Auditory arousal thresholds after selective slow-wave sleep deprivation

Objectives: The aim of this study is to assess Auditory Arousal Thresholds (AATs) three times during an undisturbed baseline night and to compare them to AATs during the recovery night that follows two consecutive nights of s elective SWS deprivation. The presence of a time-of-night effect on AATs wi ll also be assessed. Methods: Ten male Ss slept in the laboratory for 6 consecutive nights. The first two nights were undisturbed. The 3rd night was considered as baseline . During the 4th and 5th nights, selective SWS deprivation was obtained by means of acoustic stimulation. The 6th night was a recovery. In the last 4 nights Ss were awakened three times, after 2, 5 and 7.5 h of sleep, respect ively. All the awakenings were carried out from stage 2 (after at least 5 c onsecutive min of stage 2), by means of 1000 Hz ascending tone series. The AAT determination was based on EEG-EMG criteria: at least 10-s of clear alp ha rhythm and/or a 10 s movement arousal. Results: During both deprivation nights, SWS amount was close to zero. In t he ensuing recovery night a significant SWS rebound was found, accompanied by a significant increase of AATs with respect to the baseline. Furthermore , there was a significant linear decrease of AATs during the night. Finally , the individual correlations between AATs and SWS amount were significant in 4 out of 10 Ss. Conclusions: These results confirm that AATs are a reliable index of sleep depth by showing that the SWS rebound following selective SWS deprivation i s paralleled by a significant AAT enhancement. The experimental paradigm al so allows us to claim that AATs show a decreasing linear trend during the n ight, having excluded any procedural bias. Finally, AATs can be directly re lated to SWS amount that preceded the awakening, although the individual co rrelations between AATs and SWS have to be considered with caution, given t he high inter-subject variability and the small number of observations. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.