The epileptic process as nonlinear deterministic dynamics in a stochastic environment: an evaluation on mesial temporal lobe epilepsy

The theory of deterministic chaos addresses simple deterministic dynamics i n which nonlinearity gives rise to complex temporal behavior. Although biol ogical neuronal networks such as the brain are highly complicated, a number of studies provide growing evidence that nonlinear time series analysis of brain electrical activity in patients with epilepsy is capable of providin g potentially useful diagnostic information. In the present study, this ana lysis framework was extended by introducing a new measure xi, designed to d iscriminate between nonlinear deterministic and linear stochastic dynamics. For the evaluation of its discriminative power, xi was extracted from intr acranial multi-channel EEGs recorded during the interictal state in 25 pati ents with unilateral mesial temporal lobe epilepsy. Strong indications of n onlinear determinism were found in recordings from within the epileptogenic zone, while EEG signals from other sites mainly resembled linear stochasti c dynamics. In all investigated cases, this differentiation allowed to retr ospectively determine the side of the epileptogenic zone in full agreement with results of the presurgical workup. (C) 2001 Elsevier Science B.V. All rights reserved.