Dark adaptation within the receptive field centre of rat retinal ganglion cells.

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Abstract
Recordings from single axons of retinal ganglion cells in the rat''s optic tract were used to determine whether bleaching a small area of the receptive field reduced sensitivity globally or locally, near the bleached photoreceptors. When a suprathreshold test spot was alternated between 2 equally sensitive positions, the ganglion cell gave an approximately balanced response. The balance was upset if a small-spot bleach was selectively applied to 1 position. Recovery of the balanced condition was rapid. Varying the duration of a constant illuminance bleach varied the duration of the imbalance following the bleach. The recovery of sensitivity after small-spot bleaches was measured at the location of the bleach and at another location, initially equally sensitive. The recovery at the bleached location lagged recovery at the unbleached location; but even in the bleached location, the return of sensitivity was rapid. Recovery of sensitivity after half-field bleaches was measured in the bleached and unbleached halves of the receptive field. Recovery in the bleached half lagged behind the unbleached half. A comparison between the effects of a small-spot bleach and a half-field bleach of the same strength showed the duration of dark adaptation depends on the area of the bleach.