Local and Global Contrast Adaptation in Retinal Ganglion Cells
Retinal ganglion cells react to changes in visual contrast by adjusting their sensitivity and temporal filtering characteristics. This contrast adaptation has primarily been studied under spatially homogeneous stimulation. Yet, ganglion cell receptive fields are often characterized by spatial subfields, providing a substrate for nonlinear spatial processing. This raises the question whether contrast adaptation follows a similar subfield structure or whether it occurs globally over the receptive field even for local stimulation. We therefore recorded ganglion cell activity in isolated salamander retinas while locally changing visual contrast. Ganglion cells showed primarily global adaptation characteristics, with notable exceptions in certain aspects of temporal filtering. Surprisingly, some changes in filtering were most pronounced for locations where contrast did not change. This seemingly paradoxical effect can be explained by a simple computational model, which emphasizes the importance of local nonlinearities in the retina and suggests a reevaluation of previously reported local contrast adaptation. º Contrast adaptation acts mostly on entire receptive field of retinal ganglion cells º Additional minor contributions to adaptation occur locally in subfields º Local nonlinearities mediate surprising action at a distance of adaptation º Local nonlinearities may feign local adaptation in cross-adaptation experiments Retinal ganglion cells adapt to changes in visual contrast. To examine whether this adaptation always affects entire receptive fields or can be confined to subfields, Garvert and Gollisch measure how ganglion cell signal processing is influenced by local contrast changes.