Figure 3.

Mechanisms underlying synchronized firing in primate retinal ganglion cells (Rieke, Shlens & Chichilnisky, unpublished results). (a) Schematic representation of two kinds of connectivity that could mediate synchronized firing. (b) The cross-correlogram between adjacent ON parasol cells often exhibits a bimodal shape. This feature suggests reciprocal coupling, potentially mediated by gap junctions. (c) The cross-correlogram between adjacent OFF parasol cells does not exhibit a bimodal shape, suggesting that common input may dominate synchronized firing. (d,e) Intracellular recordings from pairs of ON and OFF parasol cells indicate that synaptic currents are highly correlated. Each cell was voltage-clamped at the resting potential of inhibition to isolate excitatory synaptic currents. The cross-correlation of the intracellular currents indicate that the time scale and magnitude of the correlated synaptic inputs roughly match the observed synchronized firing (b,c). Thus, common synaptic input appears to account for a major component of synchronized firing in both ON and OFF parasol cells.