Motor-related cortical dynamics to intact movements in tetraplegics as revealed by high-resolution EEG

We explored the cortical dynamics during movements of an unaffected body part in tetraplegic subjects with chronic spinal cord injury (SCI). The aims were to find out whether the intact movements were associated with a physiological time-varying pattern of activity in the motor-related cortical areas and whether the primary motor area (MI) activation followed a somatotopic distribution. Event-related potentials to self-initiated lip movements were analyzed by means of cortical source imaging of EEG recorded from seven tetraplegic subjects and seven control subjects. Regions of interest (ROIs) were selected on individual MRI and the time-varying electrophysiologic activity (cortical current density, CCD) was estimated on these ROIs and subjected to across-subject analysis. A significant, bilateral movement-related pattern of MI activation was detected during motor task execution in SCI patients as well as in controls. The site of local maxima activation displayed a symmetrical discrete distribution within MI, consistently with a putative somatotopic lip representation, in all the subjects. The supplementary motor area proper (SMAp) was always coactivated with MI and coactivation was characterized by a time course with typical premotion and motion phases over both motor areas. A clear-cut temporal delay between the SMAp and MI activation did not occur either in SCI patients or in controls. These findings obtained with noninvasive neuroelectrical source imaging document that in chronic SCI subjects "executive" motor areas are engaged with a preserved temporal and spatial pattern during preparation and execution of intact movements.