Abstract
One of the most important functions of the visual system is to dynamically adapt to changing environments. A well-known neuronal phenomenon underlying such adaptation is a decline in visual response after prolonged or repeated visual exposure. Previous work suggests that visual adaptation in primates occurs primarily in the cortex. There is also evidence for limited pre-cortical adaptation. Specifically, single neuron recordings in anesthetized macaques revealed that adaptation induced by high-contrast gratings is exclusive to the magnocellular (M) cell class of the lateral geniculate nucleus of the dorsal thalamus (LGN). No such adaptation was found for the parvocellular (P) and koniocellular (K) cell classes. Here, we examine response adaptation among LGN neurons in awake macaques. Animals fixated on a computer screen while we presented drifting gratings of varying contrast for prolonged periods of time (>1s). While the animals performed this task we recorded visual responses of one or more of their LGN neurons using linear multielectrode arrays. We determined each unit’s receptive field location as well as the cell subtype (M, P, or K) using cone-isolating stimuli and other physiological criteria such as the transience of the visual response and contrast response functions. We computed the decline of each unit’s visual response across grating cycles. We found that although weak adaptation occurred in some M, P and K neurons, there was no significant adaptation at the group level. These results suggest that some effects of visual adaptation can be observed in the LGN of awake behaving primates, and that these effects are not limited to one class of LGN neurons. Nevertheless, in line with previous observations, we found that a substantial majority of LGN neurons do not show significant visual adaptation.