Temporal and Spatial Dependence of Adaptation on Ganglion Cells

One of the visual system’s many tasks is to be able to distinguish objects from the background. The ability to do this is limited and affected by the relationship between the object (or stimulus) of interest and the background. Adaptation in retinal neurons is the process of changing the cell’s response to a stimulus according to that stimulus’s background. When the stimulus is hard to discern from the background, the retina adapts by improving its sensitivity to low contrast. The large response range maintained by adaptation comes at a cost, however. Adaptation complicates neural coding by making the brain interpret identical stimuli as different based on differences in background. In order to further our understanding of adaptation, this study modified the background to be in terms of time and space rather than light intensity as is the norm. By changing the interval between two circular stimuli (inter-stimuli interval; IsI) of the same diameter, and by changing the diameter over a common IsI, we measured a ganglion cell’s output for one stimulus relative to another stimulus. the results show saturation (loss of output to the 2nd stimulus) of stimuli at lower IsIs. Also, the degree of saturation for a given IsI depends on the diameter of the stimulus. These combinations of results illustrate the temporal and spatial dependence of adaptation on ganglion cells. A larger-diameter stimulus involves multiple neurons surrounding the ganglion cell being recorded so various pathways most likely influence that cell’s ultimate output. Rapid stimuli (low IsI) can be defined as having large mean luminosity that directly affects ganglion cell output