Abstract
Lateral geniculate neurons differ from simple “integrate and fire” behaviour in that they exhibit a low-threshold transient Ca2+ conductance. This leads to two distinct response modes: “tonic”, in which the spike timing is relatively unstructured, and “burst mode”, involving temporal clustering of the spikes. What are the properties of these distinct modes of firing for the transmission of retinal information to the cortex? We investigated this question by simulating an “integrate and fire or burst” model (Smith et al J. Neurophys. 83:588–610) of an LGN cell with synaptic input, and analysing its output using information theoretic procedures.
The information in the spike train was broken down into components reflecting the PSTH and autocorrelations using the approach of Panzeri and Schultz (Neural Computation 13(6):1311–1349). This also allowed the redundancy between the information contribution of individual spikes to be examined. We found that bursts lead to a higher information contribution from the PSTH than tonic firing, and this tends to be coupled with a negative contribution due to correlations between spikes. The consequence of this is that burst mode may have a higher instantaneous information rate, but that this is moderated over time by greater redundancy between spikes. The size of this effect depends upon the relative amounts of spontaneous input and retinal drive. We interpret this as consistent with the possibility that bursts may play a role in transient “updating” of the cortex, but that tonic firing is required for sustained information transfer in the aroused state.