CHARACTERIZING NONLINEARITY IN INVASIVE EEG RECORDINGS FROM TEMPORAL-LOBE EPILEPSY

Invasive electroencephalographic (EEG) recordings from depth and subdu ral electrodes, performed in eight patients with temporal lobe epileps y, are analyzed using a variety of nonlinear techniques. A surrogate d ata technique is used to find strong evidence for nonlinearities in ep ileptogenic regions of the brain. Most of these nonlinearities are cha racterized as ''spiking'' by a wavelet analysis. A small fraction of t he nonlinearities are characterized as ''recurrent'' by a nonlinear pr ediction algorithm. Recurrent activity is found to occur in spatio-tem poral patterns related to the location of the epileptogenic focus. Res idual delay maps, used to characterize ''lag-one nonlinearity'', are r emarkably stationary for a given electrode, and exhibit striking varia tions among electrodes. The clinical and theoretical implications of t hese results are discussed.