Evaluation of the stability and quality of sleep using Hjorth's descriptors.

Hjorth's descriptors (NSD) (activity, mobility, and complexity) provide a useful tool for evaluating micro- and macrostructural elements of sleep. In rats, the automatic analysis of sleep recordings by means of NSD calculated from SM and Vis derivations allow different sleep stages to be discriminated. Activity distribution over the total recording permits the definition of a global effect on the EEG. Moreover, the quality of sleep can be evaluated by the variations of the SM activity distribution by considering different classes of amplitude. Index and rate of unstable amplitude segments (UAS) constitute useful parameters to analyse the stability and quality of sleep with different models of insomnia and after pharmacological treatment. The UAS in rats can be compared to CAPs in humans. The NSD are also able to define quality and stability of human sleep. EEG analysis using NSD provides a novel perspective for the analysis of the stability and quality of rat and human sleep. This microstructural analysis of sleep appears to be a useful tool for pharmaco-EEG studies.