Table 1.
High-definition electrical stimulation.
| Reference | Sample size (n) | Stimulation type | Parameter location | Parameter intensity | Duration | Main outcome |
|---|---|---|---|---|---|---|
| Lang et al. (2019) | 60 (age: 18–45 years) | HD-tACS | FP1, P2, P3, PO7, P10 | 6 Hz, Fp1: −0.62 mA, P2: −0.99 mA, P3: −0.14 mA, P7: −0.24 mA, P10: 2 mA (peak to baseline) | 10 min | Consistent with our hypothesis, improved AM performance was observed in the TACS group, while TDCS had no effect. |
| Berger et al. (2018) | 24 (12 females, 12 males, age: 18–30 years) | HD-tACS | P3, P4 | 10 Hz/20 Hz, 1 mA | 20 min | After HD-tACS stimulation, the alpha activity in the parietal lobe increased significantly, and the concentration of HbOxy in right hemisphere motor cortex decreased significantly. |
| Wischnewski et al. (2018) | 11 (9 females, 2 males, age: 23.1 ± 3.4) | HD-tACS | C3, T7, F3, Cz, P3 | 20 Hz, 2 mA | 15 min | tACS can induce NMDAR-mediated plasticity in the motor cortex. |
| Alekseichuk et al. (2017) | 25 (13 females, 12 males, age: 23.5 ± 2.9 years) | HD-tACS | AF3, P3, AF4, P4 | 6 Hz, 1 mA (peak to baseline) | 18 min | A decrease in memory performance and an increase in reaction time was caused by frontoparietal intra-hemispheric desynchronization. |
| Alekseichuk et al. (2019b) | 25 (13 female, 12 males, age: 18–28 years) | HD-tACS | P4, T8, C2, CP1, Oz | 4 Hz, 3 mA | 20 min | Stimulation over the right posterior brain area augmented subsequent long-term recognition memory. |
| Khatoun et al. (2018) | 13 (4 females, 9 males, age: 24 ± 5) | HD-tACS | C3, C1, C5, CP3, FC3/C4, C2, C6, CP4, FC4/Pz, Oz, Pz, PO4, PO3 | 10 Hz, 5 mA | 12 min | High-amplitude focused HD-tACS can entrain physiological tremor. |
| Reinhart (2017) | 97 (45 females, 52 males) | HD-tACS | MFC, lPFC | 6 Hz, 1 mA | 20 min | Executive functions can be rapidly up- or downregulated by modulating theta phase coupling of distant frontal cortical areas |
| Zoefel et al. (2019) | 19 (8 females, 11 males, age: 21 ± 2 years) | HD-tACS | T7, T8 | 3.125 Hz, 1.2 mA | 19 min | tACS induces speech perception modulation, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). |
| Helfrich et al. (2014) | 14 (8 females, 6 males, age: 27.5 ± 6.7 years) | HD-tACS | C3, C4, O1, O2/P7, PO7, P8, PO8 | 40 Hz, 1 mA | 20 min | In-phase stimulation enhanced synchronization of inter-hemispheric functional connectivity, and anti-phase stimulation impaired functional coupling. |
| Schwab et al. (2019) | 24 (12 female, 12 males, age: 26 ± 4) | HD-tACS | P7, PO7, P8, PO8 | 9.5–10.5 Hz, 2 mA | 13 min | Global pre–post stimulation changes in EEG connectivity were larger after in-phase stimulation than after anti-phase or jittered-phase stimulation. |
| Popp et al. (2019) | 28 (14 females, 14 males, mean age: 24.4 years) | HD-tACS | C3, C4, CP3, CP4, P3, P4/T7, T8, TP7, TP8, P7, P8 | 1–7.5 Hz, 1 mA | 20 min | TACS and sham conditions did not differ regarding their reaction times in response to target stimuli or their event-related spectral perturbation (ERSP) at stimulation frequency. |
| Tomer et al. (2018) | 62 | HD-tACS | F3, F4, C3, C4, P3, P4, O1, O2 | Determined by a staircase procedure | 20 min | Alpha oscillations did not increase after HD-tACS relative to the sham condition. |
| Nguyen et al. (2018) | 32 (16 females, 16 males, mean age: 24 years) | HD-tACS | MFC, right lPFC | 6 Hz, 1 mA | 20 min | HD-tACS with participants’ eyes open improved learning ability relative to sham stimulation, whereas HD-tACS with participants’ eyes closed had no significant effect on behavior. |
| Deng et al. (2019) | 38 (28 females, 10 males, age: 18–24 years) | HD-tACS | P2, CP2, P4, Pz, PO4 | 10 Hz/6 Hz, 1.5 mA | 20 min | Parietal alpha brain stimulation affects top-down control of auditory spatial attention with causal, frequency, hemispherical and task-specific effects. |