METHOHEXITAL-INDUCED CHANGES IN SPECTRAL POWER OF NEUROMAGNETIC SIGNALS - BETA-AUGMENTATION IS SMALLER OVER THE HEMISPHERE CONTAINING THE EPILEPTOGENIC FOCUS

Previous research has suggested that methohexital, a short-term barbit urate, alters activity in the primary epileptogenic area. It can be as sumed that drug-induced activation of the epileptogenic focus provides a rapid and safe method to obtain a sufficient amount of information relevant for the lateralization and localisation of the primary epilep togenic area. This study shows that methohexital changes spectral powe r in the beta band derived from magnetoencephalographic (MEG) signals over the hemisphere ipsilateral to the primary epileptogenic area. Thi s effect was demonstrated for 10/13 of the investigated patients suffe ring from unilateral temporal lobe epilepsy (TLE). The side and locati on of the primary epileptogenic area of these patients (5 left TLE, 8 right TLE) was determined invasively during presurgical evaluation. Du ring a 1-2 minute interval after intravenous bolus injection of 100 mg methohexital a clear lateralization effect in the beta band was obser ved, which differed marginally between fronto-central, fronto-temporal and temporo-parietal brain regions. In addition, bilateral spectral p ower changes were obtained in the theta, alpha and gamma bands that di ffered between brain regions. Analyses of simultaneously recorded scal p electroencephalographic (EEG) data revealed effects consistent with those of the MEG analysis. The reduced enhancement of beta band spectr al power of MEG recordings provides a potential application for the no n-invasive lateralization of the primary epileptogenic area.