Effects of combined peripheral nerve stimulation and brain polarization on performance of a motor sequence task after chronic stroke

Abstract

Background and purpose: Recent work demonstrated that application of peripheral nerve and cortical stimulation independently can induce modest improvements in motor performance in patients with stroke. The purpose of this study was to test the hypothesis that combining peripheral nerve stimulation (PNS) to the paretic hand with anodal direct current stimulation (tDCS) to the ipsilesional primary motor cortex (M1) would facilitate beneficial effects of motor training more than each intervention alone or sham (tDCS(Sham) and PNS(Sham)).

Methods: Nine chronic stroke patients completed a blinded crossover designed study. In separate sessions, we investigated the effects of single applications of PNS+tDCS, PNS+tDCS(Sham), tDCS+PNS(Sham), and PNS(Sham)+tDCS(Sham) before motor training on the ability to perform finger motor sequences with the paretic hand.

Results: PNS+tDCS resulted in a 41.3% improvement in the number of correct key presses relative to PNS(Sham)+tDCS(Sham), 15.4% relative to PNS+tDCS(Sham), and 22.7% relative to tDCS+PNS(Sham). These performance differences were maintained 1 and 6 days after the end of the training.

Conclusions: These results indicate that combining PNS with tDCS can facilitate the beneficial effects of training on motor performance beyond levels reached with each intervention alone, a finding of relevance for the neurorehabilitation of motor impairments after stroke.

Figures

Fig. 1

Experimental design. Patients participated in 4 sessions (order randomized across subjects): PNSSham+tDCSSham, PNS+tDCSSham, tDCS+PNSSham and PNS+tDCS (see text for details). Each session started with 3mins baseline measurement (Base) of performance of a finger sequence task followed by each form of stimulation (2hrs of PNS or Sham, combined with 20min of tDCS or Sham). Each form of stimulation preceded 5 identical blocks of 3mins motor sequence practice performed with 2mins break between blocks. Training was followed by 30mins break after which post training measurements were obtained on Day 1, Day 2 and Day 6 (6.3±0.5 days). Questionnaires (Q) where patients reported the level of attention, fatigue, hand tiredness and perceived difficulty to each sequence were obtained using separate visual analogue scales at four different time points in each session. Inset shows the number of correct key presses for one subject during each 30secs epoch. The mean number of correct key presses per 30secs during the 2nd, 3rd and 4th 30secs epochs (dark grey area) was used to calculate the primary outcome measure (see text).

Fig. 2

The graph shows the mean number of correct key presses per 30sec at baseline and during finger sequence practice after each stimulation condition (shaded area, mean/SEM). Note the comparable baseline values and the overlapping training-dependent improvements across interventions.

Fig. 3

The bar graph shows the effects of the different interventions on the % change in correct key presses per 30secs relative to baseline (dotted line, 100%). Note that on Day 1, PNS+tDCS was significantly better than PNSSham+tDCSSham. This effect was more pronounced at Day 2 when PNS+tDCS elicited significantly more gains than PNSSham+tDCSSham, PNS+tDCSSham or tDCS+PNSSham (black arrows) and partially present by Day 6. The inset graph shows individual patients’ change in correct key presses relative to baseline between PNSSham+tDCSSham, PNS+tDCSSham, tDCS+PNSSham and PNS+tDCS at Day 2. Values represent mean±SEM; *p < 0.05, **p < 0.01.