HMB200H1 Lecture Notes - Lecture 19: Arcuate Fasciculus, Parahippocampal Gyrus, Visual Cortex
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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.
• 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
• 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
• 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
o A1 has connection w speech
• Green = Limbic
o Old, thin
o Cingulate gyrus, parahippocampal gyrus, temporal pole, into
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
• 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 MEANINGLESS SPEECH
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
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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