Light adaptation of human rod receptors: the leading edge of the human a-wave and models of rod receptor activity

The human rod receptors can be studied by measuring the leading edge of the rod a-wave of the ERG. Computational models, previously shown to fit the recordings from single rods, are fitted to dark-adapted a-wave responses. A model proposed by Lamb and Pugh [(1992) Journal of Physiology, 499, 719-758] fits slightly better than the traditional models based upon n-stage exponential filters. To test alternative models of rod light adaptation, a-waves were recorded to flashes presented upon steady adapting lights. Steady adapting lights decrease the rods' sensitivity. Human rods must adapt as response compression alone predicts far greater decreases in sensitivity. The evidence suggests that the mechanism(s) of adaptation include a change in the time-course of the rod's response. Human rods appear to adapt in much the same manner as do the rods of other vertebrates.