Neurophysiological Correlates of a Single Session of Prefrontal tDCS in Patients with Prolonged Disorders of Consciousness: A Pilot Double-Blind Randomized Controlled Study

Abstract

Background. Transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (lDLPFC) was reported to promote the recovery of signs of consciousness in some patients in a minimally conscious state (MCS), but its electrophysiological effects on brain activity remain poorly understood. Objective. We aimed to assess behavioral (using the Coma Recovery Scale—Revised; CRS-R) and neurophysiological effects (using high density electroencephalography; hdEEG) of lDLPFC-tDCS in patients with prolonged disorders of consciousness (DOC). Methods. In a double-blind, sham-controlled, crossover design, one active and one sham tDCS (2 mA, 20 min) were delivered in a randomized order. Directly before and after tDCS, 10 min of hdEEG were recorded and the CRS-R was administered. Results. Thirteen patients with severe brain injury were enrolled in the study. We found higher relative power at the group level after the active tDCS session in the alpha band in central regions and in the theta band over the frontal and posterior regions (uncorrected results). Higher weighted symbolic mutual information (wSMI) connectivity was found between left and right parietal regions, and higher fronto-parietal weighted phase lag index (wPLI) connectivity was found, both in the alpha band (uncorrected results). At the group level, no significant treatment effect was observed. Three patients showed behavioral improvement after the active session and one patient improved after the sham. Conclusion. We provide preliminary indications that neurophysiological changes can be observed after a single session of tDCS in patients with prolonged DOC, although they are not necessarily paralleled with significant behavioral improvements.

A novel closed-loop EEG-tDCS approach to promote responsiveness of patients in minimally conscious state: A study protocol

“…Further trials confirmed clinical effects (as measured by behavioral improvements observed on the CRS-R), even if moderate, of tDCS applied over the DLPFC, especially for MCS patients [12][13][14][15][16][17]. However, the clinical effects seem inconsistent as several J o u r n a l P r e -p r o o f trials showed no relevant behavioural improvements using the same type of montage [18][19][20] or multichannel montages [21].…”

“…For instance, Luna et al found a modulation of alpha power that was different according to the region stimulated and was not correlated with changes in performance [22]. In another recent pilot study, Carrière and colleagues identified a tendency for higher power in the alpha and theta band at the group level after active tDCS and higher connectivity in the alpha band between left and right parietal regions, and in fronto-parietal regions [19]. In a study investigating tDCS with TMS-EEG [20], reduced slow-wave activity and response slope were found following tDCS; both these measures are proxies of cortical bistability and correlated with J o u r n a l P r e -p r o o f high-frequency suppression.…”

“…Regarding the electrophysiological effects of tDCS in DOC, several works report significant electroencephalography (EEG) changes following active stimulation (versus sham); both power and connectivity increases were described in the alpha and theta bands [19,22]. The relationship between power and connectivity changes in these bands and the behavioural improvements remains however intricate [23].…”

Therapeutic Use of Transcranial Direct Current Stimulation in the Rehabilitation of Prolonged Disorders of Consciousness

“…Wu et al ( 42 ) observed a trend toward higher EEG functional connectivity in frontal areas after 2 weeks of tDCS over the right and left DLPFC. More recently, Carrière et al ( 37 ) assessed weighted phase-lag index (wPLI), symbolic mutual Information (wSMI), and EEG power bands changes following anodal tDCS over the L-DLPFC in 13 MCS patients. They observed higher wSMI connectivity between left and right parietal regions, and higher fronto-parietal wPLI connectivity, although these changes only appeared when uncorrected for multiple comparisons.…”

Clinical diagnosis guidelines and neurorestorative treatment for chronic disorders of consciousness (2021 China version)

“…Transcranial direct current stimulation [28][29][30][31][32][33][34][35][36]. DLPFC or posterior parietal cortex at 10-20 min/time (1-2 mA for 10-20 days) was chosen.…”