The Brain

Lecture Overview

• Methods of Studying the Brain

• Structure of the Brain

• Localization of Function

• Brain Lateralization

• Plasticity

Studying the Brain

• Study Brain Damage– Animal Studies– Cases of Human Brain Damage– TMS

• Recording the Brain– EEG– Neuroimaging

Brain Damage

• In some animal studies, damage is produced in the laboratory.

• But neuropsychologists often study naturally occurring cases of brain damage.

• Transcranial magnetic stimulation (TMS):

• Scientists can use TMS to study the effects of temporary brain damage.

Recording the Brain

• Techniques are used to study the whole brain:

• Electroencephalography

• Uses sensitive electrodes on the scalp to measure voltages produced by brain activity

• Neuroimaging

• CT, MRI, fMRI, PET scans

Recording the Brain

• MRI and CT scans

• Study the brain’s anatomy—the size and location of individual structures

• PET and fMRI scans

• Reveal which brain locations are particularly active at any moment in time

Recording the Brain

• All these techniques make it clear that most activities rely on many brain sites.

• Activities like reading or making decisions are supported by coordinated functioning of many different parts of brain.

Brain Anatomy

Brain Structure

• The very top of the spinal cord forms the brain stem.

• It includes the medulla and the pons.

• Just behind these is the cerebellum.

• The midbrain is on top of the pons, and on top of them all is the forebrain.

The Cortex

• The outer surface of forebrain is the cerebral cortex.

• The cortex is a large, thin sheet of tissue crumpled inside the skull.

• Some of the convolutions divide the brain into sections:

• The frontal lobes, the parietal lobes, the occipital lobes, and the temporal lobes

Left and Right Hemispheres

• The brain is symmetrical around the midline.

• Most structures come in pairs:

• One on the left side

• One on the right side

Localization of Function

• Different parts of the brain serve specialized functions

• Sensory Information

• Motor Control

• Perception

• Language

• Planning and Social Cognition

Cerebral Cortex

• Some parts serve as projection areas:

• The first receiving stations for information coming from the sense organs (e.g., somatosensory projection areas)

• Departure points for signals going to the muscles (e.g., motor projection area)

Cerebral Cortex

• Adjacent sites in the brains usually represent adjacent parts of the body.

• Assignment of space is disproportionate:

• Usually the parts of the body that are most sensitive to touch receive the most space (in somatosensory projection area).

• Parts of the body that we can move with more precision receive the most space (in primary motor projection area)

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)

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=related • 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

Lateralization

• The left and right hemispheres are generally similar

• However, the two hemispheres have specialized capacities

– Left hemisphere: language

– Right Hemisphere: visual and spatial tasks

• The two halves of the brain work as an integrated whole

– Communicate with each another through commissures

• Split Brain Patients

Other Split Brain Experiments

http://www.youtube.com/watch?v=ZMLzP1VCANo

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