Transcranial direct current stimulation of the supplementary motor area enhances intra-limb anticipatory postural adjustments

It has been recently demonstrated that alterations in anticipatory postural adjustments (APAs), which represent a fundamental component of any correct voluntary movement, contribute to the motor impairment after stroke. APAs circuitry is not fully understood, but several studies suggest that the supplementary motor area (SMA) is deeply involved. To confirm its involvement in APA generation, and verify the possibility to interfere with the latter, we applied trascranial direct current stimulation (tDCs) over the SMA, looking for effects on the postural control of the upper-limb during a simple index-finger flexion. Indeed, as shown in our lab (Caronni and Cavallari, Exp Brain Res 194:59,2009), finger flexion is preceded by inhibitory APAs carved in Biceps and Anterior Deltoid EMG, and by an excitatory APA appearing on Triceps EMG. Subjects (n=12) performed 3 sessions of 30 brisk flexions of the index-finger, while sitting on a chair with the right upper-arm along the body, elbow at 90° and hand prone. Before each session, subjects underwent tDCs (1mA, 20min) with CATHODAL, ANODAL or SHAM configuration. During ANODAL stimulation the average APAs in Biceps and Triceps were greater than during SHAM (BB: +26.5%, TB: +66%) and CATHODAL (BB: +20.5%, TB: +63.4%) stimulation (for both muscles, ANOVA p<0.02 Tukey p<0.05). Instead, the APA recorded on Anterior Deltoid was unchanged in all sessions. These results confirm the SMA involvement in APA generation and suggest that tDCs, which has been shown to be a valuable tool for treating different neurological conditions, may be as well employed for postural rehabilitation.