How do OFF-center ganglion cells respond to a decrease in light exposure?

OFF-center ganglion cells are a type of retinal ganglion cell that are primarily excited by light stimulating the surround region of their receptive field and inhibited by light in their center region. When there is a decrease in light exposure, the area within the center of these ganglion cells that previously experienced a higher intensity of light now has reduced illumination. Consequently, this decrease in light effectively removes the inhibitory signal that the surrounding light had on these cells.

As the level of illumination in the center decreases, the release of the neurotransmitter glutamate from photoreceptors (rods and cones) also decreases. This reduction in glutamate causes the postsynaptic receptors of OFF-center ganglion cells to become less stimulated, leading to a change in membrane potential.

In this situation, the OFF-center ganglion cells depolarize, meaning they become more positive in charge, which, in turn, increases their likelihood of firing action potentials. This response allows the visual system to signal changes in light intensity effectively, particularly in darker regions of the environment. Thus, the appropriate response of OFF-center ganglion cells to a decrease in light exposure is depolarization.