Electroencephalographic vigilance dynamics in multiple sclerosis during an acute episode and after remission

Twenty-three patients with multiple sclerosis were studied during an acute episode and again 4 weeks later. Whereas the patients' clinical condition improved significantly (Kurtzke DSS: from 3.9 (SD 1.4) to 3.3 (SD 1.5), P less than 0.001), the conventional power spectra of the resting EEG showed no marked changes. Following a 10-min EEG recording under resting conditions the patients performed a visuomotor tracking task, during which a further EEG recording was made. The frequency of the subvigilant non-A epochs of Loomis et al. as calculated for each minute of the resting recording was taken as the basis for evaluating the EEG dynamics of vigilance. A comparison during and after relapse showed differences in the time courses of the numbers of non-A epochs. While the non-A epochs were not time dependent in the acute phase, remission was characterized by a steady increase in non-A epochs across the 10 min of the recording period. This change in the dynamics of vigilance, which approximates a physiological pattern, was accompanied by an improvement in visuomotor tracking performance. Comparison of the power spectra of the EEG recorded during the tracking task showed a bifrontal increase in absolute alpha power during remission.