IDENTIFICATION, CLASSIFICATION AND ANATOMICAL SEGREGATION OF CELLS WITH X-LIKE AND Y-LIKE PROPERTIES IN LATERAL GENICULATE-NUCLEUS OF OLD-WORLD PRIMATES

All the cells (158) studied in the lateral geniculate nuclei of Macaca nemestrina and M. irus could be distinguished as either X-like or Y-like on the basis of their responses to tests developed to classify cat retinal and lateral geniculate nucleus cells. These tests included responses to stationary spots, fast moving wands and moving gratings. Response latencies to electrical stimulation of the optic chiasm were determined for 130 cells; no X-like cell showed a latency shorter than 1.7 ms, no Y-like cell showed a latency longer than 1.6 ms. Primate lateral geniculate nucleus cells with X-like properties thus received their excitatory input from retinal cells with slowly conducting axons, and these most probably include the tonic ganglion cells described by Gouras; Y-like lateral geniculate nucleus cells were driven by retinal cells with faster conducting axons, most probably including the phasic ganglion cells described by Gouras. Wiesel and Hubel classified monkey lateral geniculate nucleus cells into 4 main types based on their receptive-field properties, as revealed by spectrally and spatially distinct stimuli. All Type I and Type II cells showed X-like properties; all type IV cells showed Y-like properties. Type III consisted of a subtype that showed X-like properties, here termed Type IIIx, and subtype that showed Y-like properties, here termed Type IIIy. The 1st cells encountered as the micro-electrode reached the lateral geniculate nucleus were always X-like. In some penetrations only X-like cells were encountered as the electrode moved downward through the lateral geniculate nucleus. In the remaining penetrations, after recording X-like cells through most of the lateral geniculate nucleus, Y-like cells were than encountered. No X-like cells were found below Y-like cells. Thus these 2 classes of cells are anatomically segregated within the primate lateral geniculate nucleus. Electrode marking showed the border between X-like and Y-like cells to correspond to the border between the parvo- and magnocellular layers of the lateral geniculate nucleus. Thus X-like cells (i.e., Types I, II and IIIx) occurred in the parvocellular layers, and Y-like cells occurred (i.e., Types IIIy and IV) in the magnocellular layers.