Voluntary oculomotor performance upon awakening after total sleep deprivation

The potential impact of sleep inertia on measures of voluntary oculomotor control have been surprisingly neglected. The present study examined the effects of 40 hours of sleep deprivation on saccadic (SAC) and smooth pursuit (SP) performance, attentional/visual search performance (Letter Cancellation Task, LCT) and subjective sleepiness (Sleepiness Visual Analog Scale, SVAS) recorded immediately after awakening. Standard polysomnography of nine normal subjects was recorded for 3 nights (1 adaptation, AD; 1 baseline, BSL; 1 recovery, REC); BSL and REC were separated by a period of 40 h of continuous wakefulness, during which subjects were tested every two hours. Within 30 s of each morning awakening, a test battery (SAC, SP, LCT, SVAS) was administered to subjects in bed. For data analysis, mean performance obtained during the day preceding the sleep deprivation night was considered as "Diurnal Baseline" and compared to performance upon awakening from nocturnal sleep. As a consequence of sleep deprivation, SWS percentage was doubled during REC. Saccade latency increased and velocity decreased significantly upon awakening from REC as compared to the other three conditions (Diurnal baseline, AD awakening, BSL awakening); accuracy was unaffected. As regards SP, phase did not show any impairment upon awakening, while velocity gain upon awakening from REC was significantly lower as compared to the other conditions. Finally, number of hits on LCT upon awakening from REC was significantly lower and subjective sleepiness higher as compared to Diurnal Baseline. It is concluded that 40 h of sleep deprivation significantly impaired performance to SAC and SP tasks recorded upon awakening from recovery sleep. This performance worsening is limited to the measures of speed, while both SAC accuracy and SP phase do not show a significant decrease upon awakening. Since saccadic velocity has recently been found to negatively correlate with simulator vehicle crash rates, it is suggested that the adverse effects of sleep deprivation on sleep inertia magnitude should be avoided by any personnel who may have to perform critical tasks involving high oculomotor control immediately after awakening.