A clinical improvement was seen in 43 % of patients in a minimally conscious state after tDCS. “In other words, these patients displayed signs of consciousness that had never previously been observed in them”, Steven Laureys explains. “We were even able to establish functional communication with two of them. We asked them six easy questions such as "Am I touching my nose?", and they replied correctly to each one, either by moving their head or blinking."

A predictive element

For Aurore Thibaut, the first author of the article(1) published on this work in the journal Neurology, "these results were all the more impressive since they occurred in chronic patients, i.e. years after their injury, whose condition is all too often considered as no longer being able to evolve." She adds: “On the contrary, our study shows that the state of consciousness of severely brain-damaged patients can progress following brief cortical stimulation. However, this improvement is only temporary and the patients return to their initial state after several hours."

Patients in a vegetative state/unresponsive wakefulness syndrome don’t benefit in any way from transcranial direct current stimulation. And while 43 % of the patients in a minimally conscious state show a temporary improvement, in 57 % there is no change at all. Why? Researchers from the Coma Science Group are currently trying to find an answer to this question. Aurore Thibaut has already provided some initial answers. By using positron emission tomography (PET scan), she demonstrated that the patients who responded to tDCS were those who have maintained metabolic activity in one of the regions targeted by the propagated current, i.e. the prefrontal left region. It would appear that the presence of this protected metabolic activity is a predictive element of the stimulation’s effectiveness. However, the molecular effects of tDCS still need to be clarified in order to unearth the inner workings.

And the long-term impact?

For the moment, the researchers from the Coma Science Group are studying the impact of repeated stimulation (20 minutes a day for a week) in patients in a minimally conscious state receptive to tDCS.  The goal is to prolong and maintain the benefits generated by this technique on cognitive and motor skills in the people concerned in the long term. “The ease of use and relatively low cost of this new technique makes it a good candidate for aftercare in daily clinical practice, in order to stimulate the recovery of patients who have survived a coma”, says Professor Laureys. He adds that it could also be useful to improve the evolution of patients plunged into a chronic minimally conscious state.

It was commonly thought that the brain lost all its plasticity beyond the acute phase of an altered state of consciousness. The work of the Coma Science Group underlines the fact that this is not the case, and that it maintains a certain plasticity for years. "However, we shouldn’t deduce from this that everything is possible", insists the head of the team in Liège. “The clinical reality is that there are patients who remain very handicapped. Consequently, our discovery doesn’t fundamentally reopen the debate on the end of life of patients in a chronic altered state of consciousness."

(1) Aurore Thibaut, Marie-Aurélie Bruno, Didier Ledoux, Athena Demertzi, Steven Laureys, tDCS in patients with disorders of consciousness: sham-controlled randomized double blind study, Neurology, 2014 Apr 1;82(13):1112-8.