Ow Efficiently a Ganglion Cell Codes the Visual Signal

stract-The retina’s visual message is transmitted to the brain ganglion cells that integrate noisy synaptic inputs to create a ike train. We asked how efficiently the retinal ganglion cell ike generator creates the spike train message. Intracellular d extracellular recordings were made from in vitro guinea pig tina, in response to a spot of light flashed over the receptive ld center. Responses were analyzed with an "ideal observer," program that discriminated between two contrasts based on optimal decision rule. Spike trains from ganglion cells had resholds as low as 1% contrast, but thresholds for the corsponding graded potentials were lower by a factor of 2. Using computational model of the ganglion cell, we asked what facrs in the spike generator mechanism are responsible for the ike train’s loss in performance. The model included ndritic/axonal morphology, noisy synaptic inputs and memane channels. Adaptation of spike rate was provided by (Ca) channels which were activated by Ca2+ flux during ikes. When K(Ca) channels were included, they controlled the ration of the inter-spike interval and thus set the level of noise the spike train. These results imply that the spike generator ds noise to the spike train signal.