Abstract
Neurons are often assumed to encode only one time-varying quantity, e.g. similarity between visual input and receptive fields, concentration of specific odorants, distance from specific locations, etc. However, when a neuron generates N spikes, there are N-1 interspike intervals. If these interspike intervals are on time scale much shorter than that of input modulation, they could, theoretically, encode up to N-1 quantities characterizing the input waveform. Here we show that the vertebrate retina performs such coding. In response to various visual inputs, retinal ganglion cells generate highly reproducible spike bursts, characterized by clusters of spikes separated by hundreds of milliseconds of silence. We asked if spike patterns, i.e., combinations of interspike intervals within these bursts, carry information about visual input. With multielectrode recoding from the retinas of salamanders and mice, we found that a subset of ganglion cells generate bursts with various spike patterns, which are unique to the preceding visual inputs. Surprisingly, when single bursts contain three spikes, the two interspike intervals nonlinearly encode two independent components of the preceding light intensity waveforms. Although these spike patterns are on time scales of a few milliseconds, they encode visual input as long as 400 milliseconds. Recordings from LGN slices indicated that the retinogeniculate synapses are reliable enough to transmit the information. We conclude that single ganglion cells encode multiple quantities in the form of burst spike patterns, and reliably transmit them to the brain. [J Physiol Sci. 2007;57 Suppl:S11]
