Lagged Y cells in the cat lateral geniculate nucleus

Abstract

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_L cells 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_L cells tested for antidromic activation from visual cortex were found to be relay cells, with long conduction latencies similar to those of X_L cells.Simultaneous recordings of a Y_L cell and its retinal Y afferents show striking parallels between lagged X and Y cells in retinogeniculate functional connectivity, and suggest that the Y_L-cell response profile reflects inhibitory processes occurring within the LGN. The Y_L cells 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.