Transcranial direct current stimulation assists chronic stroke rehabilitation

By Eleanor McDermid

Adding ipsilesional anodal transcranial direct current stimulation (tDCS) to upper limb rehabilitation delivers motor improvements in chronic stroke patients that last for at least 3 months, a randomised trial shows.

The small trial, published in Science Translational Medicine, involved 24 patients who had experienced a stroke at least 6 months previously, leaving them with impaired motor function in the contralateral hand.

These patients undertook the Graded Repetitive Arm Supplementary Program for 1 hour per day over 9 days. For the first 20 minutes of each session they also received real or sham tDCS.

At 3 months after the intervention, impairment and activity had improved in all patients, but by significantly more among the 11 patients in the tDCS group than the 13 in the control group.

Further analysis showed that their scores for activity had improved significantly more, by 5.763 points for the Action Research Arm Test and 6.871 points for the Wolf Motor Function Test, but the change in their impairment scores on the Upper Extremity Fugl-Meyer Assessment had not.

"Our findings therefore suggest that anodal tDCS to the ipsilesional hemisphere may exert its effects by enhancing activity and reducing functional limitations, rather than by changing the impairment", write Heidi Johansen-Berg (John Radcliffe Hospital, Oxford, UK) and co-workers.

They note that activity improvement may be thought of as compensation rather true recovery, but stress that "even compensation can be useful to patients if it allows them to perform movement tasks more effectively than before."

And they add that identifying the means of improvement is important for understanding "how best to use tDCS in stroke rehabilitation."

Functional magnetic resonance imaging revealed that the improvements in the tDCS group were associated with increased activation of brain regions including parts of the ipsilesional motor cortex during passive movement of the affected hand. There were also increases in grey matter volume in the ipsilesional premotor cortex and primary motor cortex and the contralesional postcentral gyrus.

Although corticospinal tract asymmetry on fractional anisotropy did not change more in the tDCS than sham group, the team found that greater asymmetry at baseline was associated with worse motor function.

Together this suggests "that the condition of residual brain pathways [...] may place some constraints on motor ability", they say, but that "further gains in function may be possible and are more strongly associated with altered activation of motor cortical areas and gray matter structural changes, rather than with changes in white matter connectivity."

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