The relationship between frequency of rapid eye movements in REM sleep andSWS rebound

Previous studies have shown a decrease in rapid eye movement (REM) frequenc y during desynchronized sleep in recovery nights following total or partial sleep deprivation. This effect has been ascribed to an increase in sleep n eed or sleep depth consequent to sleep length manipulations. The aims of th is study were to assess REM frequency variations in the recovery night afte r two consecutive nights of selective slow-wave sleep (SWS) deprivation, an d to evaluate the relationships between REM frequency and SWS amount and au ditory arousal thresholds (AAT), as an independent index of sleep depth. Te n normal males slept for six consecutive nights in the laboratory: one adap tation, two baseline,two selective SWS deprivation and one recovery night. SWS deprivation allowed us to set the SWS amount during both deprivation ni ghts close to zero, without any shortening of total sleep time. In the ensu ing recovery night a significant SWS rebound was found, accompanied by an i ncrease in AAT. In addition, REM frequency decreased significantly compared with baseline. This effect cannot be attributed to a variation in prior sl eep duration, since there was no sleep loss during the selective SWS depriv ation nights. Stepwise regression also showed that the decrease in REM freq uency is not correlated with the increase in AAT, the traditional index of sleep depth, but is correlated with SWS rebound.