Table 2.
Clinical and cognitive effects of sham-controlled tDCS studies.
| Stimulation Protocol | Outcome Measures (Bold/Underlined = Improvement; Cursive = Impairment) |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Study | Design | n | Mean Age | Anode/Cathode | mA | Sessions | Timing a | Duration (mins) | Clinical | Cognitive |
| Children | ||||||||||
| † Bandeira et al., 2016 [168] |
Open label | 9 | 11 | L DLPFC/R SOA | 2 | 5 | Online | 28 | Patient Global Impression of Improvement | Visual Attention Test (OM); NEPSY-II-inhibition (Switch errors); Digit Span; Corsi Cubes |
| Breitling et al., 2016 [169] |
Single-blind, sham-controlled, randomised, crossover | 21 | 14 | R IFC/L Cheek | 1 | 1 | Online | 20 | n/t | Flanker (Incongruent trials: COM c,d & RTV c) e |
| L Cheek/R IFC | 1 | 1 | Online | 20 | n/t | Flanker | ||||
| Munz et al., 2015 [167] |
Double-blind, sham-controlled, randomised, crossover | 14 | 12 | L DLPFC/R Cheek; R DLPFC/L Cheek |
0.25 | 1 | Offline | 25 (5 on, 1 off) | n/t | Go/No-Go (Go RT & RTV); Motor memory; Alertness |
| Nejati et al., 2020, Exp 1 [171] |
Double-blind, sham-controlled, randomised, crossover | 15 | 10 | L DLPFC/R DLPFC | 1 | 1 | Offline | 15 | n/t | Go/No-Go; N-back (Acc, RT); Stroop (Incongruent trials: COM & RT); WCST (Completion time) |
| Nejati et al., 2020, Exp 2 [171] |
Double-blind, sham-controlled, randomised, crossover | 10 | 9 | L DLPFC/R SOA | 1 | 1 | Offline | 15 | n/t | Go/No-Go; N-back (Acc c, RT) d; WCST (Total categories completed, total & pers errors) d |
| R SOA/L DLPFC | 1 | 1 | Offline | 15 | n/t | Go/No-Go (No--Go acc) d; N-back; WCST (Total categories completed, total & pers errors c) d | ||||
| Prehn-Kristensen et al., 2014 [166] |
Double-blind, sham-controlled, randomised, parallel | 12 | 12 | L DLPFC/R Cheek; R DLPFC/L Cheek | 0.25 | 1 | Offline | 25 (5 on, 1 off) | n/t | Declarative Memory (Acc); Alertness; Digit Span |
| Soff et al., 2017 [164] |
Double-blind, sham-controlled, randomised, crossover | 15 | 14 | L DLPFC/Vertex | 1 | 5 | Online | 20 | FBB-ADHD(Inattention f) g,h | QbTest (Inattention f; hyperactivity i) g,h |
| Soltaninejad et al., 2019 [161] | Single-blind, sham-controlled, randomised, crossover | 20 | 16 | L DLPFC/R SOA | 1.5 | 1 | Online | 15 | n/t | Go/No-Go (Go Acc) c,d; Stroop |
| R SOA/L DLPFC | 1.5 | 1 | Online | 15 | n/t | Go/No-Go (NoGo Acc) c,j; Stroop | ||||
| ‡ Soltaninejad et al., 2015 [161] |
Single-blind, sham-controlled, randomised, crossover | 20 | 16 | rIFC/L SOA | 1 | 1 | Online | 15 | n/t | Go/No-Go (Go Acc); Stroop |
| Sotnikova et al., 2017 [165] |
Double-blind, sham-controlled, randomised, crossover | 13 | 14 | L DLPFC/Vertex | 1 | 1 | Online | 20 | n/t | QbTest (RT, RTV k, OMs, Acc) l |
| Breitling et al., 2020 [169] |
Double-blind, sham- and HD-tDCS controlled, randomised, crossover | ADHD: 15HC: 15 | 13 (10–16) |
R IFC/L SOA | 1 | 3 with CT | Online | 20 | n/t | WM task; ERPs N200; P300 |
| Salehinejad et al., 2020 [170] |
Single-blind, sham-controlled, randomised, cross-over | 19 | 9 (8–12) |
1 | 2 | Online | 23 | n/t | ANT (orienting); GNG; SAT; Stroop | |
| † Westwood et al., 2021 [162] |
Double-blind, sham-controlled, randomised, parallel | 50 | 14 | R IFC/L SOA | 1 | 15 | Online | 20 | ADHD-RS; Conners 3P | GNG; Stop; Simon; WCST; CPT; MCT; time estimation; NIH WM; Verbal Fluency |
| Nejati et al., 2020 [171] |
Double-blind, sham-controlled, randomised, cross-over | 20 | 9 | L DLPFC/R vmPFC R DLPFC/L vmPFC Sham |
1 | 1 | Online | 20 | n/t | BART; CDDT (k20, k10) |
| † Berger et al., 2021 [174] |
Double-blind, active controlled, randomised, cross-over | 19 | 7–12 | L DLPFC (tDCS)/R SOA L DLPFC/R IFC (tRNS) |
0.75 | 5 | Online | 5 | n/t | ADHD-RS; Working & short-term memory, Moxo-CPT (all improved with tRNS vs. tDCS) |
| Adults | ||||||||||
| † Allenby et al., 2018 [177] |
Double-blind, sham-controlled, randomised, crossover | 37 | 32 | L DLPFC/R SOA | 2 | 3 | Online | 20 | n/t | Conners CPT (COM m); Stop Task |
| Cachoeira et al., 2017 [178] |
Double-blind, sham-controlled, randomised, parallel | A: 9 S: 8 |
A: 31 S: 34 |
R DLPFC/L DLPFC | 2 | 5 | Offline | 20 | ADHD Checklist (Inattention, Total) n; SDS (after tDCS); ADHD total score 2 weeks | None |
| Cosmo et al., 2015 [175] |
Double-blind, sham-controlled, randomised, parallel | A: 30 S: 30 |
A: 32 S: 33 |
LDLPFC/R DLPFC | 1 | 1 | Offline | 20 | n/t | Go/No-Go |
| Jacoby et al., 2018 [176] |
Single-blind, sham-controlled, randomised, crossover | 20 | 23 | L&R DLPFC/Cerebellum | 1.8 | 1 | Offline | 20 | n/t | CPT (multi-button presses) |
| Dubreuil-Vall et al., 2020 [179] |
Double-blind, sham-controlled, randomised, crossover | 37 | 18–67 | L DLPFC/R SOA R DLPFC/R SOA |
2 | 1 | Offline | 30 | n/t | Flanker (incongruent RT) n = 18; L P300; L N200. Stop (go RTs); L P200. n = 19 Flanker; Stop |
Abbreviations: A, active; Acc, accuracy; ANT, attention networking task; BAART, Balloon analogue risk taking task; CDDT, chocolate delay discounting task; COMs, commission errors; Conners 3P, Conners-3 Parent Rating Scale; CPT, continuous performance task; DLPFC, dorsolateral prefrontal cortex; FBB-ADHD, parents’ version of a German adaptive Diagnostic checklist for ADHD; L, left; mA, milliamps; mins, minutes; n/t, not tested; OMs, omission errors; cM, contralateral mastoid relative the other electrode; SOA, contralateral supraorbital area relative the other electrode; IFC, inferior frontal cortex; MCT: Mackworth Clock Task; NIH-WM, NIH Toolbox List Sorting Working Memory Test; N200; negative ERP component; P300; positive ERP component; R, right; RT, reaction time; RTV, reaction time variability or standard deviation of reaction times; S, sham; SAT, switching attention task; SDS, Sheehan Disability Scale; SSRT, stop-signal reaction time; WCST, Wisconsin task-sorting task. a Timing refers to whether cognitive performance was during (online) or after (offline) stimulation; c Would likely not survive multiple comparison correction; d Comparisons between stimulation conditions based on post-hoc LSD tests, which do not correct for multiple comparisons; e Based on underpowered analysis focusing on the first session, with seven participants per condition; f Improvement only seen seven days after the fifth anodal tDCS session; g Did not survive correction for multiple comparisons; h Based on underpowered analysis focusing on the first five sessions, with seven/eight participants per condition; i Improvement seen immediately after the fifth anodal tDCS session and seven days later; j Significant in comparison to cathodal tDCS only; k Based on a crossover interaction. tDCS reduced RT and RTV in one out of four conditions (2-back tasks), but this did not survive correction for multiple comparisons; l Included carryover effect raised by Soff et al., (2017); m Significant only immediately after anodal tDCS, not significant three days later; n Inattention improved immediately after anodal tDCS and after two weeks, while total score improved only after two weeks. † combined stimulation with cognitive training; ‡ originally published written in Persian language but was translated for us by the lead author Dr Zahra Soltaninejad.