Maintained activity of lateral geniculate nucleus neurons as a function of background luminance

Abstract

The maintained activity of single lateral geniculate nucleus (LGN) neurons was recorded from anesthetized cats as a function of background luminance. Neuronal activity was recorded at 5 luminance levels ranging from complete darkness to 25-ft L. Both transient and steady-state neuronal activity was recorded at each luminance level. In some LGN neurons increasing the background luminance caused a systematic rise in their firing rate; in other LGN neurons luminance increments caused a systematic depression of firing rate. The firing rate of a few LGN neurons was not affected systematically by successive luminance changes. Generally, immediately after each luminance change there was a pronounced effect on the maintained discharge of most LGN neurons; this effect decreased in magnitude as time lapsed, but was still clearly present 15 min after the luminance change. The above results suggest that at least some LGN neurons signal, to the visual cortex, the absolute level of ambient luminance by changes in their maintained discharge rate.