The microstructure of sleep in primary insomnia: an overview and extension.

The present review was undertaken to summarize studies elucidating sleep microstructural differences in chronic insomnia. The etiology of insomnia is still unknown, whereas the hyperarousal concept has gained much attention with respect to pathophysiology. According to this model, insomnia is characterized by significant hyperarousal on an autonomous and central nervous level. Objective findings derived from polysomnography frequently show much less severe differences to good sleepers than subjective sleep complaints assessed by self-rating questionnaires. However, using more fine-grained methods to characterize the electrophysiology of sleep in insomnia, rather distinct differences between the sleep of good sleepers and patients with insomnia have been noted. These methods include the spectral analysis of the sleep EEG, micro-arousal and CAP (cyclic alternating pattern) analysis as well as the assessment of event-related potentials (ERPs) during night-sleep. The application of these methods shows stronger correlations with the subjective experience of disturbed sleep than standard sleep EEG scoring. An overview of the relevant empirical evidence is presented, previous investigations are extended and a theoretical synthesis within the framework of the hyperarousal concept of insomnia is attempted.