Contrast and luminance gain control in the macaque'slateral geniculate nucleus
In natural scenes, there is substantial variation in the mean and fluctuation of light levels (luminance and contrast). Retinal ganglion cells maintain their sensitivity despite this variation and their limited signaling bandwidth using two adaptive mechanisms, which control luminance and contrast gain. However, the signature of each mechanism and their interactions further downstream of the retina are unknown. We recorded neurons in the magnocellular and parvocellular layers of the lateral geniculate nucleus (LGN) in anesthetized adult male macaques and characterized how they adapt to changes in contrast and luminance. As contrast increases, neurons in the magnocellular layers maintain sensitivity to high temporal frequency stimuli but attenuate sensitivity to low temporal-frequency stimuli. Neurons in the parvocellular layers do not adapt to changes in contrast. As luminance increases, magnocellular and parvocellular cells increase their sensitivity to high temporal frequency stimuli. Adaptation to luminance is independent of adaptation to contrast, as previously reported for LGN neurons in the cat. Our results are similar to those previously reported for macaque retinal ganglion cells, suggesting that adaptation to luminance and contrast result from two independent mechanisms that are retinal in origin.