Motor performance improvements following tDCS and skill practice in older adults: Implications for motor skill training

Introduction: Neural degeneration accompanies healthy ageing, reducing the ability to perform activities of daily living. Transcranial direct current stimulation (tDCS) is an emerging technique with the potential to alter neuronal excitability. Although mechanisms of tDCS have been described, limited studies have examined whether tDCS can enhance performance benefits of motor skill training. Moreover, the most effective electrode montage to improve motor performance in older adults has not been explored. Objectives: The current study compared the effects of unilateral and bilateral tDCS combined with one session of skill practice, on corticospinal excitability, short-interval intracortical inhibition (SICI) and motor performance of the non-dominant limb in older adults. Materials and methods: In a double blinded cross-over design, nine participants (age 55–85 yrs.) underwent 15 min of unilateral, bilateral or sham tDCS (1 mA) combined with five minutes of vise108 Society Proceedings / Clinical Neurophysiology 124 (2013) e39–e187 uomotor tracking of the wrist. In all three conditions, the anode was positioned over the optimal site for the non-dominant extensor carpi radialis longus muscle. The order of conditions were counterbalanced and separated by a one week wash out. Transcranial magnetic stimulation and visuomotor tracking error assessed neurological function and motor performance at baseline, immediately after and 30 min following the cessation of stimulation. Results: Unilateral and bilateral tDCS improved visoumotor tracking error relative to sham, immediately post (15% & 21% respectively) and at 30 min following stimulation (both p < 0.05; 14% & 22%). In the corresponding non-dominant hemisphere, MEPs were elevated immediately post for sham, unilateral and bilateral conditions (all p < 0.05; 13%, 42% & 57%), however were only elevated at 30 min in unilateral and bilateral conditions (both p < 0.05; 59% & 56%). Both unilateral and bilateral tDCS facilitated MEPs relative to the sham condition at both time points (p < 0.05). SICI was reduced in both unilateral and bilateral conditions relative to sham, immediately post (29% & 37%) and at 30 min (both <0.05; 21% & 30%). For all variables (visuomotor tracking, MEPs and SICI), no differences between unilateral and bilateral tDCS were observed. Finally, bilateral tDCS suppressed MEPs in the dominant hemisphere immediately post (12%) and 30 min (14%) following tDCS (p < 0.05), however had no effect on SICI. Conclusions: Unilateral and bilateral tDCS modulated elements of cortical plasticity, irrespective of the electrode montage. These changes outlasted the stimulation period with subsequent changes in motor performance, relative to motor practice alone. These findings provide preliminary evidence for tDCS to preserve or improve motor control in the elderly.