TABLE 1.
Characteristics of included studies in this review.
| References | Study design | Participants | Intervention | Brain target | Duration | Outcome |
| Barra et al. (2022) | Double blind, randomized, cross-over | 12 DOC | Group 1: 6–10 Hz tPCS with a biphasic current of 2 mA peak to peak Group 2: maximum of 2 mA anodal tDCS Group 3: sham stimulation 5-day washout |
Bi-mastoid LDLPFC (F3) |
tDCS: 20 min for one session tPCS: 20 min for one session |
EEG CRS-R Side effect |
| Cavinato et al. (2019) | Double blind, randomized, cross-over | 24 DOC (12 MCS, 12 UWS) |
EG: 2 mA anodal tDCS CG: sham tDCS 10-day washout |
LDLPFC (F3) | 20 min per session, 1 session per day, 5 days per week for 2 consecutive weeks | EEG CRS-R WNSSP |
| Chen et al. (2021) | Randomized, parallel group | 52 DOC | EG: 2 mA anodal tDCS paired with 50 Hz and 200 μs MNES CG: conventional therapy only |
LDLPFC (F3) Right median nerve |
tDCS: 20 min per session, 1 session per day, 6 days per week for 4 consecutive weeks MNSE: 30 min per session, 2 sessions per day, 6 days per week for 4 consecutive weeks |
GCS GOS DRS BAEP USEP |
| Chi et al. (2018) | Randomized, parallel group | 38 DOC | EG: 2 mA anodal tDCS paired with conventional therapy CG: conventional therapy only |
LDLPFC (F3) | 20 min per session, 1 session per day, 6 days per week for 20 sessions | BAEP USEP EEG GCS PVS |
| Estraneo et al. (2017) | Double blind, randomized, cross-over | 13 DOC (7 VS, 6 MCS) |
EG: 2 mA anodal tDCS CG: sham tDCS 1-week washout |
LDLPFC (F3) | 20 min per session, 1 session per day for five sessions | CRS-R EEG |
| Guo et al. (2021) | Randomized, parallel group | 113 DOC | EG: 1.4 mA anodal tDCS paired with perceptual level arousal intervention CG: perceptual level arousal intervention only |
LDLPFC (F3) | 20 min per session, 1 session per day, 6 days per week for 4 consecutive weeks | CRS-R GCS DFS EEG Latency of evoked action potential |
| Huang et al. (2017) | Double blind, randomized, cross-over | 37 MCS | EG: 2 mA anodal tDCS CG: sham tDCS 5-day washout |
LDLPFC (F3) | 20 min per session, 1 session per day for five sessions | CRS-R |
| Li et al. (2021) | Randomized, parallel group | 102 DOC | Group 1: 2 mA anodal tDCS paired with conventional therapy Group 2: 60 Hz and 250 μs MNES paired with conventional therapy Group 3: tDCS and MNES paired with conventional therapy |
LDLPFC (F3) Right median nerve |
20 min per session, 1 session per day, 6 days per week for 8 consecutive weeks | Somatosensory evoked potential GCS |
| Martens et al. (2018) | Double blind, randomized, cross-over | 27 DOC | EG: 2 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy 8-week washout |
LDLPFC (F3) | 20 min per session, 1 session per day, 5 days per week for 4 consecutive weeks | Adverse events CRS-R |
| Martens et al. (2019) | Double blind, randomized, cross-over | 10 DOC (4 UWS, 6MCS) |
EG: 2 mA anodal tDCS CG: sham tDCS 24-h washout |
Primary motor cortex (C3-C4) | 20 min for one session | CRS-R |
| Martens et al. (2020) | Double blind, randomized, cross-over | 46 DOC (17 UWS, 23 MCS, 6 EMCS) |
EG: tDCS with 4 anodes and 4 cathodes, 1 mA per anode CG: sham tDCS 2–6-day washout |
Anodes placed on F3, F4, CP5 and CP6 | 20 min for one session | CRS-R EEG |
| Thibaut et al. (2014) | Double blind, randomized, cross-over | 25 VS/UWS 30 MCS |
EG: 2 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy 2-days washout |
LDLPFC (F3) | 20 min a single session | CRS-R |
| Thibaut et al. (2017) | Double blind, randomized, cross-over | 16 MCS | EG: 2 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy 1-week washout |
LDLPFC (F3) | 20 min per session, 1 session per day for 5 consecutive days; | CRS-R |
| Thibaut et al. (2019a) | Double blind, randomized, cross-over | 14 DOC | EG: 1 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy 2-days washout |
LDLPFC (F3) RDLPFC (F4) |
20 min a single session | MAS CRS-R EEG |
| Wu et al. (2019) | Randomized, parallel group | 15 DOC | Group 1: 2 mA anodal tDCS anode placed over the left DLPFC paired with conventional therapy Group 2: 2 mA anodal tDCS anode placed over the right DLPFC paired with conventional therapy Group 3: sham tDCS paired with conventional therapy |
LDLPFC (F3) RDLPFC (F4) |
20 min per session, 1 session per day, 10 working days (from Monday to Friday in two consecutive weeks). | CRS-R GOS-E EEG |
| Zhang et al. (2017) | Double blind, randomized, parallel | 26 DOC (11VS, 15MCS) |
EG: 2 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy |
LDLPFC (F3) | 20 min per session, 2 session per day, 10 consecutive working days (from Monday to Friday). | CRS-R ERP |
| Zhang et al. (2020) | Double blind, randomized, parallel group | 18 MCS | EG: 2 mA anodal tDCS paired with conventional therapy CG: sham tDCS paired with conventional therapy |
LDLPFC (F3) | 20 min per session, 2 sessions per day for 10 consecutive working days | CRS-R ERP |
CG, control group; DIT, diffusion tensor imaging; BAEP, brain stem auditory evoked potential; DRS, disability rating scale; EEG, electroencephalogram; EG, experimental group; EMCS, emerged from minimally conscious state; EMG, electromyography; ERP, event-related potentials; FOUR, full outline of unresponsiveness scale; GCS, Glasgow coma scale; GOS, Glasgow outcome scale; L/RDLPFC, left/right dorsolateral prefrontal cortex; MBI, modified Barthel index; MCS, minimally conscious state; PVS, persistent vegetative state; tDCS, transcranial direct current stimulation; tPCS, transcranial pulsed-current stimulation; USEP, upper limb somatosensory evoked potential; UWS, unresponsive wakefulness syndrome; WNSSP, western neurosensory stimulation profile.