Lagged Y cells in the cat lateral geniculate nucleus

We report on the existence of lagged Y (Y_L) cells in the A laminae of the cat lateral geniculate nucleus (LGN) and on criteria for identifying them using visual and electrical stimulation. Like the lagged X (X_L) cells described previously (Mastronarde, 1987a; Humphrey & Weller, 1988a), Y_Lcells responded to a spot stimulus with an initial dip in firing and a delayed latency to discharge after spot onset, and an anomalously prolonged firing after spot offset. However, the cells received excitatory input from retinal Y rather than X afferents, and showed nonlinear spatial summation and other Y-like receptive-field properties. Three Y_Lcells tested for antidromic activation from visual cortex were found to be relay cells, with long conduction latencies similar to those of X_Lcells. Simultaneous recordings of a Y_Lcell and its retinal Y afferents show striking parallels between lagged X and Y cells in retinogeniculate functional connectivity, and suggest that the Y_L-celI response profile reflects inhibitory processes occurring within the LGN. The Y_Lcells comprised ~5% of Y cells and —1% of all cells in the A laminae. Although infrequently encountered in the LGN, they may be roughly as numerous as Y cells in the retina, and hence could fulfill an important role in vision.