INTERMITTENCY AND PERIOD DOUBLING AS DYNAMICAL REGIMES IN EPILEPTIFORM ACTIVITY

Jose L. Perez Velazquez¹, Miguel A. Cortez¹, O. Carter Snead III¹, Richard Wennberg^2
1Division of Neurology, The Brain and Behavior Programme, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X87
²Division of Neurology, Toronto Western Hospital, 399 Bathurst Street, Toronto, Ontario, Canada

INTRODUCTION

We have identified two dynamical regimes during the transition to seizure and during the ictal events, using nonlinear dynamical systems theory.

METHODS

Human EEG recordings were performed with depth or subdural electrodes in 3 patients with temporal or frontal lobe epilepsy.  AY9944-induced atypical absence seizures were used to detect peaks  and interpeak interval (IPI) plots were constructed and analysed.

RESULTS

First return IPI plots revealed that the transition to seizure, the pre-ictal state, can be approximated by a one-dimensional mapping function that indicates that a flip or subharmonic bifurcation in the dynamics can occur. This bifurcation leads to type III intermittency or the period doubling cascade. Bifurcation analysis using the map parameters revealed periodic, quasiperiodic and possibly chaotic regimes. We find these dynamical regimes obtained from the analysis of the mapping function in recordings from 3 patients with intractable temporal or frontal lobe seizures, and in recordings from rats with atypical absence seizures or status epilepticus.

DISCUSSION

The pre-ictal and ictal activity display characteristics of intermittency and period doubling.  Specifically, the flip bifurcation  leads to the transient stabilization of a metastable steady state representing high-frequency hypersynchronous neuronal firing. The similarity in the dynamical regimes in the human and rat recordings suggest that similar collective dynamics are operating in the generation of seizures.