Proceedings of The Physiological Society

Physiology 2012 (Edinburgh) (2012) Proc Physiol Soc 27, PC258

Poster Communications

Anodal transcranial direct current stimulation modifies development of a spatial motor skill in healthy adult humans

J. Ashworth-Beaumont1, A. Nowicky1

1. Centre for Rehabilitation Research, Brunel University London, Uxbridge, United Kingdom.

  • Figure 1: Effect of anodal tDCS intervention group allocation and task practise on spatial motor skill (TPR). Change in observed motor skill in training, relative to baseline (B) sample mean. Shaded areas: 2 day/48 hour rest between sessions 1 and 2; 7 day/168 hour rest between session 2 and follow-up (F). *Significant difference independent t-test p≤0.05, the net effect of task experience and retention between ACTIVE (squares) and SHAM (diamond) groups at start of session 2.

Anodal transcranial direct current stimulation (tDCS) is a safe, non-invasive means of increasing the excitability of brain regions, with potential applications in neurorehabilitation of movement (1). Spatial accuracy, though essential in prehension (2) has not been fully integrated in previous skill measures. This study explores the effect of anodal tDCS on task learning and retention in a novel paradigm incorporating temporal and spatial dimensions as a univariate skill measure. 24 healthy right-handed adult volunteers were included in an RCT experimental format. All were trained in a novel sequential motor task requiring rapid, accurate peg transfer to raised targets using the non-dominant upper limb, over two 45 minute sessions spaced 48 hours apart. Adjunctive ACTIVE anodal tDCS (n=12, 1.5mA, 43μA/cm2) or a SHAM condition (n=12) was applied to the scalp overlying contralateral primary motor cortex (M1) during the first 20 minutes of practise. All attended for follow-up measurements after a further 7 days. The behavioural Task Productivity Rate (TPR) skill measure is a function of mean time required to achieve a standard spatial goal. For evaluation of focal M1 corticomotor plasticity related to task learning, measures were evoked using Transcranial Magnetic Stimulation (TMS)(3). Responses were gathered as surface EMG from the medial deltoid (mDelt), a shoulder muscle important in reaching and abductor pollicus brevis (APB), a vital muscle in grasp, analysed as stimulus-response characteristics (SRc). Analysis by ANOVA and student's t-test, values quoted mean±SEM. While task completion times were reduced under ACTIVE anodal tDCS stimulation through to a maximum difference 5.0±3.5% n.s. at the follow-up session compared to SHAM, skilled performance was significantly better in the SHAM group at the start of the second session by 10.6±5.0% p<0.05, effect size r=0.416 (Figure 1), which was not present at follow-up. Group-specific TMS response enhancements compared to baseline were found following training and persisted at follow-up in resting APB SRc p<0.05 in favour of the SHAM group but active mDelt SRc p<0.05 in favour of the ACTIVE group. In summary, ACTIVE application of anodal tDCS to M1 was associated with lasting plasticity in brain areas projecting to the shoulder muscle. Conversely, more rapid skill learning and retention with superior lasting cortical plasticity in the hand muscle representation was found under the SHAM condition. In a spatial accuracy task anodal tDCS modified skill learning and retention behaviour in a systematic and lasting fashion. The observed effect may be rooted in action prediction (4) with a secondary impact on task learning. The net clinical benefits of anodal tDCS on practical rehabilitation activities in patient groups may therefore emerge over longer timescales than previously considered.

Where applicable, experiments conform with Society ethical requirements