Increased sensitivity of spatial filters by combining the magnetic and electrical components of the sensorimotor cortical beta rhythm

Abstract

Modulation of human magnetic or electrical sensorimotor rhythms during motor imagery is widely used in fundamental and applied neurophysiological research. To date, there is evidence of a better sensitivity of magnetic field sensors to beta-rhythm modulation, however, the potential synergistic effect of combining the two modalities has not yet been investigated. In this study, simultaneous registration of electroencephalogram (EEG) and magnetoencephalogram (MEG) was carried out in eight healthy volunteers during voluntary and imaginary movements, as well as during electrical stimulation of the median nerve. In all subjects, it was possible to identify desynchronization (suppression) of mu and beta rhythms during the performance of sensorimotor tasks, as well as beta synchronization after the end of movement or stimulation. Using the common projections of the covariance matrices of signals of the electric, magnetic, and combined (“MEEG”) modalities, the most sensitive individual spatial filters were calculated separately for each type of reaction. Relative to the pre-stimulus control, the changes in the amplitude of the sensorimotor rhythm components turned out to be the largest in the combined MEEG modality. At the same time, for mu-desynchronization, MEEG turned out to be significantly better than MEG, and for beta-desynchronization, MEEG turned out to be significantly better than both MEG and EEG. For beta synchronization, a shift in the position of sources in the fronto-medial direction was shown, and there were no significant differences in amplitude between modalities. It was also shown that for beta desynchronization, most subjects identified MEG sources with identical EEG projections or without pronounced EEG projections, which indicates the presence of several small tangentially located cortical dipoles involved in beta rhythm desynchronization. The results obtained indicate that in studies of modulation of sensorimotor rhythm components, in particular beta desynchronization, the combination of MEG and EEG leads to greater sensitivity. The multifocal nature of the magnetic beta rhythm and its varying severity in EEG sources indicate the presence of independent regulatory circuits of cortical-thalamic or intracortical origin.