Why did you decide to undertake this review? Were there strong reasons to think that adding tDCS to walking training would be beneficial in Parkinson’s disease?

There is a growing clinical and research interest in the effects of non-invasive brain stimulation, such as tDCS, as an adjunct therapy in rehabilitation of people with neurological diseases.

On the other hand, there is still very little high-quality evidence to support or refute its clinical application.

It has been suggested that tDCS may enhance extracellular dopamine levels in the striatum and inhibit GABAergic neurons in Parkinson’s disease.

This would improve brain structure and function and the effects might be carried over to improve everyday activities such as walking.

Were there existing literature reviews on this topic already?

Previous literature reviews focused on the effects of tDCS alone or included studies not appropriate for examining the effects of intervention.

Our review included randomised clinical trials that examined the effects of the addition of tDCS to walking training in comparison with walking training alone (or combined with sham-tDCS).

In other words, this review investigated if the time and money spent in adding tDCS to walking training is worthwhile.

What outcomes did you consider in the review?

We planned to investigate the effects on walking, that is, speed, step length and number of steps per minute, as well as on freezing of gait, falls and social participation.

However, conclusions were only possible for the spatiotemporal outcomes related to walking.

How did the addition of tDCS to walking training affect walking speed, step length and cadence?

Meta-analysis based on five randomised trials indicated that the addition of tDCS to walking training produced no or negligible effects on walking spatiotemporal outcomes.

The mean difference between groups was close to zero and the 95 per cent confidence intervals included negative and positive values also close to zero.

This suggests that any plausible existing effect is not clinically relevant.

What about the other outcomes?

Unfortunately, no randomised trials examined the effects on those outcomes.

Because no effects were found on walking spatiotemporal parameters, it is unlikely that the addition of tDCS would help improve social participation.

On the other hand, effects on freezing of gait should be further explored.

Do you think this result could be influenced by further research on this topic?

Although the included trials had moderate to high methodological quality, the sample was small and the quality of the evidence was graded as moderate; this means that the true effect is likely to be close to the estimate of the effect, but larger trials might still change some estimates.

In addition, some trials included participants with mild walking limitations, which may give little room for improvement.

We are currently working on a triple-blind randomised trial examining the effects of 30 minutes of tDCS applied simultaneously to walking training in people with moderate walking limitations due to Parkinson’s disease.

I am thankful for the opportunity to discuss and share the results of our systematic review.

I also thank my colleagues and co-authors Willian do Carmo, Gabriela de Oliveira, Fernando Arêas and Fernanda Dias for their qualified work.

>> Lucas Rodrigues Nascimento is a physiotherapist, senior researcher and associate professor at the Center of Health Sciences, Universidade Federal do Espírito Santo, Brazil. He has a PhD degree in rehabilitation sciences from the University of Sydney (Australia) and Universidade Federal de Minas Gerais (Brazil) and his key research interests are neuroscience and neurological rehabilitation.