The geniculostriate projection in the grey squirrel: preliminary autoradiographic data

Anterograde autoradiographic experiments reveal connectional specificity between the dorsal lateral geniculate (LGN) laminae and striate cortical layers in a rodent, the gray squirrel (Sciurus carolinensis). Our data indicate that although the geniculostriate projection does not segregate right and left eye information within layer IV, geniculate projections to this layer are tightly organized such that particular cortical substrata receive input from specific LGN layer(s). Preliminary data suggest that geniculate layers 1 and 2 of the LGN project to a central zone of layer IV. In contrast, the layer 3 complex projects densely to a dorsal and ventral tier in layer IV, as well as to layer VI and the supragranular laminae. It is speculated that the input to supragranular layers arises from cells within layer 3c. which in turn, have been shown to receive input from the stratum griseum superficiale of the superior colliculus. It is argued that this tecto-geniculo-supragranular cortical pathway might convey W-cell information, as has been suggested for other species.