SummaryThe difficulty to recruit homogeneous samples of insomniacs requires alternative approaches for sleep studies. Acoustic perturbation in healthy volunteers made it possible to determine an experimental model of acute situational insomnia in order to investigate the effects of classic and novel hypnotic compounds. Unfortunately, the traditional scoring parameters of sleep are inadequate to provide reliable information for defining the neurophysiological bases of insomnia and for evaluating the efficacy of hypnotic drugs. Recent studies on the microstructure of sleep have permitted to identify a specific EEG feature, the cyclic alternating pattern (CAP), correlated with the subjective appreciation of sleep quality. Comparing placebo, zolpidem, zopiclone, lorazepam and triazolam, given at equivalent therapeutic doses in middle-aged healthy volunteer subjects under basal conditions and under acute situational insomnia, provided non-significant information when using classical sleep parameters whereas CAP rate (the percentage ratio of CAP time to non-REM sleep time) permitted to discriminate the basal nights from the perturbed nights and the drug nights from the placebo nights. These data have been confirmed in clinical studies using zolpidem versus placebo in chronic insomniacs.