At the beginning of dark adaptation there is a sudden decrease of threshold that appears distinct from the subsequent course of regular dark adaptation. The present research indicates that the decrease cannot be a result of losing the lateral inhibitory effects that occurred during the light adaptation prior to dark adaptation. The results thus imply that the early threshold drop must be based on a process somewhere in the direct line from receptor to higher centers.
Howard D. Baker, "Area effects and the rapid threshold decrease in early dark adaptation," J. Opt. Soc. Am. 63, 749-754 (1973)