A vigilance state is characterized by a particular activity state of the motorIautonomic and psychiclcognitive functional systems. S-W screening is possible through poly graphic monitoring of physiological variables and signals. Quantification of these signals introduces a set of parameters allowing the characterisation of the sleep (dys)function. There is no consensus regarding the choice or definition of these parameters. A particular cluster is presented and their informative value with respect to clinical practice and research is discussed.
