DAYTIME VIGILANCE AFTER MORNING BRIGHT LIGHT EXPOSURE IN VOLUNTEERS SUBJECTED TO SLEEP RESTRICTION

This study was designed to test the hypothesis that bright light (BL) can have a stimulating effect on vigilance even in the absence of supp ression of melatonin secretion and that this effect can be detected wh en measured in subjects with low vigilance levels. Seven normal subjec ts were exposed to bright-white light (BL group) and seven to dim-red light (DL group) on 2 consecutive days, each following a night of 4-h sleep restriction. The light treatment was administered in the late mo rning, between 0900 and 1330 hours. Salivary melatonin measurements in dicated that BL did not suppress melatonin secretion or induce circadi an phase shifts. The effects of the two treatments were compared on va lidated measures of daytime vigilance: immediate effects were evaluate d on subjective alertness during the light treatment, whereas short-te rm (0.5-10.5 h) and long-term (20.5-34.5 h) carryover effects were mea sured on subjective alertness, daytime sleep latencies (DSL), and psyc homotor performance. After two nights of sleep restriction, subjective alertness and daytime sleep latencies decreased significantly, but th ere was no effect of the light treatment. BL treatment did not affect global performance, but there was an effect on the strategy used by th e subjects, as shown by faster reaction times and increased percentage of errors in the BL group. It was concluded that daytime BL exposure did not have a stimulating effect on our measures of vigilance even in sleep-deprived subjects but that it may increase physiological arousa l and affect the subjects' behavior in some specific performance tasks . (C) 1998 Elsevier Science Inc.