(age ) Crossover design (tACS versus tDCS versus sham)
Executive function/working memory 2- and 3-back task before and after stimulation Change in -primes and accurate RT
F3 + R supraorbital
Frequency: 40 Hz (tACS); NA (tDCS) Intensity: 1.5 mA peak-to-peak amplitude (tACS); 2 mA (tDCS) Duration: 20 min Electrode size: both 5 × 7 cm2 Timing: task (2-back)
Selective improvement on 3-back after gamma-tACS compared to tDCS and sham No effects of RT #Offline-effects
Role of frontal gamma-tACS in neuromodulation Preliminarily evidence for gamma-tACS preferentially improving working memory performance at higher loads
in P3 and in P4 and in F3 tACS group (age ) Crossover within-group design (tACS versus sham)
Executive function/working memory Corsi-block tapping, digit span (both forward and backward), and -back Span core and number of correct responses
P3 (L), P4 (R), or F3 (L) + R supraorbital (Fp2)
Frequency: 5 ± 1 Hz (based on individual alpha peak minus 5 Hz) Intensity: 1–2.2 mA (based on individual skin sensations) Duration: 15 min Electrode size: both 5 × 7 cm2 Timing: rest
Increased capacity score after L and R parietal tACS, but not frontal, compared to sham More pronounced effect of L parietal tACS on backward compared to forward recall #Offline-effects
Central role of parietal areas for working memory storage capacity
in tACS and in sham (age 19–27) Between-subjects design
Executive function/working memory Verbal working memory task (2-back task with word pairs) and rating of success-confidence on task Accuracy and self-evaluation scores
L DLPFC (F3/AF3 midpoint) + R DLPFC (F4/AF4 midpoint)
in parietal and in frontal tACS group (age ) Crossover within-group design (tACS versus sham)
Executive function/cognitive control/fluid intelligence (problem-solving and visual-spatial reasoning) Progressive matrices, paper folding, and cutting test EEG frequency spectra and performance test scores
L parietal (P3) or L frontal (F3) + R supraorbital (Fp2)
Frequency: 5 ± 1 Hz (based on individual alpha peak minus 5 Hz) Intensity: 1–2.2 mA (based on individual skin sensations) Duration: 15 min Electrode size: 5 × 7 cm2 (P3/F3) and 7 × 10 cm2 (Fp2) Timing: rest
Increased resting EEG theta power and decreased EEG alpha power after theta-tACS Improved test scores after tACS Behavioral effect more pronounced in L parietal tACS group (better in both tests) compared to L frontal #Offline-effects
Influence of brain oscillatory activity by theta-tACS Importance of parietal regions for fluid intelligence Parietal tACS increased working memory storage capacity and frontal tACS influenced attentional components
(age ) in Exp. 1 and (age ) in Exp. 2 Crossover within-group design (3 conditions in Exp. 1: sham, theta-, and gamma-tACS; 3 conditions in Exp. 2: sham, tRNS, and gamma)
Executive function/cognitive control/fluid intelligence and working memory Abstract-reasoning task (progressive matrices), delayed-match-to-sample (change-localization) task, and control task (odd-even numbers) RT and accuracy
L MFG (−34, 16, and 30) + Cz
Frequency: 5, 40 Hz (Exp. 1); 5, 101–640 Hz tRNS (Exp. 2) Intensity: .75 mA peak-to-peak amplitude Duration: 30 min Electrode size: 5 × 5 cm2 Timing: task (visuospatial reasoning and working memory)
Shortening of RT to solve complex logic problem in gamma-tACS condition compared to all other conditions in both Exp. 1 and Exp. 2 Greater tACS-induced enhancement for slower participants No effect in theta-tACS or tRNS No effect on working memory task #Online-effects
Frequency-specific neuromodulatory effects on cognitive ability Individual differences in gamma-tACS responsiveness
in L, in R, and in sham Between-subjects design (3 groups: L, R, and sham)
Executive function/cognitive control/decision-making Balloon Analog Risk Task Number of pumps and total number of balloon explosions
L DLPFC (F3) + L temporal (CP5)/R DLPFC (F4) + R temporal (CP6)
Frequency: 6.5 Hz Intensity: 1 mA peak-to-peak amplitude Duration: 15 min Electrode size: all 5 × 5 cm2 Timing: task (decision-making)
Riskier decision-making in L-tACS group compared to R-tACS and sham group No difference between sham and R-tACS groups #Online-effects
Theta-band oscillatory and DLPFC activity critical for decision-making Disruption of ability to process and adjust actions based on negative feedback and errors by theta-tACS
(age 19–31) Crossover design (theta- versus alpha-tACS)
Executive function/cognitive control/conflict processing Spatial response conflict task (color-location Simon task) RT and accuracy
Centered between FCz/Cz bilaterally on cheeks (reference electrodes)
Frequency: 8–12 versus 4–8 Hz (based on individual alpha and theta peak) Intensity: 2 mA peak-to-peak amplitude Duration: ~20 min Electrode size: 9 cm2 (FCz/Cz) and 35 cm2 (cheeks) Timing: task (spatial conflict)
Slower RTs and lower accuracy for high conflict trials: conflict reduced during tACS Effect driven by slower RTs in low-conflict trials #Online-effects
Modulation of cognitive control through theta-tACS
in tACS and in sham group (age ) Between-subjects design
Executive function/working memory (WM) and short-term memory (STM) Digit span backward and 3-back task (both WM) and digit span forward (STM) EEG frequency spectra, mean list length (digit span task), and accuracy (3-back task)
FPz + Pz
Frequency: ~3.7–4.6 Hz (below individual theta frequency) Intensity: ~.4–1.3 mA (below individual phosphene or perception threshold) Duration: 18 min Electrode size: all 5 × 7 cm2 Timing: task (digit span)
Increased digit span forward during stimulation in tACS group No effect in digit span backward and 3-back accuracy No effect beyond the stimulation period Increase in theta-amplitude after stimulation in tACS group #Online- + offline-effects
Successful manipulation of theta frequencies caused increase in STM capacity
