projection areas have contralateral organization:

– Left hemisphere receives information from right side of body (sensory), or controls right side of body (motor)

– Right hemisphere receives information from left side of body (sensory), or controls left side of body (motor)

Split Brain

Split Brain

Cortical Damage

• Much of what we know about the cortex comes from studying brain damage.

• Damage at identifiable sites can produce:

• Apraxias (disorders in action)

• Agnosias (disorders in perception)

• Aphasias (disorders of language)

• Disorders of planning or social cognition

Apraxias

• Difficulty in carrying out purposeful movements without the loss of muscle strength or coordination– Disconnection between primary and non-

primary motor areas– Able to carry out each part of a complex

movement, but disruption lies in coordination of the movements

Agnosias

• Visual agnosia: disturbance in recognizing visual stimuli despite the ability to see and describe them

• Prosopagnosia: inability to recognize faces (fusiform face area)– http://www.youtube.com/watch?v=vwCrxomPbtY&feature=related – http://www.youtube.com/watch?v=VKa-PuJCrO4&feature=related

• Neglect Syndrome: complete inattentiveness to stimuli on one side of the body– http://www.youtube.com/watch?v=ADchGO-0kGo&feature=related

• Akinetopsia: inability to perceive movement– “I see the world in snapshots – like frames of a move but most of

the frames are missing”

Aphasias

• Broca’s Aphasia: disturbance in speech production, caused by damage to Broca’s area– http://www.youtube.com/watch?v=f2IiMEbMnPM

• Agrammaticism• Anomia• Difficulty with articulation

• Wernicke’s Aphasia: disturbance in speech comprehension, caused by damage to Wernicke’s area– http://www.youtube.com/watch?v=aVhYN7NTIKU&feature=rel

ated

• Disruption in recognition of spoken words• Disruption in comprehension of the meaning of words• Inability to convert thought into words

Disorders of Planning and Social Cognition

• Caused by damage to prefrontal area– Disrupts executive control– processes that

allow us to direct our own cognitive activities

• e.g., setting priorities, planning, strategizing, ignoring distractors

Plasticity

• The brain is plastic—subject to alteration in the way it functions, such as:

• Changes in the brain’s overall architecture

• The central nervous system can grow new neurons:

• But appears unable to do so with cortical injury

• This promotes stability in the brain’s connections but is an obstacle to recovery from brain damage.

Plasticity

• Neurons are subject to alteration in the way they function, such as:

• Changes in how much neurotransmitter a presynaptic neuron releases

• Changes in neuron sensitivity to neurotransmitters

• Creating new connections by growing new dendritic spines