Sensory Association Cortex PDF

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Association cortex = sensory inputs to motor response Unimodal association cortices Somatosensory, visual, auditory Primary cortex  Unimodal association cortex  Poly/Supramodal association cortex Raw information  Some  Planning motor output via primary motor cortex Cerebral artery distributions ACA MCA PCA Multistage Hierarchical Processing Different types of analyses are performed in parallel (e.g. size/shape and location/movt.) Perception depends on the resulting distributed representation Case 1 – Apperceptive visual agnosia Cannot point to named objects or name objects Normal visual acuity Names object via touch - Visual acuity in the primary visual cortex - Loss of higher order visual processing via unimodal assoc cortex (loss of object recog) - Touch perception normal, lesion doesn’t involve somatosensory cortex Case 2 – Loss of color vision Loss of color visual, otherwise normal visual function Likely to be PCA infarct Selective damage tells us this is parallel to association cortex Case 3 – Loss of form vision w/ preserved movement vision Accurately points to objects but cannot name them or describe purpose/function (Apperceptive visual agnosia) PCA damage? Severe damage to unimodal visual assoc cortex, sparing dorsal aspect Visual unimodal association processing (PCA) Occipitotemporal = “What” Occipitoparietal = “Where”

Language is localized to the supramodal cortex in the perisylvian region of L hemisphere Phoneme is a fundamental symbolic unit Broca’s area = motor / speech output = area 44/45 Wernicke’s area = sensory / language comprehension = area 22 Arcuate fasciculus links Broca and Wernicke’s areas (bidirectionally) AF is a part of the superior longitudinal fasciculus Case 4 – Broca’s aphasia Left hemisphere stroke that damages frontal lobe including Broca’s and (pre-)motor cortex Unable to produce much language, rather produces labored and slurred speech (dysarthric) Able to follow verbal and written instructions - Comprehension is intact - Repetition is impaired - Cortex for oral motor representation of phonemes damaged = dysarthric speech - Comprehension is intact bc Wernicke’s area is still intact - Brocas is actually located in the insula Case 5 – Conduction aphasia Infarct to area 22 Good comprehension of written and spoken language, decent speech Spontaneous language full of repeats and phonemic substitutions - Non-dysarthric speech, fluent - Phonemic paraphasias (substitutions) - intact comprehension - Impaired repetition - entire perisylvian language cortex used to convert words into speech, both areas intact Case 6 – Transcortical sensory aphasia - non-dysarthric speech - difficulty finding words - semantic paraphasic errors (uses wrong words) - impaired comprehension - repetition is unimpaired (because Broca’s/Wernicke’s are spared) - isolation of perisylvian cortex = generation and comprehension of speech impaired

Wernicke’s aphasia = transcortical sensory aphasia + conduction aphasia Fluent, non-dysarthric speech Semantic paraphasic errors Impaired comprehension Impaired repetition Apraxia = inability to carry out specific actions on command, eg use tools. Ventral visual association cortex (“what”) = used to recognize tool Left perisylvian cortex = used to name the tool Dorsal visual association cortex (“where”) = mind’s eye image of tool movement Premotor cortex = mind’s hand and arm of using the tool (this almost always opposite in terms of hemisphere to dominant hand) Ideomotor apraxia...