Tonic Motor Cortex Activation during Finger Movements Analyzed by Simultaneous DC Magnetoencephalography and DC Electroencephalography

Functional neuroimaging studies showed a linearly stronger motor cortex activation with increasing rates of repetitive finger movements. During very fast movements this correlation is abolished probably because of automation. Methodologically, these studies visualize neuronal activation indirectly via concomitant vascular/metabolic changes. In a complementary approach, DC magnetoencephalography (DC-MEG) as well as DC electroencephalography (DC-EEG) measure slow neuronal activation dynamics directly. Here, simultaneous DC-MEG and DC-EEG were used to characterize cortical neuronal activation during repetitive finger movements. 7 healthy subjects performed self-paced right finger movements. Alternating periods of 30s fast or slow finger movements, always separated by 30s rest periods, were performed over 30min. To prevent automation the subjects bent alternately the second and third finger twice. DC-MEG fields were recorded over the left hemisphere using a modulation-based MEG technique. DC-EEG potentials were registered using a custom-made DC amplifier with 16 electrodes clustered around C3. In 6/7 subjects fast and slow finger movements revealed motor-related DC-MEG and DC-EEG signals clearly above noise level. Fast finger movements revealed statistically significant stronger magnetic field amplitudes and electric potentials when compared with slow movements: (mean magnetic field strength: 179 fT vs. 155 fT; t-test: p<0.05; mean electric amplitudes: 15µV vs. 12µV; t-test: p<0.05). Notably, DC-MEG activity as well as DC-EEG activity showed a slow decay after the end of the movement, whereas DC-EEG time curves were somewhat prolonged when compared to the DC-MEG. In conclusion, this study demonstrates that DC-MEG combined with DC-EEG can provide a non-invasive neurophysiological reference for the interpretation of neuroimaging results even in long-lasting, tonic neuronal activation paradigms. In the exemplary simple finger movement paradigm, stronger cortical activation during fast, non-automatized finger movements in comparison to slow movements was demonstrated.