Receptive Fields of Monkey Geiuculate Cells in the Dark

RECEPTIVE FIELDS OF MONKEY GEIUCULATE CELLS IN THE DARK ADAPTED STATE. T.N.Wiesel & D.H.Hubel. Dept. of F’harm.,Harvard Med. School, Boston. Twelve cells in the dorsal layers of the lateral geniculate body of the Rhesus monkey were examined with monochromatic light-spot stimulation in both the light and dark adapted state. All cells had their receptive fields 3O to 18Ofrom the fovea. Four cells with opponent-color center-surround receptive fields showed an increase in the sensitivity of the center responses by about 3 log units; the peak spectral sensitivity of the center responses came to lie at about 500-520 mu,instead of at !&O or 580 mu in the light adapted state. The opposing surround showed no corresponding increase in sensitivity. Hence in the scotopic state at threshold levels these cells showed no opponent color mechanism, the spectral sensitivity was similar to that of rhodopsin, and the field had no center-periphery arrangement. These cells thus seemed to be supplied by both rods and cones; the rods seemed to play little part in the responses in the light adapted state, but dominated the responses at low intensities in the scotopic situation.In 6 other cells,also ones with opponent-color center-surround receptive fields, the threshold of both onand off-components fell with full dark adaptation by only l-l.5 log units, and there was little or no change in spectral sensitivity. This would be expected under our experimental conditions if all receptors supplying these cells were cones. Of the other type of opponent-color cell, in which the two antagonistic components had the same spatial distribution(i.e.,overlapped completely), only two were studied in the dark-adapted state, These seemed to receive input from cones only, since they showed only a moderate decrease in threshold and no change in spectral sensitivity of the two components. In summary, some geniculate cells appear to be connected to both rods and cones, others to cones only.