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Transcript
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 nonprimary 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=relate
d
• 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=ZMLzP1VCA
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