Template Analysis on Interictal Neuromagnetic Data from Cases of Focal and Generalized Epilepsy

The investigation of partial (focal) epilepsy by neuromagnetic measurements has provided significant results on the localization of epileptogenic foci related to intercritical activity (Barth et al., 1982; Chapman et al., 1983; Barth et al., 1984; Ricci et al., 1985). It has been demonstrated, however, that quite often the morphology of epileptic signals is not unique (Rose et al., 1987). This may be interpreted in terms of various neural groups simultaneously active but underlying different firing process. If we do not consider quasi-rhythmic activity, for which the best analytical approach remains the Relative Covariance Method (RCM) (Chapman et al., 1983), it would be particularly useful to identify a procedure that permits to reliably select epileptic signals (spikes, sharp waves, spike-and-wave complexes), and to eventually carry out a source localization procedure from the magnetic field distribution over the scalp relative to each of the selected epileptiform signals, henceforth referred to as epileptic complexes. An automatic selection procedure would be of great help also in the investigation of more complex diseases like, for instance, generalized epilepsy. In these pathologies the lack of simultaneity, which so far characterizes all neuromagnetic measurements, even those carried out with the largest systems today available, is one crucial drawback, the other being the variety of different signals that are usually recorded also during intercritical periods. For these reasons, the neuromagnetic study of cases of generalized epilepsy has been so far limited to simple morphological approaches, with no attempt to carry out source localization. with the unique exception of a recently reported study (Ricci et al., 1988) of photoconvulsive response, which may be referred to as one possible manifestation of generalized epilepsy (Jeavons and Harding, 1975).