Transcranial direct current stimulation in disorders of consciousness

Abstract

Transcranial direct current stimulation (tDCS), a noninvasive cortical stimulation modulating cortical excitability, has been previously reported to transiently improve working memory and attention by stimulating the left dorsolateral prefrontal cortex (DLPF) in patients with stroke as well as Parkinson's and Alzheimer's disease. As regards disorders of consciousness (DOC), we have recently shown that a single session of tDCS over the left DLPFC can improve sign of consciousness in about 43 % of patients in minimally conscious state (MCS). The transient clinical improvement observed in patients in MCS following tDCS seem to require residual grey matter and metabolic activity in the stimulated area and in structures known to be involved in awareness and arousal, such as the precuneus and the thalamus. These findings suggest that tDCS might be a feasible treatment to promote recovery of new signs of consciousness in patients with DOC. Nevertheless, it also suggests that some patients may be more suited to benefit from tDCS than others. Apart from clinical treatment, tDCS combined with transcranial magnetic stimulation has been shown to induce different responses in terms of connectivity and excitability in MCS as compared with unresponsive patients. Although tDCS on patients with DOC has not been yet fully investigated, the so far reported studies have revealed promising results as regards improvement of signs of consciousness. We here provide an overview of the tDCS studies on patients with DOC.