Chaotic time series analyses of epileptic seizures

A number of seizure events, typical of everyday clinical practice, were tested for possible chaos. After a careful elimination of spurious effects, evidence of chaos was found in two seizure events. This was confirmed by direct examination of exponential separation of initially nearby states in low-dimensional trajectory recoveries. The resulting Lyapunov exponent calculation provides a clear indication of chaos in such events, the definitive conclusion of which cannot be made from dimension calculations alone. The weakness of these techniques, and strategies for their treatment, are emphasized.