Facilitation of corticospinal excitability by virtual reality exercise following anodal transcranial direct current stimulation in healthy volunteers and subacute stroke subjects

Abstract

BackgroundThere is growing evidence that the combination of non-invasive brain stimulation and motor skill training is an effective new treatment option in neurorehabilitation. We investigated the beneficial effects of the application of transcranial direct current stimulation (tDCS) combined with virtual reality (VR) motor training.MethodsIn total, 15 healthy, right-handed volunteers and 15 patients with stroke in the subacute stage participated. Four different conditions (A: active wrist exercise, B: VR wrist exercise, C: VR wrist exercise following anodal tDCS (1 mV, 20 min) on the left (healthy volunteer) or affected (stroke patient) primary motor cortex, and D: anodal tDCS without exercise) were provided in random order on separate days. We compared during and post-exercise corticospinal excitability under different conditions in healthy volunteers (A, B, C, D) and stroke patients (B, C, D) by measuring the changes in amplitudes of motor evoked potentials in the extensor carpi radialis muscle, elicited with single-pulse transcranial magnetic stimulation. For statistical analyses, a linear mixed model for a repeated-measures covariance pattern model with unstructured covariance within groups (healthy or stroke groups) was used.ResultsThe VR wrist exercise (B) facilitated post-exercise corticospinal excitability more than the active wrist exercise (A) or anodal tDCS without exercise (D) in healthy volunteers. Moreover, the post-exercise corticospinal facilitation after tDCS and VR exercise (C) was greater and was sustained for 20 min after exercise versus the other conditions in healthy volunteers (A, B, D) and in subacute stroke patients (B, D).ConclusionsThe combined effect of VR motor training following tDCS was synergistic and short-term corticospinal facilitation was superior to the application of VR training, active motor training, or tDCS without exercise condition. These results support the concept of combining brain stimulation with VR motor training to promote recovery after a stroke.Electronic supplementary materialThe online version of this article (doi:10.1186/1743-0003-11-124) contains supplementary material, which is available to authorized users.

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“…Although time spent in therapy is an accepted metric of task‐practice intensity, there is a growing understanding that the number of repetitions performed in every session provides a more accurate measurement of intensity [53]. Only 1 study [44] explicitly mentioned the number of repetitions performed. However, it is currently unclear as to how many repetitions are necessary for optimal motor improvements in individuals with post‐stroke UL hemiparesis [54].…”

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“…Importantly, decreased mouse head volume compared to the rat suggests a further scaling factor – which if ≥ 2 brings this result in line with those in healthy rats. However, it is important to note that several studies in the acute and subacute phase of recovery have been successfully conducted in humans (see above) without reported serious adverse events [186], [152], [153], [187], [188]. …”

“…In studies of tDCS in persons with stroke, adults and children, published since 2014 (N=33 studies), there are 2 studies reporting minor adverse events [79], [152] including mild headache, sleepiness, and various sensations. In addition, there are few reports of dropouts with 14 from 6 studies [153], [79], [28], [154], [155], [156] out of 507 total participants across 33 studies.…”

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“…The most common reported AEs were mild sensory phenomena that only occurred during stimulation at or near the electrodes (tingling, itching, phosphenes) that occurred in 253 (11.2%) subjects (e.g., Grecco et al, 2014a; Triccas et al, 2015). Transient events included skin irritation (75 subjects; 3.3%, Ferrucci et al, 2014; Triccas et al, 2015), issues with sleep or energy level, including sleepiness, fatigue, and insomnia (74 subjects; 3.3%; e.g., Lesniak et al, 2014; Murray et al, 2015), headache or nausea (56 subjects; 2.5%; Khedr et al, 2014; Kim et al, 2014), problems with concentrating (15 subjects; 0.7%; e.g., Wrigley et al, 2013), and neck pain (4 subjects; 0.2%; e.g. Straudi et al, 2016).…”