Perceptual and physiological consequences of dark adaptation: a TMS-EEG study.

Background: One of the most important functions of the visual system is the sensitivity to variation of the environment light. In the present study we aimed at assessing cortical modulation as a function of environmental light adaptation through directly linking subjective report (i.e., phosphene perception) with neurophysiological correlates (i.e., transcranial magnetic stimulation (TMS)-evoked potentials, TEPs). Methods: Ten young healthy participants underwent 30 minutes of light and 30 minutes of dark adaptation in counterbalanced order. We measured TMS-induced phosphene perception through the method of constant stimuli (11 TMS intensities from 46 to 76% of the maximal stimulator output) after each condition while 32-channels electroencephalogram (EEG) was continuously recorded. A Weibull function was fitted to phosphene report in order to estimate threshold and slope of the psychometric functions. Results: Dark adaptation modulated visual perception: the slope of the psychometric function after dark adaptation significantly increased compared to light adaptation. A preliminary analysis of TMS-EEG data shows a modulation of TEPs amplitude after dark adaptation.