Figure 1.

Gap junctions between ganglion cells mediate fine-scale correlated activity. (a) A cartoon cross-section of the inner retina, depicting glutamatergic bipolar cells terminals (blue triangles) synapsing onto electrically coupled RGCs, labeled in the Hb9::eGFP retina (green cells; for simplicity only the ON dendrites are drawn). The flash used to stimulate the photoreceptors (not shown) is illustrated by the yellow bar. The vertical and horizontal arrows indicate chemical and reciprocal electrical synapses, respectively. (b) Spike trains evoked by a high-contrast spot (300-μm diameter, 10 trials), measured simultaneously from a pair of neighboring cRGCs (C1 and C2), are synchronized on a broad timescale by the stimulus. (c) A high temporal resolution view of a portion of the ON response shown in b illustrates fine-scale correlated spikes (highlighted by gray boxes, 2 ms) that are independent of the stimulus. (d) A cross-correlogram that indicates the distribution of spike times measured in C2 relative to each spike in C1 (0.5-ms bins). Inset shows the fine-scale correlated peaks in the cross-correlogram at higher temporal resolution. (e) The bimodal peaks (within ±2 ms) in the cross-correlogram were abolished in the presence of the gap junction blocker 18βGA (25 μM). Correlations were also weaker between Hb9⁺ cells in Cx36^−/− retina (Supplementary Fig. 5). (f) Polar plots (top left) indicating the peak spike rate (normalized to the preferred direction) evoked by stimuli moving in eight directions, measured simultaneously in a pair of uncoupled directionally selective ganglion cells (C1 and C2) coding different directions. Gaussian approximations of their receptive fields, indicating the high degree of receptive field overlap between C1 and C2 (bottom left, Online Methods). Right, cross-correlogram for light-evoked spike activity for this pair of uncoupled RGCs. D, dorsal; N, nasal; V, ventral; T, temporal.