Common dynamics in temporal lobe seizures and absence seizures

Similarities among the clinical features of complex partial temporal lobe s eizures and absence (petit mal) seizures suggest shared underlying mechanis ms, bur dissimilar electrographic features of the two seizure types have ca st doubt on common neuronal substrates. However, visual inspection and trad itional approaches to quantitative analysis of the electroencephalogram and electrocorticogram, such as Fourier analysis, may not be appropriate to id entify and characterize the highly non-linear mechanisms likely to underlie ictal events. We previously introduced a technique. non-linear autoregress ive analysis, that is designed to identify non-linear dynamics in the elect roencephalogram [Schiff N. D. et al. (1991) Society of Neuroscience Neurosc ience 21st Annual Meeting, 638.6; Schiff N. D. et al. (1995) Biol. Cybern. 72, 519-526, 527-533]. The non-linear autoregressive analysis technique is aimed at describing seizure discharges as a disturbance of synchrony at the level of neuronal circuits. In absence seizures, we showed that non-linear autoregressive analysis revealed a consistent "fingerprint" of these non-l inearities in 3/s discharges within and across patients. Here, we investiga te the possibility that non-linear autoregressive modeling of seizure recor ds from patients with temporal lobe epilepsy might reveal common circuit me chanisms when compared with the non-linear autoregressive analysis fingerpr int of absence seizures. Electrocorticographic records of seizure activity were obtained in four patients who had received subdural grids or strips im planted in preparation for epilepsy surgery. Decomposition of the multichan nel data recorded from these patients by principal component analysis revea led that. at least three to five independent "generators" were required to model the data from each patient. Non-linear autoregressive analysis of the se extracted generators revealed non-linear dynamics in two patients. In bo th patients, the temporal aspects of these non-linearities were similar to the characteristic non-linearities identified in the non-linear autoregress ive analysis fingerprint of absence seizures. In particular, both patients showed a non-linear interaction of signals 90 ms in the past with signals 1 50 ms in the past. This was the most prominent interaction seen in all pati ents with absence seizures (typical and atypical). These results suggest that seizures from some patients with temporal lobe e pilepsy may share common underlying circuit mechanisms with those of absenc e seizures, Physiological interpretations of these results are considered a nd proposed mechanisms are placed into the context of the alterations of co nsciousness seen in both epilepsies. (C) 1999 IBRO. Published by Elsevier S cience Ltd.