Transcranial Stimulation in Disorders of Consciousness

Pauline Anderson

April 03, 2014

Transcranial direct-current stimulation (tDCS) could offer short-term benefits to some patients with disorders of consciousness (DOCs) subsequent to severe brain damage, a new study has shown.

Researchers are reporting that a single session of anodal tDCS applied to the left dorsolateral prefrontal cortex improved scores on a coma recovery scale in some patients in a minimally conscious state (MCS), without causing adverse effects.

The study included 30 patients in an MCS who showed reproducible but inconsistent signs of consciousness and 25 patients in a vegetative state/unresponsive wakefulness syndrome (VS/UWS), who showed only reflex movements. Causes of brain injury included trauma, anoxia, cerebrovascular accident, and subarachnoid hemorrhage.

"Our study illustrates the residual capacity for neural plasticity and temporary recovery of (minimal) signs of consciousness in some patients in MCS, but does not permit to make any claims regarding possible long-term tDCS effects," the researchers, with senior author Steven Laureys, MD, PhD, from the Coma Science Group, Cyclotron Research Center, and the Departments of Neurology and General Intensive Care at University Hospital of Liège, Belgium, write.

Their findings were published in the April 1 issue of Neurology.

Short Session

Each patient received one 20-minute session of both active tDCS and sham stimulation. tDCS is a form of noninvasive cortical stimulation that modulates cortical excitability at stimulation sites via weak polarizing currents.

The stimulation device included a build-in placebo mode. Both patients and administrator were blinded to whether the stimulation was a sham or actual treatment.

To assess tDCS treatment effects, researchers used the Coma Recovery Scale-Revised, which consists of 23 items that address auditory, visual, motor, verbal, communication, and arousal functions. Scoring is based on the presence or absence of specific behavioral responses to sensory stimuli administered in a standardized manner.

The study found that 43% of patients in an MCS (13 of 30) had a tDCS-related improvement in that they showed a clinical sign of consciousness not seen before. In the MCS group, the difference in total score change between tDCS and sham was 1.6 (P = .003).

Of the 13 patients in an MCS who responded, 5 had sustained their brain injury more than a year before the study. "These clinical improvements in long-standing MCS corroborate previous evidence for late recovery and neural plasticity in MCS," said the authors.

They note that 2 patients in the MCS group were receiving amantadine, but the treatment was started 6 months before study inclusion and remained unchanged during the experiment.

The authors hypothesize that the treatment may have enhanced attention and working memory processes that underlie many conscious tasks.

In the VS/UWS group, 2 acute (less than 3 months) patients (8%) showed tDCS-related signs of consciousness that weren't observed during the pretreatment evaluation or during the pre- or post-sham evaluation.

There were no treatment-related adverse effects.

The tDCS stimulation may have some advantages over repetitive transcranial magnetic stimulation (rTMS), which induces neuronal firing in the stimulated location. It's easier to apply, causes less discomfort, and has a lower risk of inducing seizures, said the authors.

A limitation of the study was that it didn't include MRI-based mapping of the stimulated area.

Promising Site

Writing in an accompanying editorial, John Whyte, MD, PhD, Moss Rehabilitation Institute, Elkins Park, Pennsylvania, said the new study is "of considerable interest" as it points to "another potential treatment avenue for DOC as well as a promising site of intervention."

However, said Dr. Whyte, to generate a clinically useful intervention, the treatment will need "a translational research process" that would involve both scientific and practical obstacles.

"First, of course, is the need to determine whether these short-term effects can be amplified and made more durable, which would be required for real clinical effectiveness," he writes.

Another hurdle will be to define subgroups that best respond to tDCS. "[O]ne might wonder how much preservation of the left prefrontal cortex and its connections is required for the effect, whether this stimulation site is optimal for all patients, and whether the changes in brain morphology that often follow severe brain injury might complicate the relationship between electrode placement and current delivery to relevant tissues."

If a single session can identify treatment responders, "tDCS may provide a useful screening approach for other treatment studies, as well as a useful treatment in its own right," Dr. Whyte concludes.

The authors and Dr. Whyte have disclosed no relevant financial relationships.

Neurology. 2014;82:1112-1118, 1106-1107. Abstract Editorial


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.