Cortico-cortical projections from striate cortex of the squirrel monkey (Saimiri sciureus). A radioautographic study.

In 13 squirrel monkeys [3H] leucine was injected into three different portions of the striate cortex: the occipital convexity, the interhemispheric surface and the depth of the calcarine fissure. After survival times between 8.5 h and 23 days. The radioautographic study of the brains revealed terminal fields of projection in various cortical areas outside the striate cortex. Transport of labelled material to cortex close to the striate area and in the superior part of the supratemporal sulcus occurred in all cases. After injection into the striate cortex of the interhemispheric surface, or into the depth of the calcarine fissure, a second projection was found in the prestriate belt situated in the cortex near the parieto-occipital sulcus. The fields of projection in the 3 cortical regions varied systematically with the variation of the injection site indicating a retinotopic organisation. If the cortical labelling was restricted to the supragranular layers, intracortical projection to layer V could be observed. If the cortical injection labelled only the infragranular layers, an intracortical projection appeared clearly at the level of layer IIIc. Labelling restricted to the supragranular layers resulted in cortico-cortical projections whereas labelling of only the infragranular layers did not. In the 3 cases in which the contralateral hemisphere was examined no evidence for transcallosal projections was found.