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 distribution and by a decreased metabolic rate compared to a normal night of sleep. The present study examined whether sleep during a period of increased metabolic rate was less restorative than a normal period of sleep. Twelve normal young adults participated for two 4-day periods. In each period, an undisturbed baseline sleep night was followed by baseline testing. On the subsequent night, Ss slept a total of 212 min, starting at 0200 h after consuming placebo or 400 mg of caffeine. After the nap, subjects remained awake for 41 h until beginning an undisturbed night of recover sleep. During the period of sleep loss, subjects remained 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 was an increase in stage 1 and a decrease in stage 4 sleep after caffeine use. Performance on addition and vigilance tasks was significantly decreased after the caffeine plus nap condition. However, no significant difference were found on the MSLT, and subjective vigor was significantly greater following the caffeine and nap combination. It was concluded that the beneficial effect of sleep in maintaining performance was decreased by increased physiological activation during sleep.