Transcranial direct current stimulation (tDCS) and robotic practice in chronic stroke: the dimension of timing

Abstract

Background: Combining tDCS with robotic therapy is a new and promising form of neurorehabilitation after stroke, however the effectiveness of this approach is likely to be influenced by the relative timing of the brain stimulation and the therapy.

Objective: To measure the kinematic and neurophysiological effects of delivering tDCS before, during and after a single session of robotic motor practice (wrist extension).

Methods: We used a within-subjects repeated-measurement design in 12 chronic (>6 months) stroke survivors. Twenty minutes of anodal tDCS was delivered to the affected hemisphere before, during, or after a 20-minute session of robotic practice. Sham tDCS was also applied during motor practice. Robotic motor performance and corticomotor excitability, assessed through transcranial magnetic stimulation (TMS), were evaluated pre- and post-intervention.

Results: Movement speed was increased after motor training (sham tDCS) by ∼20%. Movement smoothness was improved when tDCS was delivered before motor practice (∼15%). TDCS delivered during practice did not offer any benefit, whereas it reduced speed when delivered after practice (∼10%). MEPs were present in ∼50% of patients at baseline; in these subjects motor practice increased corticomotor excitability to the trained muscle.

Conclusions: In a cohort of stroke survivors, motor performance kinematics improved when tDCS was delivered prior to robotic training, but not when delivered during or after training. The temporal relationship between non-invasive brain stimulation and neurorehabilitation is important in determining the efficacy and outcome of this combined therapy.

Fig. 1

20-minute motor practice paradigm showing: (a) the visual cue display on a monitor in front of the patient, full circle = current position, open circle = target, and (b) the patient moves the wrist to extension, and upon reaching the target, the robotic device returns the wrist to neutral. This is repeated at a rate of 1 movement per 5 seconds.

Fig. 2

Group normalized data for each of the experimental conditions, showing mean speed to be increased as a consequence of practice (left bar). When tDCS was delivered before practice, the increase in speed was substituted for enhanced movement smoothness. With tDCS delivered during practice or after practice (the two right-hand bars), there was no improvement in performance. Aim worsened (tDCS during) and speed slowed (tDCS post), suggesting a non-beneficial effect with tDCS delivered at these time points.