The responses of cells in macaque lateral geniculate nucleus to sinusoidal gratings

Responses of cells in the parvocellular (p.c.l.) and magnocellular (m.c.l.) layers of the macaque lateral geniculate nucleus to sine-wave gratings were studied. Both p.c.l. and m.c.l. cells responded best at a temporal frequency (drift rate) of 10-20 Hz. P.c.l. cells responded at temporal frequencies lower than 1 Hz; m.c.l. cells did not. With coloured- or white-black luminance-modulated gratings, responses of m.c.l. cells were weaker at low than at medium spatial frequencies. With coloured gratings, p.c.l. cell responses were not attenuated at low spatial frequencies. With white gratings a few p.c.l. cells did show such attenuation. Optimal responses from p.c.l. cells were obtained with coloured gratings; white gratings evoked weaker responses. With a grating of a colour causing suppression of a p.c.l. cell's activity, the modulation of firing was much less than with a grating of a colour excitatory for the cell. M.c.l. on- and off-centre cells responded equally well to moving gratings. The ability of p.c.l. cells to resolve fine gratings was dependent on cell type as well as on the colour of grating used. The ability of m.c.l. cells to resolve fine gratings was comparable to that of p.c.l. cells. The contrast sensitivity of m.c.l. cells was much higher than that of p.c.l. cells. This may account for their ability to resolve fine gratings, despite their larger centre size. In comparison with luminance-modulated gratings, chromatically modulated gratings could evoke larger or smaller responses, depending on p.c.l. cell type and the colours in the grating. M.c.l. cells responded poorly or not at all.