What is an off-response in a retinal ganglion cell?

An off-response in a retinal ganglion cell is a physiological phenomenon characterized by a powerful discharge of action potentials that occurs specifically when a light stimulus is switched off.12

In the context of the retina's receptive field, which typically features a concentric centre-periphery organization, the off-response is often associated with the inhibitory regions of the cell. For example, in an on-centre cell, the peripheral ring of the receptive field is inhibitory; when light falls on this periphery, the cell's background discharge is suppressed while the light is on, followed by a pronounced burst of activity—the off-response—the moment the light is extinguished.13

This mechanism reveals the inhibitory nature of certain synaptic pathways in the visual system. By responding to the cessation of light, these cells help the brain detect changes in illumination, such as the movement of shadows or contours, rather than simply signaling the presence of constant light.24