Structural Neural Correlates of Physiological Mirror Activity During Isometric Contractions of Non-Dominant Hand Muscles

Mirror Activity (MA) describes involuntarily occurring muscular activity in contralateral homologous limbs during unilateral movements. This phenomenon has not only been reported in patients with neurological disorders (i.e. Mirror Movements) but has also been observed in healthy adults referred to as physiological Mirror Activity (pMA). However, despite recent hypotheses, the underlying neural mechanisms and structural correlates of pMA still remain insufficiently described. We investigated the structural correlates of pMA during isometric contractions of hand muscles with increasing force demands on a whole-brain level by means of voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS). We found significant negative correlations between individual tendencies to display pMA and grey matter volume (GMV) in the right anterior cingulate cortex (ACC) as well as fractional anisotropy (FA) of white matter (WM) tracts of left precuneus (PrC) during left (non-dominant) hand contractions. No significant structural associations for contractions of the right hand were found. Here we extend previously reported functional associations between ACC/PrC and the inhibtion of intrinsically favoured mirror-symmetrical movement tendencies to an underlying structural level. We provide novel evidence that the individual structural state of higher order motor/executive areas upstream of primary/secondary motor areas might contribute to the phenomen of pMA.