Neuromagnetic fields accompanying unilateral finger movements: pre-movement and movement-evoked fields

Abstract

Neuromagnetic fields accompanying voluntary flexions of the right index finger were studied in five subjects. In all subjects, slow magnetic fields were observed over the central scalp beginning about 1 second prior to movement onset. These fields displayed a similar time course to the electrically recorded "readiness potential", but with reversals of field direction over regions of the rolandic fissure over both hemispheres. Least-squares fitting of two current dipole sources for the pre-movement fields resulted in a consistent localization of one source in the region of the rolandic fissure contralateral to the side of movement in four subjects. Ipsilateral dipole sources fitted inconsistently at deeper locations or outside the head indicating the inability of a single dipole source to account for the ipsilateral fields. A large field reversal was also observed over the contralateral (left) hemisphere, 90-130 ms after onset of EMG activity in the active muscles. In some subjects, single dipole sources could be fitted to this "movement-evoked" field at locations slightly deeper and posterior to the pre-movement source locations in the contralateral hemisphere, possibly indicating unilateral activation of somatosensory cortex related to sensory feedback during the onset of this movement. Subtraction of pre-movement field activity from post-movement fields improved the ability to fit a single contralateral rolandic source for all subjects suggesting that pre-movement sources continue to be active during movement onset. These findings confirm previous reports that voluntary finger movements are preceded by slow magnetic fields.(ABSTRACT TRUNCATED AT 250 WORDS)

The magnetic counterpart of the contingent negative variation

“…This would also be true for the terminal (late) CMV if we assume, for instance, that two bilateral sources in the motor cortex overlap. Two bilateral generators have been suggested in studies of the Bereitschaftsfield (motor field) prior to unilateral movement, e.g., by Cheyne and Weinberg (1989) and by Kristeva et al (1991). Such findings do not support an exclusively frontal location of the late CMV, as suggested by Fiumara et al (1985) or Fenwick et al (1992).…”

Involuntary Motor Activity in Pianists Evoked by Music Perception

“…Lang et al (1991) and Cheyne and Weinberg (1989) explain the failure of MEG to detect SMA as a possible generator of the early readiness potential prior to voluntary movements by the fact that several studies in primates (using single-cell recordings) and humans (using PET) have revealed that the SMA is bilaterally active even in unilateral movements. The activity of the SMA in both hemispheres can be described by two tangential dipoles that are antiparallel to each other and therefore do not produce an external magnetic field.…”

Movement-related cortical activation with voluntary pinch task: simultaneous monitoring of near-infrared spectroscopy signals and movement-related cortical potentials

“…15 According to previous MRCP study with MEG, 18 the motor field that peaks at EMG onset is present in the bilateral primary motor areas with contralateral dominance, and the movement-evoked field I, which is detected about 0.1 s after EMG onset, is present only in the contralateral somatosensory area. Since both are thought to be counterparts of the MP component of MRCP, 19 the MP component in C3 can be regarded as regional potentials mainly in the contralateral SMC.…”