Table 1.
Authors | Participants and Design | Task and Dependent Variables | Electrode Montage and Device | Stimulation Parameters | Outcome/Risk Bias |
---|---|---|---|---|---|
Attention | |||||
Alpha | |||||
[30] |
N = 36 (mean age: 21.56 years, range 18–29 years) Crossover within-subject design (tACS vs. sham) |
Endogenous and exogenous spatial attention task Reaction time bias score |
Left parietal cortex (P3) + centered above target electrode Device: high-definition tES (NeuroConn, Ilmenau, Germany) |
Frequency: 10 Hz/sham Intensity: 1 mA peak-to-peak Duration: 35–40 min Electrode size: target electrode (round-shaped, diameter: 2.1 cm), return electrode (round-shaped, outer diameter: 11 cm, inner diameter: 9 cm) Timing: online |
↗ (for endogenous task only) Low risk |
[31] |
Exp. 1 N = 20 (mean age: 26.6 ± 4.1 years) Exp. 2 N = 18 (mean age: 22.11 ± 2.4 years) All Exp. Crossover within-subject design (tACS vs. sham) |
Selective auditory attention task Number of /ga/-syllables in spatial (left or right direction) or non-spatial trials (female/male speakers) |
Parietal cortex (P2) + (CP2/P4/Pz/PO4) Soterix M × N 9 high definition-tES Stimulator (Soterix Medical, New York, NY) |
Frequency: Exp. 1 10 Hz/sham; Exp. 2 6 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min incl. 30 s ramp-in/-out Electrode Size: not provided Timing: online |
↘ (with alpha-tACS) − (with theta-tACS) Low risk |
[32] |
Exp. 1 N = 24 (mean age: 21) Exp. 2 N = 12 (mean age: 21.2 ± 0.2 years) All Exp. Crossover within-subject design (tACS vs. sham) |
Temporal order judgement task Forced-choice verbal report of stimuli order |
Exp. 1 Left somatosensory cortex (C3) or left posterior parietal cortex (P3) + ipsilateral lower cheek Exp. 2 Right posterior parietal cortex (P4) + ipsilateral lower cheek Device: Eldith (NeuroConn GmbH, Ilmenau, Germany) |
Frequency: 10 Hz/sham Intensity: 1 mA peak-to-peak Duration: 270 s Electrode size: both 5 × 5 cm Timing: online |
↗ Low risk |
Alpha and Beta | |||||
[33] |
Exp. 1 N = 18 (mean age: 20.66 ± 2.53 years) Crossover within-subject design (10 Hz versus 20 Hz versus sham) Exp. 2 N = 15 (mean age: 20.26 ± 2.35 years) Crossover within-subject design (sham vs. 10 Hz in-phase vs. 10 Hz anti-phase vs. 20 Hz in-phase vs. 20 Hz anti-phase) |
Attentional blink task Detection of second target stimuli |
Exp. 1 Right posterior parietal cortex (P4) + right deltoid Exp. 2 Right posterior parietal cortex (P4) and left frontal cortex (F3) + right deltoid Device: Exp. 1 BrainStim (EMS Medical, Bologna, Italy); Exp. 2 StarStim 8 (Neuroelectrics, Boston, Massachusetts) |
Frequency: Exp. 1 10 Hz/20 Hz/sham; Exp. 2 10 Hz in-phase/10 Hz anti-phase/20 Hz in-phase/20 Hz anti-phase/sham Intensity: 0.35 mA Duration: Exp. 1 35 min; Exp. 2 50 min Electrode size: Exp. 1 both 7 × 5 cm; Exp. 2 both round-shaped electrodes (25 cm2) Timing: online |
↗ (with anti-phase beta-tACS) − (with alpha-tACS or in-phase beta-tACS) Low risk |
Alpha and Gamma | |||||
[34] |
Exp. 1 N = 48 (mean age: 22.7 ± 2.9 years) Exp. 2 N = 37 (mean age: 22.7 ± 3.5 years) Exp. 3 N = 41 (mean age: 23.2 ± 2.7 years) Exp. 4 N = 43 (mean age: 23.1 ± 3.1 years) Crossover within-subject design (tACS vs. sham vs. control (50 Hz) tACS) |
Visual or auditory sustained attention tasks Correct responses, reaction times |
Occipital cortex (Oz) + vertex (Cz) Device: Starstim (Neuroelectrics, Barcelona) |
Frequency: 10 Hz/50 Hz/sham Intensity: 2 mA peak-to-peak Duration: 11 min Electrode size: both 25 cm2 (round-shaped) Timing: online |
↗ (with alpha-tACS) − (with gamma-tACS) Low risk |
[35] |
N = 23 (age range: 18–27 years) Crossover within-subject design (alpha tACS vs. gamma tACS vs. sham) |
Selective spatial attention task (endogenous or exogenous) Reaction times |
Inferior parietal lobe (P6) + vertex (Cz) Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/40 Hz/sham Intensity: 2 mA peak-to-peak Duration: Endogenous blocks: ~33 min Exogenous blocks: ~21 min Electrode size: target electrode 5 × 5 cm, return electrode 5 × 7 cm Timing: online |
↗ (with alpha-tACS) − (with gamma-tACS) Low risk |
[36] |
N = 20 (age range: 19–31 years) Crossover within-subject design (tACS vs. control vs. sham) |
Dichotic Listening task Correct responses |
Fronto-central and temporo-parietal cortex (FC5) + TP7 Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/47.1 Hz/sham Intensity: 1 mA peak-to-peak Duration: 25 min Electrode Size: both 7 cm2 (round-shaped, 3 cm in diameter) Timing: online |
alpha-tACS: ↗ (for left-attend condition) ↘ (for right-attend condition) gamma-tACS: ↘ (for left-attend condition) ↗ (for right-attend condition) Low risk |
[37] |
N = 26 (mean age: 28.5 ± 7.9 years) Crossover within-subject design (tACS vs. sham) |
Dichotic Listening task Correct responses |
Multifocal approach: (FT9 + FT10/F3 + F4/CP5 + CP6/P5 + P6) Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 40 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode Size: all electrodes round-shaped, 12 mm in diameter Timing: online |
↗ (for left ear-perception only) Low risk |
Gamma | |||||
[38] |
N = 20 (mean age: 25.8 ± 6.2) Crossover within-subject design (40 Hz vs. 60 Hz vs. 80 Hz vs. sham) |
Visual spatial attention task Correct responses |
Occipital area (Oz) + vertex (Cz) Device: DC-Stimulator Plus (NeuroConn, Ilmenau, Germany) |
Frequency: 40 Hz/60 Hz/80 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: Exp. 1: 45 ± 10 min, Exp. 2: 15 ± 5 min Electrode size: target electrode 4 × 4 cm, return electrode 7 × 4 cm Timing: online |
↗ (with 60 Hz gamma-tACS) − (with other tACS) Low risk |
Intelligence | |||||
Theta | |||||
[39] |
N = 20 (mean age: 24.9 ± 3.3 years) Crossover within-subject design (tACS vs. sham) |
Raven’s progressive matrices Correct responses |
left temporal cortex (T7) + C3 Device: DC-Stimulator Plus (NeuroConn, Ilmenau, Germany) |
Frequency: 5 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 15 min Electrode size: both 5 × 7 cm Timing: offline |
↗ (for difficult items only) Low risk |
Alpha | |||||
[40] |
N = 20 (mean age: 20.18 ± 0.40) Crossover within-subject design (tACS vs. sham) |
Raven’s progressive matrices Correct responses |
Frontal cortex (F3) + F4 Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 1 Hz above IAF/sham Intensity: Modus = 1.75 mA peak-to-peak (Range = 1 mA to 2 mA) Duration: 15 min Electrode Size: both 7 × 5 cm Timing: offline |
− Low risk |
Alpha and Gamma | |||||
[41] |
N = 22 (mean age: 23.00 ± 2.85 years) Crossover within-subject design (alpha tACS vs. gamma tACS vs. sham) |
Verbal intelligence task Correct responses |
Frontal cortex (F3) + F4 Device: Eldith (NeuroConn GmbH, Ilmenau, Germany) |
Frequency: 10 Hz/40 Hz/sham Intensity: 1 mA peak-to-peak Duration: 30 min incl. 100 cycles ramp-in/-out Electrode size: both 5 × 7 cm Timing: online |
− Low risk |
Gamma and Theta | |||||
[42] |
Exp. 1 N = 24 (mean age: 23.8 ± 3.14 years) Exp. 2 N = 34 (mean age: 24.3 ± 2.76 years) Crossover within-subject design (tACS vs. sham vs. control) |
Modified version of Raven’s progressive matrices Correct responses, response times |
Frontal cortex (left MFG) + vertex (Cz) Device: Eldith DC-Stimulator, NeuroConn, Germany |
Frequency: Exp. 1 40 Hz/ 5 Hz/sham; Exp. 2 40 Hz/sham Intensity: 0.75 mA peak-to-peak Duration: ~30 min Electrode Size: both 5 × 5 cm Timing: online |
↗ (with gamma-tACS, benefit for low performer only) − (with other tACS) Low risk |
Multiple Frequencies | |||||
[43] |
N = 20 (mean age: 20.2 ± 12.3 years) Crossover within-subject design (tACS vs. sham vs. control) |
Raven’s progressive matrices Correct responses, response times |
Frontal cortex (left MFG) + vertex (Cz) Device: Eldith DC-Stimulator, NeuroConn, Germany |
Frequency: 5 Hz/10 Hz/20 Hz/40 Hz/sham Intensity: 0.75 mA peak-to-peak Duration: through task (~48 min), per condition Electrode Size: both 5 × 7 cm Timing: online |
↗ (with gamma-tACS) − (with other tACS) Low risk |
Visual Perception | |||||
Alpha | |||||
[44] |
N = 96, divided into 4 groups with each N = 24 6 Hz (mean age: 21 ± 2.4 years) 10 Hz (mean age: 21 ± 3.2 years) 25 Hz (mean age: 22 ± 2.1 years) sham (mean age: 22 ± 2.3 years) Between-subject design |
Visual detection and discrimination task Correct responses |
Parieto-occipital cortex (PO7/PO8) + vertex (Cz) Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/10 Hz/25 Hz/sham Intensity: 1 mA peak-to-peak Duration: 5 min Electrode size: target electrode 16 cm2, return electrode 35 cm2 Timing: online |
↘ (with theta- or alpha-tACS) Low risk |
[45] |
N = 15 (mean age: 24.3 ± 0.7 years) Crossover within-subject design |
Visual rotation detection task Correct responses |
Visual cortex stimulation montage (Oz) + Cz Retinal stimulation montage (Fpz) + Cz Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: IAF/IAF+4 Hz/IAF–4 Hz Intensity: Oz–Cz: 0.96 ± 0.3; Fpz–Cz: 2.31 ± 1.1 mA peak-to-peak Duration: 27 min (~5.4 s per frequency-montage combination) Electrode size: both 5 × 5 cm Timing: online |
↘ Low risk |
Gamma | |||||
[46] |
N = 60 (mean age: 32.22 ± 7.96 years) 40 Hz (N = 12) 40 Hz (N = 16) 5 Hz (N = 16) sham (N = 16) Between-subject design |
Face perception task, object perception task, Correct responses, reaction times |
Occipital cortex (PO8) + frontal cortex (FP1) Device: Neuroelectrics, Barcelona, Spain |
Frequency: 40 Hz/5 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode size: both 25 cm2 Timing: offline |
↗ (with gamma-tACS) − (with theta-tACS) Low risk |
[47] |
N = 45 (mean age: 24.9 ± 4.1) Exp. 1 N = 17 Exp. 2 N = 13 Exp. 3 N = 15 All Exp. Crossover within-subject design |
Stroboscopic alternative motion task Motion dominance index (% duration of perceived motion direction) |
Exp. 1 and Exp. 2: parieto-occipital cortex (P7-PO7) + (P8-PO8) Exp. 3: Central (C3/C4) + occipital areas (O1/O2) Device: NeuroConn, Ilmenau, Germany |
Frequency: Exp. 1 anti-phase 40 Hz tACS/sham; Exp. 2 antiphase 6 Hz/sham; Exp. 3 in-phase 6 Hz/40 Hz/sham Intensity: 0.5–1.5 mA peak-to-peak Duration: 15 min Electrode size: Exp. 1 and Exp. 2: both 5 × 7 cm; Exp. 3: both 3.9 × 3.9 cm Timing: online |
↘ (with anti-phase gamma-tACS) − (with other tACS) Low risk |
Auditory Perception | |||||
Delta/Theta | |||||
[48] |
N = 17 (mean age: 33 ± 8 years) Crossover within-subject design |
Word detection task Correct responses |
Left temporal cortex (T7) + C3 Device: DC-Stimulator MR (NeuroConn, Ilmenau, Germany) |
Frequency: 3.125 Hz/sham Intensity: 1.7 mA peak-to-peak Duration: ~30 min Electrode size: target electrode 3 × 3 cm, return electrode 5 × 7 cm Timing: online |
− High risk (small sample sizes) |
[49] |
Exp. 1 N = 27 (mean age: 31 ± 7 years) Exp. 2 N = 19 (mean age: 21 ± 2 years) Crossover within-subject design |
Speech perception task Correct responses |
Exp. 1 Unilateral montage: left temporal cortex (T7) + C3 Exp. 2 Bilateral montage: temporal cortex (T7/T8) + 2 large ring electrodes (around target electrode) Device: NeuroConn DC Stimulator MR (NeuroCare, Ilmenau, Germany) |
Frequency: 3.125 Hz/sham Intensity: Exp. 1 1.2 mA peak-to-peak; Exp. 2 1.7 mA peak-to-peak Duration: ~30 min Electrode Size: both 5 × 7 cm Timing: online |
Bilateral stimulation: ↗ (when stimulation and speech were aligned) ↘ (when stimulation and speech were not aligned) − (unilateral stimulation) Low risk for Exp. 1 High risk for Exp. 2 (small sample size) |
Theta | |||||
[50] |
N = 20 (age range: 18–38 years) Crossover within-subject design |
Stream perception task Correct responses |
Temporal cortex (T7/T8) + L/R side of midline (Cz) Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 4 Hz/sham Intensity: 0.8 ± 0.1 mA peak-to-peak Duration: 40 min Electrode Size: both target electrodes 5 × 5, both return electrodes 5 × 7 cm Timing: online |
↗ (when streams were synchronous with entrained oscillatory activity) Low risk |
[51] |
N = 22 (age range: 18–28 years) Crossover within-subject design |
Speech perception task Correct responses |
Temporal cortex (T7/T8) + Cz Device: DC-Stimulator MR (NeuroConn, Ilmenau, Germany) |
Frequency: 4 Hz/sham Intensity: Exp. 1: 0.9 ± 0.1 mA peak-to-peak, Exp. 2: 1 ± 0.1 mA peak-to-peak Duration: 36 min Electrode size: both target electrodes 5 × 5 cm, return electrode 10 × 7 cm Timing: online |
↗ Low risk |
Alpha and Beta | |||||
[52] |
N = 26 (mean age: 21.4 ± 4.7 years) Crossover within-subject design |
Phonological decision task Correct responses, reaction times |
Fronto-temporal cortex (Crossing point of T3-Fz × F7-Cz) + (T4-Fz × F8-Cz) Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/16.18 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode Size: both 9 cm2 (round-shaped) Timing: offline |
With alpha-tACS: ↗ (reaction time) ↘ (error rates) − (with other tACS) Low risk |
Gamma and Theta | |||||
[53] |
Exp. 1 N = 21 (mean age: 24.3 ± 2.0 years) Exp. 2 (control) N = 17 (mean age: 27.5 ± 3.3 years) All Exp. Crossover within-subject design |
Phonetic categorization task Correct responses, perceptual learning |
Exp. 1 only temporal areas (T7) + T8 Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: Exp. 1 40 Hz/6 Hz; Exp. 2 No stimulation Intensity: 1 mA peak-to-peak Duration: 18 min in total, in 6 min blocks Electrode Size: both 5 × 7 cm Timing: online |
↗ (with gamma-tACS in older adults) ↘ (with gamma-tACS in younger adults) − (with theta-tACS) Low risk |
[54] |
N = 25 (mean age: 24.1 ± 2.24 years) N = 20 (mean age: 69.8 ± 4.4 years) Between-subject/Crossover design |
Phonetic categorization task Correct responses, perceptual learning |
Temporal cortex (T7) + T8 Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 40 Hz/6 Hz Intensity: 1 mA peak-to-peak Duration: 10 min Electrode Size: both 5 × 7 cm Timing: online |
↘ (with gamma-tACS) ↗ (with theta-tACS) Low risk |
Executive functions | |||||
Theta | |||||
[55] |
N = 23 (mean age: 22.91 years, range 18–30) Crossover within-subject design |
Go/NoGo task Correct responses, reaction times |
Fronto-temporal area (T4-Fz × F8-Cz) + supraorbital Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode Size: both 5 × 5 cm Timing: online/offline |
− Low risk |
[56] |
N = 90 (N = 30 for each experiment) Exp. 1 mean age: 26 years Exp. 2 mean age: 27 years Exp. 3 mean age: 26 years Crossover within-subject design |
Time estimation task Correct responses |
Exp. 1/3 medial frontal and lateral prefrontal cortex (right: MFC/IPFC) + 4 surrounding return electrodes Exp. 2 similar to Exp. 1, but left hemisphere Device: M x N 9 high-definition Stimulator (Model 9002A, Soterix Medical, New York, NY) |
Frequency: 6 Hz in-phase/anti-phase/35 Hz/sham Intensity: 1 mA peak-to-peak Duration: Exp. 1/2: 20 min; Exp. 3: 20 min Electrode size: high definition-tACS Timing: online |
↗ (tACS on right hemisphere) − (tACS on left hemisphere or gamma-tACS) Low risk |
Theta and Alpha | |||||
[57] |
N = 31 (age range: 19-31 years) Crossover within-subject design |
Simon task Correct responses, response times |
left frontal cortex (between FCz and Cz) + both cheeks Device: DC-Stimulator MR (NeuroConn, Ilmenau, Germany) |
Frequency: ITF, IAF Intensity: 2 mA peak-to-peak Duration: ~20 min Electrode size: target electrode 9 cm2, both return electrodes 35 cm2 Timing: online |
↗ (with theta-tACS) − (with alpha-tACS) Low risk |
Alpha | |||||
[58] |
N = 20 (mean age: 26 ± 3 years) tACS (N = 10) sham (N = 10) Between-subject design |
Mental rotation task Correct responses, reaction times |
Occipital cortex (Oz) + vertex (Cz) Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: 10.5 ± 0.9 Hz/sham Intensity: 0.7 ± 0.3 mA peak-to-peak Duration: 20 min Electrode size: target electrode 4 × 4 cm, return electrode 5 × 7 cm Timing: online |
↗ (accuracy) Low risk |
Alpha and Beta | |||||
[59] |
N = 19 (mean age: 24 ± 4 years) Crossover within-subject design |
Temporal bisection task Choice (long or short) Reaction times |
SMA (FC1) + FC2 Device: NeuroConn MagStim (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/20 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode size: both 5 × 5 cm Timing: online |
↗ Low risk |
Multiple Frequencies | |||||
[60] |
N = 36 (mean age: 24.4 ± 3.5 years) Crossover within-subject design |
Flanker task Speed-accuracy-trade off and reaction times |
Medial-frontal Cortex (FCz) + Pz Device: Neuroelectrics, Barcelona, Spain |
Frequency: 2 Hz/6 Hz/11 Hz/21 Hz/60 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode size: both 25 cm2 Timing: online |
↗ (with theta-tACS) − (with other tACS) Low risk |
Decision-making | |||||
Multiple Frequencies | |||||
[61] |
N = 34 in total left frontal montage: N = 17 (mean age: 20.52 ± 2.52 years) right frontal montage: N = 17 (mean age: 21.17 ± 2.78 years) Between-subject design |
Decision making task Gains and losses and response times |
Left frontal cortex (F3) + ipsilateral shoulder Right frontal cortex (F4) + ipsilateral shoulder Device: BrainStim, EMS Medical, Bologna, Italy |
Frequency: 5Hz/10 Hz/20 Hz/40 HZ/sham Intensity: 1 mA peak-to-peak Duration: 40 min Electrode Size: both 5 × 7 cm Timing: online |
↘ (with beta-tACS to left hemisphere = riskier decisions) ↗ (with tACS to the right hemisphere) Low risk |
Procedural Memory (motor learning) | |||||
Theta | |||||
[62] |
N = 26 (mean age: 21.38 ± 1.52 years) Crossover within-subject design |
Implicit motor learning task Correct responses, reaction times |
Frontal area (FPz) + Pz Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode Size: both 5 × 5 cm Timing: online |
− Low risk |
Alpha | |||||
[63] |
N = 20 (mean age: 23.8 ± 3.90 years) N = 15 (mean age: 61.66 ± 3.71 years) Between-subject design (older vs. younger participants)/Crossover within-subject design |
Implicit motor learning task Correct responses, reaction times |
Central area (C3) + supraorbital region Device: Eldith DC Stimulator, NeuroConn ((NeuroCare, Ilmenau, Germany) |
Frequency: IAF/IAF + 2 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 10 min Electrode Size: target electrode 5 × 7 cm, return electrode 10 × 10 cm Timing: offline |
− (accuracy) Reaction times: ↗ (in older adults with IAF and IAF + 2 Hz) ↗ (in younger adults with IAF + 2 Hz only) Low risk |
Alpha and Beta | |||||
[64] |
N = 38 (mean age: 23 ± 3 years) Crossover within-subject design |
Movement selection task Duration between stimulus onset and verbal responses |
Central area (C3 or C4) + Pz Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/20 Hz/sham Intensity: 1.1 ± 0.3 mA peak-to-peak (range: 0.4–1.9 mA) Duration: ~30 min Electrode Size: both 5 × 5 cm Timing: online |
↗ (with alpha-tACS ipsilateral to requested hand) − (with beta-tACS) Low risk |
Beta and Gamma | |||||
[65] |
N = 20 (mean age: 24.9 years) Crossover within-subject design |
Cued reaction time task Reaction times |
Central area (left M1) + supraorbital region Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany); BiStim (MagStim) |
Frequency: IBF (or fixed 20.1 Hz)/75 Hz/sham Intensity: 0.69 ± 0.11 mA peak-to-peak; 1.3 ± 0.36 mA peak-to-peak Duration: 20 min Electrode Size: both 5 × 7 cm Timing: online |
↗ (with gamma-tACS) − (with beta-tACS) Low risk |
Gamma | |||||
[66] |
N = 17 (mean age: 24.5 ± 3.5 years) Crossover within-subject design |
Implicit motor learning task Reaction times |
Central area (left M1) + right supraorbital region Device: NeuroConn DC Stimulator (E.M.S., Bologna, Italy) |
Frequency: 1 Hz/40 Hz/sham Intensity: 2 mA peak-to-peak Duration: 5.08 ± 1.13 min Electrode Size: both 5 × 5 cm Timing: online |
↘ (with gamma tACS) − (with other tACS) Low risk |
Multiple Frequencies | |||||
[67] |
N = 55 (mean age: 32.7 ± 6.8 years) Crossover within-subject design |
Implicit motor learning task Correct responses, Reaction times |
Central area (C3) + supraorbital Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz/20 Hz/70 Hz/sham Intensity: 1 mA peak-to-peak Duration: 10 min Electrode Size: both 5 × 7 cm Timing: offline |
↗ (with gamma-tACS) − (with other tACS) Low risk |
Working memory | |||||
Theta | |||||
[68] |
N = 25 (mean age: 23.5 ± 2.9 years) Crossover within-subject design |
N-back task Correct responses, reaction times |
Frontal/parietal cortex Sync: AF3/P3 in-phase + AF4/P4 in-phase Desync: AF3/AF4 in-phase + P3/P4 in-phase Device: Starstim (Neuroelectrics, Barcelona) |
Frequency: 6 Hz/sham Intensity: 2 mA peak-to-peak Duration: 17–19 min Electrode Size: 3.14 cm2 (round-shaped) Timing: online |
↘ (with anti-phase tACS) − (with in-phase tACS) Low risk |
[69] |
Exp. 1 N = 18 (mean age: 29.8 ± 8.3 years) Exp. 2 N = 14 (mean age: 21.9 ± 5.9 years) Crossover within-subject design |
Delayed match-to-sample task Working memory capacity |
Parietal cortex (P4) + (Cz/Oz/T8) Device: Starstim (Neuroelectrics, Barcelona) |
Frequency: 4 Hz/7 Hz/sham Intensity: Exp. 1 1 mA peak-to-peak; Exp. 2 2 mA peak-to-peak Duration: at least 6 min per condition Electrode Size: target electrode 19.6 cm², each return electrode 4.9 cm² Timing: online |
↗ (with low theta-tACS, for items presented contralateral to stimulation site only) − (with high theta-tACS) Low risk for Exp. 1 High risk for Exp. 2 (small sample size) |
[70] |
N = 36 (mean age: 20 years ± 4.25 months) Between-subject design |
Corsi block-tapping task, Digit-span task, N-back task Working memory capacity, correct responses (n-back only) |
Left parietal cortex (P3) + supraorbital region Frontal cortex (F3) + supraorbital region Right parietal cortex (P4) + supraorbital region Device: NeuroConn DC Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: ITF/sham Intensity: 1–2.25 mA peak-to-peak Duration: 15 min Electrode Size: both 5 × 7 cm Timing: offline |
↗ Low risk (but imbalanced gender distribution: 27 females) |
[71] |
N = 48 (mean age: 23 years) Crossover within-subject design |
Visuo-spatial working memory task Working memory capacity |
Parietal cortex (P3/P4) + left cheek Exp. 1 in-phase between P3 and P4 Exp. 2 anti-phase between P3 and P4 Device: NeuroConn DC Stimulator MC (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/sham Intensity: 1.6 mA peak-to-peak Duration: 20–24 min Electrode Size: target electrode 4 × 4 cm, return electrode 5 × 7 cm Timing: online |
↗ (with in-phase for low performer) − (with anti-phase or in-phase for high performer) Low risk |
[72] |
N = 46 (age range: 22–30 years) Exp. 1: N = 10 Exp. 2: N = 18 Exp. 3 (control): N = 18 Crossover within-subject design |
Letter discrimination task Reaction times |
Exp. 1: no stimulation Exp. 2/3: Frontal/parietal cortex (F3/P3) + Vertex (Cz) Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: Exp. 1: no stimulation; Exp. 2: 6 Hz in-phase or anti-phase/sham; Exp. 3: 35 Hz in-phase or anti-phase/sham Intensity: Exp. 2/3 1 mA peak-to-peak Duration: Exp. 2/3 14 ± 1.5 min Electrode size: Exp. 2/3 all 5 × 5 cm Timing: Exp. 2/3 online |
↗ (with in-phase theta-tACS) − (with anti-phase theta- or gamma-tACS) Low risk |
[73] |
Exp. 1 N = 10 (mean age: 28.6 ± 5.0 years) Exp. 2 N = 21 (mean age: 27.38 ± 4.56 years) Crossover within-subject design |
Working memory tasks Exp. 1 2-back/1-back vs. choice reaction task Exp. 2 2-back vs. choice reaction task + MRT Correct responses, reaction times |
Exp. 1 and Exp. 2 frontal/parietal areas (F4/P4) + T8 All Exp. either in-phase or anti-phase between F4 and P4 Device: NeuroConn DC Stimulator MR (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/sham Intensity: 1 mA peak-to-peak Duration: Exp. 1: 26.5 min; Exp. 2: 20 min in short runs of 20 s or 30 s Electrode Size: all 5 cm diameter (‘donut’-shaped) Timing: online |
↗ (for choice reaction task with in-phase tACS) − (accuracy) High risk in Exp. 1 (small sample size) Low risk in Exp. 2 |
[74] |
N = 2 × 16 (mean age: 28.3 years (±7.6)/22.8 years (±5.2) Between-subject design (experimental vs. control montage)/Crossover within-subject design |
Visuo-spatial working memory task Correct responses, K-Value (Load x (Hits – False)) |
Target stimulation: Parietal cortex (P4) + supraorbital region Active control: Parietal cortex (P4) + Vertex (Cz) Device: Magstim DC-Stimulator Plus |
Frequency: 4 Hz/7 Hz/control (5.5 Hz) Intensity: 1.24 ± 0.3 mA peak-to-peak Duration: ~12 min Electrode Size: both 5 × 5 cm Timing: online |
for arrays pointing to the left: ↗ (with 4 Hz-tACS) ↘ (with 7 Hz-tACS) − (for arrays pointing to the right) Low risk |
Alpha | |||||
[75] |
N = 22 (mean age: 24.1 years) Between-subject design |
Spatial updating paradigm Updating bias |
Left parieto-occipital cortex (P3-O1) + vertex (Cz) Right parieto-occipital cortex (P4-O2) + vertex (Cz) Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: 10 Hz Intensity: 1 mA peak-to-peak Duration: 25 min Electrode size: target electrode 4 × 3 cm, return electrode 9 × 5 cm Timing: online |
↗ Low risk |
Gamma | |||||
[76] |
N = 18 (mean age: 29.3 ± 7.65 years) Crossover within-subject design |
N-back tasks Correct responses, reaction times |
Frontal cortex (F3) + subraorbital region Device: NeuroConn DC Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 40 Hz/tDCS/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode Size: both 5 × 7 cm Timing: online |
↗ (for 3-back condition when applied offline) − (with online-tACS, as well as for the 1- and 2-back condition) High risk (small sample size) |
Gamma and Theta | |||||
[77] |
Exp. 1 N = 20 (mean age: 21 years) Exp. 2 N = 20 (mean age: 23 years) Control 1 N = 20 (mean age: 23 years) Control 2 N = 20 (mean age: 23 years) Crossover within-subject design |
Visuo-spatial working memory task d′ |
Centro-to-temporal areas (CP1/T5) + right cheek Exp. 1 anti-phase between CP1 and T5 Exp. 2 in-phase between CP1 and T5 Control 1 in-phase between CP1 and T5 Control 2 anti-phase between CP1 and T5 Device: NeuroConn DC Stimulator MC (NeuroCare, Ilmenau, Germany) |
Frequency: Exp. 1/2: 40 Hz/sham; Control 1/2: 6 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode Size: both target electrodes 5 × 5 cm; return electrode 5 × 7 cm Timing: online |
↗ (with anti-phase gamma-tACS) − (with in-phase gamma-tACS or theta-tACS) Low risk |
Multiple Frequencies | |||||
[78] |
N = 25 (mean age: 69.1 ± 4.5 years) Exp. 1 no stimulation Exp. 2/3 Crossover within-subject design |
Retro-cue working memory paradigm Correct responses |
Parietal cortex (P3) + P4 |
Frequency: Exp. 1: no stimulation; Exp. 2: 4 Hz/10 Hz/40 Hz; Exp. 3: 10 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 20 min Electrode Size: both 5 × 7 cm Timing: online |
↗ (with alpha-tACS but only in Exp. 2, no replication in Exp. 3) − (with other tACS) Low risk |
Declarative memory | |||||
Theta | |||||
[79] |
N = 12 young (YA, mean age: 22.3 ± 1.5 years) N = 12 older adults (OA, mean age: 66.3 ± 3.9 years) Crossover within-subjects design |
Language-learning paradigm Correct responses |
Centro-parietal area (CP5) + supraorbital region Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: 6 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode size: target electrode 5 × 7 cm, return electrode 10 × 10 cm Timing: online |
↗ (in older adults) − (in younger adults) High risk (small sample size) |
[80] |
N = 72, (N = 24 for each experiment) Exp. 1 (mean age: 23.5 ± 3.1 years) Exp. 2 (mean age: 24.3 ± 2.9 years) Exp. 3 (mean age: 23.2 ± 2.2 years) Between-subject design |
Paired-associative learning task Correct responses |
Left temporal cortex (T7) + (FPz/T8) Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: 5 Hz modulated bursts of 80 Hz gamma/sham Intensity: 1 mA peak-to-baseline Duration: 10 min Electrode size: all 3 cm² Timing: online |
↘ (with gamma-bursts coupled with troughs of theta-waves) − (with every other coupling) Low |
[81] |
N = 28 (mean age: 71.2 ± 6.4 years) Crossover within-subject design |
Face-occupation task (Paired-associative learning) Correct responses |
Ventrolateral PFC (intersection of T3-F3 and F7-C3 and midpoint F7-F3) + supraorbital region Device: NeuroConn (NeuroCare, Ilmenau, Germany) |
Frequency: 5 Hz/sham Intensity: 1 mA peak-to-peak Duration: 20 min Electrode size: target electrode 5 × 7 cm, return electrode 10 × 10 cm Timing: online |
− Low risk |
[82] |
N = 25 (age range: 18–28 years) Crossover within-subjects design |
Short-term recognition task Correct responses Long-term memory recognition task Strength of recollection and familiarity |
Target stimulation: Right parietal cortex (P4) + (T8/C2/CP1/Oz) Active control: Left parietal cortex (P3) + (T7/C1/CP2/Oz) Device: Multi-channel stimulator (StarStim, Neuroelectrics, Barcelona, Spain) |
Frequency: 4 Hz/sham Intensity: 3 mA peak-to-peak Duration: 20 min Electrode size: 5 round-shaped electrodes with 1 cm radius Timing: online |
↗ (with theta-tACS; for familiarity) Low risk |
[83] |
N = 60 (age range: 18–45 years) N = 19 (mean age: 28.4 ± 6.9 years) N = 21 (mean age: 25.3 ± 5.6 years) N = 19 (mean age: 24.9 + 4.7 years) Between-subject design |
Visual associative memory task Correct responses |
Right fusiform cortex (P10) + (FP1/P2/P3/PO7) Device: Soterix MxN TES device (Soterix Medical Inc., New York, USA) |
Frequency: 6 Hz/sham Intensity: 2 mA peak-to-baseline Duration: 10 min Electrode size: HD-tES electrodes Timing: online |
↗ (accuracy and forgetting) Low risk |
Gamma | |||||
[84] |
N = 70 (mean age: 22.12 + 2.16 years) Congruent group 60-60 (N = 17) Congruent group 90-90 (N = 18) Incongruent group 60-90 (N = 17) Incongruent group 90-60 (N = 18) Between-subject design/Crossover within-subjects design |
Word-list learning Correct responses; d’; Reaction times |
Dorsolateral prefrontal cortex (F3) + left wrist Device: NeuroConn DC Brain Stimulator Plus (NeuroCare, Ilmenau, Germany) |
Frequency: 60 Hz/90 Hz/sham Intensity: 1.5 mA peak-to-peak Duration: 15 min during encoding, 15 min during retrieval Electrode size: both 5 × 7 cm Timing: online |
↗ (with the same gamma-tACS during encoding and retrieval) − (with different gamma-tACS during encoding and retrieval) Low risk |
[85] |
N = 36 (mean age: 21.3 ± 0.5 years) N = 18 (mean age: 21.2 ± 0.4 years) N = 18 (mean age: 21.3 ± 0.5 years) Between-subject design, mixed with repeated-measures within-subject design |
Episodic memory task (Word learning and recognition) Correct responses, d’, Reaction times |
PFC (F3) + left wrist Device: Eldith Brain Stimulator (NeuroCare, Ilmenau, Germany) |
Frequency: 60 Hz/sham Intensity: 0.75 mA peak-to-peak Duration: 15 min during encoding, 15 min during retrieval Electrode size: both 5 × 7 cm Timing: online |
↗ (accuracy) − (reaction times) Low risk |
[86] |
Exp. 1 N = 36 (mean age: 20.03 ± 2.38) Exp. 2 N = 36 (mean age: 20.97 ± 2.22) Crossover within-subject design |
Episodic memory task (Word and face learning and recognition) Correct responses |
Left IFG (FP1) + C5 Right IFG (FP2) + C6 Device: 4-channel DC Stimulator MC (NeuroCare, Ilmenau, Germany) |
Frequency: 18.5 Hz/control frequencies: 6.8 Hz, 10.7 Hz, 30 Hz, 48 Hz/sham Intensity: Exp. 1: 2 mA peak-to-peak Exp. 2: 1.6 mA peak-to-peak Duration: event-related stimulation for 2 s during each stimulus presentation (2 s × 360 = 720 s total stimulation duration) Electrode size: Exp. 1: 4 donut-shaped electrodes, each 14 cm2; Exp. 2: 4 round electrodes, each 10.75 cm2 Timing: online |
− Low risk |
Note. tACS, transcranial alternating current stimulation (HD-tACS, high-definition tACS); tDCS, transcranial direct current stimulation (HD-tDCS, high-definition tDCS); SMA, supplementary motor area; Exp., experiment; Hz, Hertz; IAF, individual alpha frequency; ITF, individual theta frequency; IBF, individual beta frequency; mA, Milliampere; min, minutes. Low risk bias = Sufficient sample size and control conditions (sham condition and/or control frequencies), description of blinding procedure and efficiency, randomization procedure described, detailed stimulation protocol and description of statistical analysis. High risk bias = Small sample size, no control parameters. Electrode positions were reported as follows: target electrode(s) + return electrode(s). The direction of the arrows indicates improvement (↗), decrease (↘), or no change (−) in performance with tACS.