The effect of anodal transcranial direct current stimulation on multi-limb coordination performance.

Motor coordination is the combination of body movements performed in a well-planned and controlled manner based upon motor commands from the brain. Several interventions have been in practice to improve motor control. Transcranial direct current stimulation (tDCS) is getting a lot of attention these days for its effect in improving motor functions. Studies focusing on the ability of tDCS to improve motor control, inhibition and coordination are sparse. Therefore, the influence of tDCS stimulation at the right dorsolateral prefrontal cortex (DLPFC) on motor control and coordination was investigated, in a sham-controlled double-blinded pseudo-randomized design, with a multi-limb coordination task in healthy young subjects. Number of errors and reaction time were used as outcome parameters. Our findings showed that, anodal tDCS reduced the number of errors only in the heterolateral coordination condition, however there was no change in reaction time. No changes were found for the homolateral and three-limb coordination conditions.

Long-term TENS treatment decreases cortical motor representation in multiple sclerosis.

This study investigated the effects of a long-term transcutaneous electrical nerve stimulation (TENS) treatment on cortical motor representation in patients with multiple sclerosis (MS). In this double-blind crossover design, patients received either TENS or sham stimulation for 3 weeks (1h per day) on the median nerve region of the most impaired hand, followed by the other stimulation condition after a washout period of 6 months. Cortical motor representation was mapped using transcranial magnetic stimulation (TMS) at the baseline and after the 3-week stimulation protocol. Our results revealed that 3 weeks of daily stimulation with TENS significantly decreased the cortical motor representation of the stimulated muscle in MS patients. Although the mechanisms underlying this decrease remain unclear, our findings indicate that TENS has the ability to induce long-term reorganization in the motor cortex of MS patients.

Directional constraints during bimanual coordination: the interplay between intrinsic and extrinsic directions as revealed by head motions.

The role of directional compatibility was investigated during the production of in-phase and anti-phase coordination patterns involving both arms as well as the head. Our first aim was to compare the quality of coordination between both arms when symmetrical arm posture manipulations were used to disentangle muscle homology from the mutual direction of limb motions in extrinsic space. Findings revealed that in-phase coordination, characterized by the simultaneous activation of homologous muscle groups, was resistant to posture manipulations. Conversely, during anti-phase coordination, the influence of extrinsic direction became more prevalent whereby isodirectionality in extrinsic space contributed to stabilization of anti-phase coordination patterns. The second aim was to study the effect of periodic head movements upon the assembling of a coordinative synergy among the body segments. The findings demonstrated that the in-phase patterns were hardly affected by directionality of head motion. Conversely, the anti-phase patterns were more vulnerable to the directional influence of head movements, showing less accurate and stable coordination during non-isodirectional than isodirectional head motions. These observations underscore the robust nature of coordination patterns based on muscle homology, even in the absence of symmetric arm positions. Moreover, isodirectional head movements became easily integrated with the overall coordination pattern, whereas head-limb coupling was poor when the head moved anti-directional with the limbs.

The coalition of constraints during coordination of the ipsilateral and heterolateral limbs.

Previous work on the coordination between the upper and lower limbs has invariably shown that its accuracy/stability is primarily determined by the mutual direction between limbs in extrinsic space and not by muscle relationships. Here we show that muscle grouping does play a critical role in coordination of the arm and leg, in addition to direction. More specifically, the simultaneous activation of isofunctional muscles and/or limb movements proceeding in the same direction, results in more successful performance than the alternated activation of isofunctional muscles and/or movements occurring in different directions. In the absence of isofunctional muscle coupling, the mutual direction between the limbs plays a more prominent role in determining coordinative accuracy. These coordination constraints can largely account for the observed differences between ipsilateral and heterolateral limb coordination. The findings are discussed in view of the coalition of coordination constraints.

The role of directional compatibility in assembling coordination patterns involving the upper and lower limb girdles and the head.

The role of directional compatibility was investigated during the production of in-phase and anti-phase coordination patterns involving the four limbs as well as the head. Our first aim was to compare the quality of interlimb coordination between concordant and discordant coordination patterns across girdles at different cycling frequencies. Concordant implied adoption of either the in-phase or anti-phase coordination mode across both girdles whereas discordant implied a combination of both modes. The second aim was to study the effect of periodic head movements upon the assembling of a coordinative synergy among the limbs. Findings revealed that concordant coordination modes were produced with higher accuracy and consistency than discordant coordination modes and this effect was more distinct at higher cycling frequencies. Inclusion of head movements was found to destabilize in-phase coordination but stabilize anti-phase coordination patterns, particularly during discordant conditions at higher cycling frequencies. This observation contrasts with previous findings in which anti-phase modes have invariably been shown to be more vulnerable to experimental perturbations than in-phase modes. The findings are discussed within the context of the coalition of egocentric and allocentric constraints during multilimb coordination and the role of direction as an organizing principle in movement control.