Maintained activity of cat retinal ganglion cells.

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Abstract
The statistical character of the maintained firing in light and dark of cat retinal ganglion cells was investigated. Despite uniform conditions, there was a wide variability in mean firing rate from unit to unit and with time in the same unit. This variability was not, in general, due to damage but depended on the presence of contrast in the visual field. There is a weak but significant statistical correlation between the adjacent interspike time intervals of most units. This correlation could be positive or negative and was greatest for off-center units. No significant statistical difference was found between the firing patterns of on-center or off-center units in light or dark. The firing pattern following an action spike was investigated, shown to depend on both ganglion cell properties and the levels of synaptic inputs but not, in general, on the time pattern within the structure of the synaptic input. Simultaneous recording from nearby units in 3 of 5 instances revealed the presence of a statistical correlation in their firing patterns. This correlation was due to a shared synaptic input from bipolar cells and/or amacrine cells. Chemical destruction of photoreceptors caused a loss of the maintained activity of ganglion cells. Hypotheses, based on these data, as to the nature of maintained activity and receptive field organization were presented and discussed.