Table 1.
Included articles on psychiatric applications
| Publication | Study design | Participants | Stimulation protocol | Study outcomes | Main Findings | ||||
|---|---|---|---|---|---|---|---|---|---|
| Author, Year | Sessions’ number | Session duration | Current amplitude (Peak-To-Peak) | Frequency | Electrode Location | ||||
| A. Schizophrenia | |||||||||
| Sreeraj et al. [125] | Case report | One patient with paranoid schizophrenia | Two sessions with 2 days apart | 20 min |
Session 1: 2 mA, session 2: 1 mA |
Session 1: 6 Hz, session 2: 40 Hz |
Left DLPFC (F3) and the left posterior parietal region (P3) | WM task | Improved performance in the WM task only with 6 Hz tACS |
| Sreeraj et al. [126] | Case report | One patient with paranoid schizophrenia | 5 sessions for 5 consecutive days | 20 min | 2 mA | 6 Hz | Left DLPFC (F3) and the left posterior parietal region (P3) | WM task |
- Improved working memory - Improvement in other cognitive domains - Persistence of improvement for 50 days |
| Kallel et al. [127] | Open case series | 3 clozapine-resistant patients with schizophrenia | 20 daily on weekdays for 4 consecutive weeks followed by 4-week follow-up | 20 min | 2 mA | 4.5 Hz | Both DLPFCs | SANS; PANSS; SUMD; HAMA; and side effects | Reduction in negative symptoms, anxiety and general psychopathology symptoms, and improvement in insight |
| Sreeraj et al. [128] | Open-label non-controlled clinical trial | 12 patients with schizophrenia and persistent delusions | Twice daily for 5 days, 9 patients continued for 5 more days, and another patient continued for 4 more days | 20 min | 2 mA | 10 Hz | Two electrodes on AFz and Cz | PSYRATS—Delusions, SAPS and SANS |
- Reduction in the delusion severity, positive and negative symptoms as well as tolerance of tACS - Maintained effect for one month |
| Hoy et al. [129] | Single-blind randomized controlled trial | 10 patients with schizophrenia | Three separate sessions at least 3 days apart | 20 min | 2 mA | 40 Hz-tACS, tDCS and sham stimulation | Left DLFPC | WM task | No significant tACS effects |
| Mellin et al. [4] | Double-blind randomized controlled trial | 22 patients with schizophrenia | Twice daily for 5 consecutive days | 20 min | 2 mA | 10 Hz, tDCS or sham | Left frontal and temporal lobes | Primary outcome: AHRS, secondary outcome: PANSS, BACS | No significant results |
| Ahn et al. [131] | Double-blind randomized controlled trial | 22 patients with schizophrenia | Twice daily for 5 consecutive days | 20 min | 2 mA | 10 Hz, tDCS or sham | Left frontal and temporal lobes | AHRS, hdEEG |
- 10 Hz-tACS showed modulated functional connectivity, and enhanced alpha oscillations and 40 Hz ASSR - This enhancement correlated with the reduction of auditory hallucinations |
| B. Depression | |||||||||
| Alexander et al. [150] | Double-blind, randomized pilot clinical trial | 32 MDD patients | 5 consecutive days | 40 min | 4 mA at Cz, 2 mA at F3 and F4 | 10 Hz-tACS, 40 Hz-tACS); or sham |
Bifrontal: Two electrodes over F3 and F4, and a third over the vertex |
Primary outcome: MADRS at 4-week follow-up, secondary: hdEEG, HDRS, BDI |
- No significant primary outcome - Two weeks after completion of the intervention, the 10 Hz-tACS group had more responders compared with 40 Hz-tACS and sham groups as well as a significant reduction in alpha power over the left frontal regions at day 5 |
| Riddle et al. [151] | Case report (extension of (Alexander et al., 2019)) | One female MDD patient | 12 weekly sessions | 40 min | 4 mA at Cz, 2 mA at F3 and F4 | 10 Hz-tACS | Bifrontal: Two electrodes over F3 and F4, and a third over the vertex |
Daily self-reported 10-point Likert scale, and monthly MADRS |
Remission (MADRS = 1 7) after twelve weeks |
| Wilkening et al. [152] | Case report | One female pregnant MDD patient | 9 weekly sessions | 20 min | 2 mA | 40 Hz-tACS with DC offset | Bifrontal: Two electrodes over F3 and F4 | HDRS, BDI, PANAS, and TMT | Improved scores after 9 stimulations, and after two-week follow-up. Remission after three months |
| C. OCD: | |||||||||
| Klimke et al. [3] | Cases series | 7 OCD treatment-resistant patients |
3 session per week. Treatment duration varied across patients Follow-up duration was 58 days and one year for 4 patients and the other three, respectively |
20 min | 650 µA | 40 Hz | Fp1-T3 and Fp2-T4 | YBOCS, CGI | The symptoms improved in all patients, and the improvement lasted throughout the follow-up duration |
| D. ADHD | |||||||||
| Dallmer-Zerbe et al. [185] | Randomized single-blind controlled study | 18 ADHD patients | One stimulation or Sham | 20 min | 1 mA | Timing and frequency personalized to coincide the stimulation peaks with P300 oscillation peaks | Multiple electrodes on the central, parietal and temporal lobes | EEG, visual oddball task | Increase in P300 amplitude in the stimulation group accompanied by a behavioural improvement defined by a decrease in omission errors |
| E. Dementia: | |||||||||
| Naro et al. [194] | Longitudinal case–control study | 35 AD and 25 MCI individuals and 27 age-matched health participants | Both sham and one of five verum stimulation sessions on a weekly basis | 10 min | 1 mA | A range between 40 and 120 Hz at steps of 20 Hz | Left M1, PMA, SMA, DLPFC, or DMPFC | EEG and different neuropsychological tests (see text) |
- Enhancement of gamma-band oscillations and a clinical improvement in MCI, but not AD patients - tACS predicted the progression from MCI to AD |