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Chapter 13

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University of Toronto St. George
Zachariah Campbell

Anatomy of the Occipital LobesThe occipital lobes form the posterior pole of the cerebral hemispheres lying beneath the occipital bone at the back of the skull On the medial surface of each hemisphere the occipital lobe is distinguished from the parietal lobe by the parietal occipital sulcusThere are no clear distinctions of the occipital cortex from the temporal and perietal cortex oespecially on ventral surface where the OC extends to merge with PC and TCWithin the visual cortex are three clear landmarkso most prominent is the calcarine sulcus which contains much of the primary cortex divides the upper and lower halves of the visual world oOn the ventral surface of each H are two gyri lingual gyrus part of visual cortical regions V2 and VPfusiform gyrus V4 A Subdivisions of the occipital cortexV4V8 color some areas contain complete visual field some have only upper or lowerupper visual search functionslower visuomotor guidanceV1 has complex laminar organizationarea 4 of the cortex layers here split into many more layersanatomically heterogeneousregions of cytochrome rich areas blobs for color perception separated by regions with little cytochrome activity interblobs for form and motion perception oV1 is also functionally heterogeneous that a given cortical area may have more than one distinct function Area V2 also is heterogeneous when stained with cytochrome oxidase but instead of blobs stripes are revealed ovisual cortex is sometimes called the striate cortexothin stripes color perceptionothick stripes form perceptionopale stripes motion perceptionThe distribution of color function across much of the occipital cortex and beyondthat is areas V1 V2 V4 V8 is important because the perception of form or movement was believed to be color blind It has onow clear that color vision is integral to the analysis ojf position depth motion and the structure of objects relative amount of color processing varies across occipital regions with V4 being major areaB Connections of the visual cortex visual cortex has distributed hierarchical processesomultiple parallel and interconnecting pathways at each levelprinciples of visual connectionsoV1 the striate cortex is the primary visual area receives the largest input from the lateral geniculate nucleus of the thalamusprojects to all other occipital regions first processing level in the hierarchyoV2 also projects to all other occipital regions second level oAfter V2 three distinct parallel pathways emerge en route to the parietal cortex superior temporal sulcus STS and inferior temporal cortex for further processingThe parietal pathway dorsal stream has a role in the visual guidance of movement the inferior temporal pathway ventral stream is concerned with object perception including color The middle pathway along the superior temporal sulcus the STS stream important in visuospatial functions and in the perception of certain types of movementsTheory of Occipital Lobe FunctionV1 and V2 serve as mailboxes into which different types of information are assembled before being sent on to the more specialized visual areasfrom V1 and V1 flow 3 distinct parallel pathwaysoinfo from V1 blobs V4 color area oother info from V1 V2 V3middle temporal for motion detecting
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