MECHANISMS OF CONCERTED FIRING AMONG RETINAL GANGLION-CELLS

Nearby retinal ganglion cells often fire action potentials in near syn chrony. We have investigated the circuit mechanisms that underlie thes e correlations by recording simultaneously from many ganglion cells in the salamander retina. During spontaneous activity in darkness, three types of correlations were distinguished: broad (firing synchrony wit hin 40-100 ms), medium (10-50 ms), and narrow (<1 ms). When chemical s ynaptic transmission was blocked, the broad correlations disappeared, but the medium and narrow correlations persisted. Further analysis of the strength and time course of synchronous firing suggests that nearb y ganglion cells share inputs from photoreceptors conveyed through int erneurons via chemical synapses (broad correlations), share excitation from amacrine cells via electrical junctions (medium), and excite eac h other via electrical junctions (narrow). It appears that the firing patterns in the optic nerve are strongly shaped by electrical coupling in the inner retina.