Long-range precise synchronous firing and receptive field encoding in the frog retina.

Long-range synchrony in the frog retina has been reported to be accompanied by oscillations. In this study, we found novel long-range synchronous firing without oscillatory activities. Spatially correlated visual stimuli were presented to the frog retina, after which spike responses from dimming detectors were analyzed to investigate the correlated spike activities and receptive fields (RFs). The results revealed precise synchronous firing from both adjacent cell pairs with overlapping RFs and cell pairs with distant RFs of up to 1,500 µm apart, even in the absence of oscillatory activities. Clear double-peaked cross correlograms were not detected. A considerable number of cell pairs exhibited RFs estimated from the synchronized spikes predominantly overlapped with those of one of the original cell pairs, suggesting that such synchronous firing can encode redundant spatial information. These results indicated the existence of a long-range neural substrate that generates precise synchrony among dimming detectors in response to spatially correlated stimuli. As the coincident spikes provide strong synaptic input to downstream neurons, synchronized spikes among dimming detectors might contribute to reliable signal transmission in the tectum, in which multiple retinal ganglion cells converge onto a single neuron.NEW & NOTEWORTHY In this study, we identified a novel form of long-range synchronous firing-occurring without oscillatory activities-among frog retinal ganglion cells known as dimming detectors. Spatially correlated visual stimuli evoked precise synchronous firing, even between cells with nonoverlapping receptive fields (RFs). RFs estimated from synchronized spikes predominantly overlapped with one cell's RF, suggesting redundant spatial coding. This synchronous firing might enhance reliable signal transmission from the retina to the tectum.