Table 1.
Effect of tDCS on fear memory and fear extinction in healthy and clinical groups.
| References | Study type | N/Groups | Gender M/F (Mean age ± SD) | Target area | Target/return electrode position | Polarity | Size | Online/offline stimulation | Intensity/duration | Type of CS/US | Reinforcement rate | Outcome measures | Outcome direction |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| FEAR MEMORY | |||||||||||||
| Asthana et al. (2013) | RCT, sham controlled, single blind | 49 healthy participants/anodal, cathodal and sham | 24/25 (22.58 ± 2.24) |
Left dlPFC | F3/left mastoid | Anodal/cathodal | 35 cm2 | Offline, after acquisition and break (10–20 min) | 1 mA/12 min | Colored blue and yellow squares/Scream | 75% | SCR | Diminution of fear memory |
| Mungee et al. (2014) | RCT, sham controlled, single blind | 50 healthy participants/active and sham tDCSgroups | 28/22 (N.R.) |
Right dlPFC/vmPFC | F4/contralateral supraorbital area | Anodal | 15 cm2 | Offline, on day 2 immediately after reminding | 1 mA/20 min | Blue and yellow squares/Electrical shock | 38% | SCR | - Enhancement of fear memory |
| Mungee et al. (2016) | RCT, sham controlled, single blind | 17 healthy participants/active and sham tDCS groups | 5/12 (N.R.) |
Right dlPFC/vmPFC | F4/contralateral supraorbital area | Cathodal | 15 cm2 | Offline, on day 2 immediately after reminding, | 1 mA/20 min | Blue and yellow squares/Electrical shock | 38% | SCR | - No effect on fear memory |
| FEAR EXTINCTION | |||||||||||||
| Abend et al. (2016) | RCT, sham controlled, double blind | 45 healthy participants/tDCS, tACS and sham groups | 24/21 (25.2 ± 5.7) |
mPFC | Between Fpz and Fp1/occipital bone (Oz) | Anodal | 35 cm2 | Online, during extinction | 1.5 mA/20 min | Two female faces/Scream | 80% | SCR, self-reported fear | - Anodal tDCS led to overgeneralization |
| van't Wout et al. (2016) | RCT, sham controlled, single blind | 44 healthy participants/active and sham tDCS groups | 23/21 (27.34 ± 8.18) |
Left vmPFC | AF3/contralateral mastoid | Anodal | 15 cm2 | Online, started before and continued during extinction | 2 mA/10 min | Red, blue and yellow lights/Electrical shock | 60% | SCR | - tDCS during the first extinction block enhanced late extinction of the second extinction block |
| Dittert et al. (2018) | RCT, sham controlled, double blind | 84 healthy participants/two active and two sham tDCS groups | 38/46 (24.25 ± 4.07) |
Right and left vmPFC | Electrodes positions: M20, M21, I20, I21, J13, J14 for the left and M9, M10, I9, I10, J6, J7 for the right electrode pad (slightly below F7 and F8) | Anodal | 16 cm2 | Online, started during the break between acquisition and extinction and lasted until the end of the extinction | 1.5 mA/20 min | Two female faces/Scream | 80% | SCR, self-report measures (valence, arousal and CS-US contingency STAI-X1, PANAS) | -Enhancement of early extinction - No differential effect of current flow direction on early extinction - left anodal tDCS reduced state anxiety |
| Ganho-Ávila et al. (2019) | RCT, sham controlled, single blind | 41 healthy participants/cathodal and sham tDCS groups | 0/41 (20.42 ± 4.99) |
Right dlPFC | F4/contralateral deltoid | Cathodal | 24.75cm2 | Offline, on day 2, after verbal recall of CS+ color | 1 mA/20 min | Blue and yellow squares/Scream | 75% | SCR, self-report measures (valence, arousal, contingency and expectancy), STAI-S, AAT. | - No short-term effect on fear extinction - Enhancement of fear memory retention - Enhancement of stimuli discrimination |
| Vicario et al. (2020b) | RCT, sham controlled, single blind | 23 healthy participants/anodal and sham tDCS groups | 10/13 (24.15 ± 4.92) |
Left vmPFC | AF3/contralateral mastoid | Anodal | 25 cm2 | Online, during extinction | 2 mA/20 min | Colored circles/Electrical shock | 71% | SCR | -Enhanced fear extinction and recall |
| Ney et al. (2021) | RCT, sham controlled, single blind | 30 healthy participants/anodal and sham tDCS groups | 10/20 (24.60 ± 7.30) |
Left vmPFC | AF3/contralateral mastoid | Anodal | 25 cm2 | Offline, after extinction | 2 mA/10 min | Colored circles/Electrical shock | 62.5% | SCR | - Anodal tDCS impaired fear extinction retention on day 2 |
| CLINICAL GROUPS | |||||||||||||
| van't Wout et al. (2017) | RCT, sham controlled Blinding mode not reported | 28 PTSD/two groups (stimulation during extinction learning vs after extinction) | 28/0 (56.25 ± 12.3) |
Left vmPFC | AF3/contralateral mastoid process | Anodal | 25 cm2 | Online and offline, during and after extinction | 2 mA/10 min (single-session) | Red, blue and yellow light./Electrical shock | 60% | SCR | - Enhanced early fear extinction recall when tDCS was applied after extinction |
| Todder et al. (2018) | RCT, within-subject sham controlled, double blind | 12 refractory OCD patients/one group | 7/5 (38.5 ± 12) |
mPFC | Fpz/right shoulder | Anodal/cathodal | 35 mm2 | Offline, after exposure and between presentation of obsession provoking stimuli | 2 mA/20 min (3 sessions for each polarity) | Individualized anxiety provoking stimuli | N/A | 7-point VAS, Y-BOCS, HAMA, MADRS | - Reduction of obsession-induced anxiety after cathodal stimulation |
| van't Wout-Frank et al. (2019) | RCT, sham controlled, single blind | 12 PTSD patients | 12/0 (40.5 ± 8.8) |
Left vmPFC | AF3/right posterior occipital (PO8) | Anodal | 25 cm2 | tDCS started simultaneously with VR, online | 2 mA/25 min (6 sessions) | N/A | N/A | SCR, self-reported PTSD symptoms | - Greater decrease in SCR in real tDCS group - RealtDCS group continued to improve during the 1-month follow-up. |
DlPFC, dorsolateral prefrontal cortex; Mpfc, medial prefrontal cortex; vmPFC, ventromedial prefrontal cortex; VR, virtual reality; OCD, Obsessive-Compulsive disorder; PTSD, Posttraumatic stress disorder; SCR, Skin conductance response; STAI-X1, State-trait anxiety inventory-state form; PANAS, Positive and Negative Affect Schedule; VAS, visual analog scale; AAT, approach avoidance task; MADRS, Montgomery-Åsberg Depression Rating Scale; Y-BOCS, Yale-Brown Obsessive-Compulsive Scale; HAMA, Hamilton Anxiety Rating Scale; N/A = not applicable.