Temporal coding of visual information in the thalamus

The amount of information a sensory neuron carries about a stimulus is dire ctly related to response reliability. We recorded from individual neurons i n the cat lateral geniculate nucleus (LGN) while presenting randomly modula ted visual stimuli. The responses to repeated stimuli were reproducible, wh ereas the responses evoked by nonrepeated stimuli drawn from the same ensem ble were variable. Stimulus-dependent information was quantified directly f rom the difference in entropy of these neural responses. We show that a sin gle LGN cell can encode much more visual information than had been demonstr ated previously, ranging from 15 to 102 bits/sec across our sample of cells . Information rate was correlated with the firing rate of the cell, for a c onsistent rate of 3.6 +/- 0.6 bits/spike (mean +/- SD). This information ca n primarily be attributed to the high temporal precision with which firing probability is modulated; many individual spikes were timed with better tha n 1 msec precision. We introduce a way to estimate the amount of informatio n encoded in temporal patterns of firing, as distinct from the information in the time varying firing rate at any temporal resolution. Using this meth od, we find that temporal patterns sometimes introduce redundancy but often encode visual information. The contribution of temporal patterns ranged fr om -3.4 to -25.5 bits/sec or from -9.4 to +24.9% of the total information c ontent of the responses.