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Lecture 19

HMB200H1 Lecture Notes - Lecture 19: Arcuate Fasciculus, Parahippocampal Gyrus, Visual Cortex

Human Biology
Course Code
John Yeomans

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HMB200H1S L19; March. 20, 2012
Cortex: From Limbic to Association
Cortex go from 3 layers to 6 layers, very difficult to DEFINE.
How it evolved from limbic cortex to association cortex!
Evolution of Cerebral Cortex how layers have evolved
Subcortex: e.g. basal ganglia, extended amygdala.
Paleocortex: e.g. basal forebrain, olfactory.
Archicortex & transitional: e.g. medial prefrontal, insular,
Limbic cortex: orbitofrontal, cingulate, parahippocampal.
Primary neocortex: Motor, somatosensory, visual, auditory.
Association neocortex: Frontal, Parietal, Temporal.
Cortex Types
Layers of neocortex
Paleocortex: 0.5mm thick, 3 layers
Association: gets a lot of cortical input, outer layers = thicker, primary
cortices inner layers = thinner?
Transitional: includes hippocampus (evolved from paleocortex,
slightly thicker), orbitofrontal cortex which evolves to primary cortex
Primary: difficult for anatomists to find these layers
o Can see layers III & IV dominant here since receiving direct
thalamic visual & auditory input
o 2mm thick?
Cerebellar cortex: 3 layers
Anatomical Definitions
Oldest dortex = Basal Forebrain Colonoergic 0.5mm, thinnest cortex
Paleocortex: 3 layers
o Gradual transition to 6 layers as layers added on over long time
Transitional cortex: 36 layers.
o Hippocampus = highly developed, has 3 or 4 layers
Limbic: Visceral inputs (taste, olfaction, hypothalamus, dopamine).
Primary neocortex: Somatic inputs from thalamus.
o Layers 4 & 5 dominate.
o Evolved from hippocampal to 6 layers
Association neocortex: Cortical and non-primary thalamus inputs
(mediodorsal n, pulvinar)
Brodmann’s Areas (1-42)
Distribution of functional zones in relation to Brodmann’s map of
human cortex
Start w motor cortex to frontal pole. then started in center again &
went to posterior area
Mammalian brain has large Neocortex recently discovered
o Sometimes called Isocortex only found in mammals, not birds
o 2mm thick
Blue = Primary Cortical Areas
o After primary is higher order assn cortex = combo of senses
working together
o A1 has connection w speech
Green = Limbic
o Old, thin
o Cingulate gyrus, parahippocampal gyrus, temporal pole, into
frontal cortex
o Pyriform cortex = Olfactory cortex
Other sensory cortex like visual & somatosensory
Evolution: Green Blue Yellow Pink
o Limbic Primary Unimodal assn Higher assn
HMB200H1S L20; March. 21, 2012
Speech and Language
Bird Song and Left Hemisphere
Go thru neurogenesis in spring, degredation in winter
Testosterone helps regeneration in left hemisphere sing differently
each summer for male courtship calls
Growth only on left side of brain lateral f’n
o idea that speech is lateralized in left hemisphere
Human Aphasias
97% have left hemisphere injury.
o Injury to Broca’s Area = Broca’s Aphasia
o 3% right hemisphere injury

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Broca’s Tan. “No ifs, ands, or buts”
Wernicke’s Aphasia. Lots of meaningless words.
o Poor understanding, and recovery.
o Fluent speech but poor comprehension
Wernicke’s Theory of Speech and Reading.
Werkicke-Gershwind model:
o Sound reaches ear auditory system processes the sounds
neaural signals reach auditory cortes
o Sounds don’t become words unless identified by Werknicke’s
o To repeat the words: Word-based signals sent from Wernicke’s
to Broca’s via Arcuate Fasciculus muscular movement for
speech (go to motor cortex)
o Visual info can reach Broca’s w/o going thru angular gyrus
Broca`s Aphasia:
o Can produce words w HIGH MEANING & poor grammar
o Speaking very gradually
o Writing is NOT consistent
o Lack Flow within sentences
o Can't say many words
o = PRODUCTION APHASIA inability to produce words.
Temporal Lobe damage includes Wernicke`s Area
o Speech problems
o Don't understand speech well
o Damage to auditory association cortex in temporal lobe, includes
ventral parietal lobe.
o Able to speak perfectly
o Can easily say "No, ifs, ands and buts!"
Human Speech and Left Hemisphere
Understand the first 4 types
Conduction aphasia:
o Damage btwn the area, like the Arcuate area
o Repeat slowly
Paraphasia: using the wrong words
Working Model of Speech Organized Within Brain
Damage to Arcuate fasciculus Conduction aphasia
o Hard to repeat speech
Output from Arcuate fasciculus, arching around Sylvian fissure
Broca’s – speech info processed
Broca’s – organizes speech patterns
Both B & W lesioned many losses within brain
o Global Aphasia
Learn language from mothers, presented in auditory mode
Info comes from Primary Auditory cortex W B via Arcuate
produce fully competent speech activates Motor Cortex for speech
to occur
Working Model of Written Words
Auditory area in Lateral Temporal lobe
Angular gyrus back of Superior Temporal lobe
Primary visual cortex info Angular Gyrus translates into auditory
info W speech production
Anatomical Changes (btwn right & left hemispheres)
Auditory association cortex looks dif in each hemisphere
Planum temporale is larger in the left hemisphere of most people.
Some dyslexics show disruption of neurons in left angular gyrus,
or planum temporale.
o Found disruption in cells, layers of cortex are NOT formed
Galaburda, Geschwind
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