Neuromagnetic recordings in temporal lobe epilepsy

The introduction of whole-head magnetoencephalography (MEG) systems facilit ating simultaneous recording from the entire brain surface has established MEG as a clinically feasible method for the evaluation of patients with tem poral lobe epilepsy (TLE). In mesial TLE, two types of MEG spike dipoles co uld be identified. an anterior vertical and an anterior horizontal dipole. Dipole orientations can be used to attribute spike activity to temporal lob e subcompartments. Whereas the anterior vertical dipole is compatible with epileptic activity in the mediobasal temporal lobe, the anterior horizontal dipole can be explained by epileptic activity of the temporal tip cortex. In nonlesional TLE, medial and lateral vertical dipoles were found which co uld distinguish between medial and lateral temporal seizure onset zones as evidenced from invasive recordings. In lesional TLE, MEG could clarify the spatial relationship of the structural lesion to the irritative zone. Evalu ation of patients with persistent seizures after epilepsy surgery may repre sent another clinical important application of MEG because magnetic fields are less influenced than electric fields by the prior operation. Simultaneo us MEG and invasive EEG recordings indicate that epileptic activity restric ted to mesial temporal structures cannot reliably be detected on MEG and th at an extended cortical area of at least 6 to 8 cm(2) involving also the ba sal temporal lobe is necessary to produce a reproducible MEG signal. In lat eral neocortical TLE MEG seems to be more sensitive than scalp-EEG which fu rther underlines the potential role of MEG for the study of nonlesional TLE . Whole-head MEG therefore can be regarded as a valuable and clinically rel evant noninvasive method for the evaluation of patients with TLE.