[Contribution of non-linear mathematics (chaos theory) to EEG analysis]

Since 1963, nonlinear dynamics or "chaos theory" were widely used in various area of physics. The first application to the analysis of the human electroencephalogram (EEG) was performed in 1985. A tutorial revue of some concepts of nonlinear dynamics is presented with the various results obtained since 1985. The dimensional complexity of the EEG (DC) seems a good descriptor of the "desynchronisation" or decorrelation of the EEG: DC is high with eyes open, during a mental task and also during a tonic epileptic discharge. DC is low with eyes closed, during slow wave sleep, and during a clonic epileptic discharge. The measure of DC could allow a more objective comparison between various states of electrical cerebral activity.