Association and intrinsic connections of human extrastriate visual cortex.

Human extrastriate visual cortex contains several functionally defined visual areas of which four (V2, VP, V4 and V5) can be identified using cyto- and myeloarchitectonic criteria. A case with a small lesion in the superolateral part of cytoarchitectonic area 19, outside the previously defined visual areas, has been studied with the Nauta method for anterogradely degenerating axons. The infarcted part of cortex formed dense intrahemispheric connections in some visual areas (V1, V2, V3 and probably a part of V4) and weaker connections in others (VP, V5). Connections to V1 and to V2 were mainly directed to the representation of the lower paramedian part of the visual field. Intrinsic connections, visualized by the degenerating axon segments in the cortex around the lesion, had a patchy distribution. In conclusion, intrahemispheric corticocortical connections link preferentially some of the visual areas and within these areas certain parts.