Correlation of activity in neighbouring goldfish ganglion cells: relationship between latency and lag

Pairs of retinal ganglion cells in the isolated goldfish retina were recorded simultaneously with a single electrode. Repeated flashes of light were delivered to evaluate the response latency of each of the units. The cross-correlation histogram for the maintained discharge of each pair of cells was examined, and its temporal relationships (lags) were compared with the differences in response latencies of the two units. There was a strong correlation between these measures; however, the differences between latencies were often at least twice as great as the lags. The differences between the times to the peaks of the responses of the two units were less reliably related to the lags of the pairs, although the correlation was positive and the differences in time-to-peak generally greater than the lags. The weaker relationship between the difference in time-to-peak and lag than between latency difference and lag is apparently a manifestation of a negative correlation between latency and rise time (from first response to peak). This indicates that cells with a longer latency compensate with a faster rise time. There was a negative correlation between the mean maintained rate of a neurone and its response latency. That is, cells with faster maintained discharge rates respond sooner than those with slower maintained rates. There was virtually no relationship between the lags or the differences in latency and the differences between the magnitudes of the responses to light. Thus, it is unlikely that differences in latency (or lags) could be attributed to unequal effectiveness of the stimuli for the two units. The relationship between differences in latency and lags did not depend on the response categorizations of the two units. Specifically, it did not matter whether the members of the pair were on centre, off centre or on-off centre; neither did it matter whether they were X-like or not-X-like neurones. Consideration of these data leads to the conclusion that there must be 'marked' pathways of differential conduction velocity through the retina.