Source modelling of the rolandic focus.

In rolandic epilepsy, consideration of the stereotyped ictal symptomatology suggests that the epileptic zone is likely to be in the same cortical structure in different patients. Routine EEG tracings of the interictal spike activity suggests a deep Sylvian fissure location. On the basis of the predominantly tangential potential field at the peak spike negativity seen in this group of patients, the inferior bank of the Sylvian fissure appears to be a good candidate. Without invasive studies, little refinement to this rather imprecise localization can be made as there is neither neurologic deficit nor lesion to provide a marker on radiological imaging. However, the application of source modelling technique using a simple single-dipole spherical head model has resulted in improved understanding of the generator behaviour, and facilitated the generation of new ways of analyzing spikes (e.g., stability index). Review of newer quantitative approaches including matrix and singular value decomposition of the dataset, spatial-temporal constrained source estimates etc. suggest other fruitful approaches. At least in some patients with partial epilepsy, the source characteristics of interictal scalp spikes appear to contain information of the ictal generator. Under certain circumstances, such derived information which is not otherwise available from routine electrophysiology may influence clinical management and prognosis. This is an additional bonus to the primary objectives of quantification and data reduction.