TDCS modulates cortical excitability in patients with disorders of consciousness

Abstract

Transcranial direct current stimulation (tDCS) has been reported to be a promising technique for consciousness improvement for patients with disorders of consciousness (DOC). However, there has been no direct electrophysiological evidence to demonstrate the efficacy of tDCS on patients with DOC. Therefore, we aim to measure the cortical excitability changes induced by tDCS in patients with DOC, to find electrophysiological evidence supporting the therapeutic efficacy of tDCS on patients with DOC. In this study, we enrolled sixteen patients with DOC, including nine vegetative state (VS) and seven minimally conscious state (MCS) (six females and ten males). TMS-EEG was applied to assess cortical excitability changes after twenty minutes of anodal tDCS of the left dorsolateral prefrontal cortex. Global cerebral excitability were calculated to quantify cortical excitability in the temporal domain: four time intervals (0-100, 100-200, 200-300, 300-400 ms). Then local cerebral excitability in the significantly altered time windows were investigated (frontal, left/right hemispheres, central, and posterior). Compared to baseline and sham stimulation, we found that global cerebral excitability increased in early time windows (0-100 and 100-200 ms) for patients with MCS; for the patients with VS, global cerebral excitability increased in the 0-100 ms interval but decreased in the 300-400 ms interval. The local cerebral excitability was significantly different between MCS and VS. The results indicated that tDCS can effectively modulate the cortical excitability of patients with DOC; and the changes in excitability in temporal and spatial domains are different between patients with MCS and those with VS.

Keywords: Cortical excitability; Disorder of consciousness; TMS-EEG; tDCS.

Fig. 1

A schematic representation of the experimental procedure. Each experimental session began with a TMS-EEG block, 200 single pulse TMS delivered to L-DLPFC with 90%RMT intensity. Then, real or sham anodal tDCS was delivered to L-DLPFC with cathode over the right supraorbital area. Stimulation lasted 20 min, and a TMS-EEG block immediately followed.

Fig. 2

EEG response to TMS pulses by one MCS and one VS patient. (A) Average TEP pre-tDCS and significant activation spatial patterns at each peak. (B) Average TEP post-tDCS and significant activation spatial patterns at each peak. (C) GMFA traces for pre-tDCS (blue) and post-tDCS (red). Shadow areas show plus and minus one standard deviation. Black lines above the traces indicate significance with paired t-test, p < 0.05;

Fig. 3

Mean GMFA in different time windows. (A) GMFA of MCS (left column) and VS (right column) for real stimulation. (B) GMFA of MCS (left column) and VS (right column) for sham stimulation. * indicates p < 0.05 and ** indicates p < 0.01.

Fig. 4

Mean LMFA for real stimulation. (A) Brain was divided into five regions for LMFA calculation: frontal, left hemisphere, central, right hemisphere, and posterior. (B) Mean LMFA of MCS patients in time windows of 0-100 ms and 100-200 ms for the five regions. And mean LMFA of VS patients in time windows of 0-100 ms and 300-400 ms for the five regions. * indicates p < 0.05.