METABOLIC-RATE AND THE RESTORATIVE FUNCTION OF SLEEP

It has been shown that performance improves during sleep more rapidly after sleep deprivation than during normal sleep. Recovery after sleep deprivation is also characterized by a different sleep stage distribu tion and by a decreased metabolic rate compared to a normal night of s leep. The present study examined whether sleep during a period of incr eased metabolic rate was less restorative than a normal period of slee p. Twelve normal young adults participated for two 4-day periods. In e ach period, an undisturbed baseline sleep night was followed by baseli ne testing. On the subsequent night, Ss slept a total of 212 min, star ling at 0200 h after consuming placebo or 400 mg of caffeine. After th e nap, subjects remained awake for 41 h until beginning an undisturbed night of recovery sleep. During the period of sleep loss, subjects re mained at the sleep laboratory where they performed computer tests and MSLTs, The caffeine produced a significant increase in metabolic rate during the nap. Although total sleep time was held constant, there wa s an increase in stage 1 and a decrease in stage 4 sleep after caffein e use. Performance on addition and vigilance tasks was significantly d ecreased after the caffeine plus nap condition. However, no significan t differences were found on the MSLT, and subjective vigor was signifi cantly greater following the caffeine and nap combination. It was conc luded that the beneficial effect of sleep in maintaining performance w as decreased by increased physiological activation during sleep.