Focal slow and beta brain activity in patients with multiple sclerosis revealed by magnetoencephalography

In multiple sclerosis (MS) inflammatory infiltrations cause white matter le sions. Magnetoencephalography (MEG) offers the opportunity to localize abno rmal electric activity of neurons with a high spatio-temporal resolution. I n this study, we investigated patients with MS in order to find if abnormal cortical activity is associated with (subcortical) MS lesions using simult aneous bilateral recording of biomagnetic activity. Eight patients sufferin g from definite laboratory-supported MS with mainly somatosensory deficits and multiple bihemispheric plaques revealed by MRI were included in the stu dy. To obtain normative data, 8 healthy volunteers were investigated follow ing the same measuring protocol. Spontaneous magnetic brain activity was re corded using a 2x37-channel biomagnetic system (BTI, USA). Offline analysis included digital filtering (to separately investigate slow and beta wave a ctivity), a Principle Component Analysis and the Dipole Density Plot. Local ization results were inserted into MR images using our contour fit procedur e. The dipole distribution in the brain was quantified and compared between the groups by statistical analysis. In all MS patients, the maximum of foc al abnormal activity was localized in cortical areas adjacent to the fiber lesions. In the healthy subjects, no focal abnormal brain activity could be found. However, the standardized maximum concentrations of dipoles were si gnificantly higher in the MS patients than in the healthy control group bot h in the slow and in the beta wave analysis. These results let assume that subcortical lesions can occur together with abnormal cortical neuronal acti vity. The results are discussed in respect to their impact on the interpret ation of the analysis of spontaneous magnetic brain activity.