Cerebral Cortex

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Cerebral Cortex

• Objectives
• Describe cortical histology
• Review the primary cortical areas
• Differentiate between primary and association
  cortical areas
• Illustrate the functions of association cortex
  with results of characteristic lesions in each
  lobe.

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Cortex laminated gray matter covering of brain
MRI (T1weighted) Gray matter cells White
matter axons
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Cortex Histology Layers of cells

• neocortex 6 layers (90 of human cortex)
• allocortex arcHicortex paleOcortex, 3 layers

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Cortical cell types I. Pyramidal cells

• spiny dendrites
• output cells
• axons make up
• white matter
• One named example is the Betz cell of the motor
  cortex.

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Pyramidal cell axons make up white matter bundles
e.g. arcuate fasciculus
e.g. internal capsule
e.g. corpus callosum and anterior commissure
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Arcuate fasciculus- example of an association
bundle in cortex
Arcuate fasciculus interconnects Brocas and
Wernickes areas
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Cortical cell types II. Nonpyramidal cells

• Spiny or non-spiny interneurons
• Relay information locally

Non-pyramidal aka granule cells, e.g. stellate,
basket, chandelier cells
pyramidal
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Cortical Areas Brodmans crazy quilt
1,2,3-S1
4-M1
17-vis
41-aud
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Layers organize inputs and outputs
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Summary Cortical Histology

• Cortex structural pattern is similar all over
  pyramidal and non-pyramidal cells organized in
  layers and radial modules
• Different areas distinguished by variations on
  the theme different densities and packing of
  pyramidal and non-pyramidal cells

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Functional Localization

• In spite of structural similarity, we know that
  there is functional localization/ specialization
• Primary sensory areas process different input
  modalities
• Primary motor cortex provides specialized output
  for control of muscles
• Specialized language areas exist in the left
  hemisphere

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Functional localization seen in PET scans
Count silently
Speak aloud
Read aloud
Read silently
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Exercise

• Pick one cortical area somatosensory, motor,
  auditory, visual.
• Describe its location, topography, thalamic input
  and part of internal capsule it travels in,
  outputs, function, effects of lesion on one side,
  blood supply.

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Primary Cortical Areas
primary somato- sensory
primary motor
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Primary cortical areas and 3 others
primary somatosensory
primary motor
premotor (and SMA on medial side)
primary visual
Brocas motor language
primary auditory
Wernickes sensory language
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Association Cortical Areas
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Cells in association cortex have complex stimuli
sensitivity

• Large receptive fields convergence
• Uni- or multi-modal responses
• Selectivity for complex stimuli
• No motor responses
• Damage causes deficits in perception, learning or
  memory, adaptive behavior

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Prefrontal association cortex

• Two regions
• dorsolateral strategic planning for higher motor
  and cognitive behavior, working memory
• orbitofrontal emotional responsiveness,
  personality
• Input from mediodorsal nucleus of thalamus and
  high levels dopamine from VTA
• Role in restraint, initiative, order (RIO)

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Prefrontal association cortex
Phineas Gage self-induced frontal lobotomy
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Prefrontal association cortex
LURIA
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Prefrontal association cortex
Wisconsin Card Sort Test (WCST)
Sort by color
Sort by shape
Sort by number
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Prefrontal association cortex

• Lesion in prefrontal cortex
• Cognitive deficits, problems with working
  memory
• Strategic planning, judgment deficits
• Personality/emotional changes
• (damage has some lateralized aspects)

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Temporal association cortex

• Verbal memory (left)
• Patterns of stimuli, musical discrimination
  (right)
• Object recognition (higher order visual
  processing)
• Face recognition (bilateral)

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Temporal association cortex

• Lesion in temporal association cortex
• Verbal memory problems
• Visual discrimination problems
• e.g. prosopagnosia inability to recognize and
  identify faces

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Parietal association cortex

• Higher sensory function (polysensory)
• Language function (especially inferiorly)
• Stereognosis
• Spatial relations, including extrapersonal space
  and body image

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Parietal association cortex

• Damage on right contralateral neglect

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Attentional mechanisms hemispheric asymmetry
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Occipitalassociation cortex

• Higher order visual perception

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Occipitalassociation cortex
Lesion of occipital association cortex
visual agnosias
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Summary Association Cortex

• Important for higher order function, cognition
  and memory storage
• Regional specialization of association cortex
• In parietal lobe-for attention to complex stimuli
  from environment and to internal motivation
• In temporal lobe for identification, recognition
  of complex stimuli
• In frontal lobe for planning appropriate response
  to complex stimuli
• Involved in constructing a unified percept of
  aspects of the world.

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Language areas left and right

• Language function usually on left
• Brocas
• Wernickes
• Lesions cause aphasias
• Equivalent areas on right have some role in
  language also in prosody and its perception.

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Split-brain studies reveal laterality in cortex
function
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Lateralization of function in the cerebral
hemispheres
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Summary

• Cortex is cool and complicated
• and deserves way more attention than we give it.