The horizontal organization of stellate cell dendrites in layer IV of the visual cortex of tree shrews

Abstract

Within layer IV of the visual cortex (area 17) of the tree shrew essentially all of the neurons are stellate cells. The majority (approximately 90%) are small and have spiny dendrites while the rest are larger with smooth dendrites. The dendritic arbors are all confined within the borders of layer IV and show a remarkable tendency, particularly marked for the small cells, to be flattened in a plane parallel to the pia. The dendritic arbors can be regarded as discs. More than half of the arbors occupy less than one-sixth of the thickness of layer IV: about 90% occupy less than one-third of the thickness. The highly oriented arrangement of the dendritic arbors is related to the laminar organization of the geniculocortical terminals in layer IV. It appears that most of the stellate cells can receive their direct input from only one or two of the six geniculate layers. Therefore, interactions between the several retino-geniculo-cortical pathways must occur at intracortical levels.