Table 3.
Cognitive task measures (mean ± SD) extracted from studies
| Study | Cognitive task | Cognitive outcome measure | tDCS, mean ± SD | Sham, mean ± SD | Effect* |
|---|---|---|---|---|---|
| Measures of attention | |||||
| Allenby et al.65 | CPT | No. omission errors | 1.9 ± 4.3 | 2.1 ± 2.4 | Single |
| Breitling et al.67 | Flanker task (incongruent trials) | % Omission errors | 2.2 ± 4.6 | 5.8 ± 7.6 | Composite |
| Flanker task (incongruent trials) | Intraindividual coefficient of variation (ms)† | 0.2 ± 0.1 | 0.3 ± 0.1 | ||
| Cosmo et al.66 | Go/no-go task (fruits) | No. omission errors (post/pre)‡ | −2.9 ± 24.5 | −3.7 ± 21.2 | Single |
| Jacoby et al.42 | MOXO task | RT (ms) with 1 distractor | 552.2 ± 53.9 | 558.9 ± 52.1 | Composite |
| MOXO task | RT (ms) with 2 distractors | 556.5 ± 54.4 | 568.9 ± 53.5 | ||
| MOXO task | No. omission errors | 4.2 ± 4.1 | 4.3 ± 4.0 | ||
| Munz et al.60 | Alertness task | Intrasubject RTV (ms) | 69.5 ± 25.1 | 76.1 ± 31.2 | Composite |
| Go/no-go task (go trials) | Intrasubject RTV (ms) | 225.2 ± 246.9 | 379.4 ± 425.3 | ||
| Go/no-go task (go trials) | No. omission errors | 3.0 ± 3.0 | 4.3 ± 4.4 | ||
| Nejati et al.68 (experiment 1) | Go/no-go task (go trials) | % Correct | 93.3 ± 11.4 | 90.9 ± 19.6 | Composite |
| N-back task (1-back) | No. correct | 15.3 ± 8.3 | 14.4 ± 7.4 | ||
| WCST | No. of categories completed | 2.5 ± 0.8 | 2.4 ± 1.1 | ||
| WCST | No. total errors | 29.7 ± 8.3 | 30.7 ± 9.3 | ||
| Nejati et al.68 (experiment 2) | Go/no-go task (go trials) | % Correct | 100 ± 0.0 | 98.5 ± 3.2 | Composite |
| N-back task (1-back) | No. correct | 21.0 ± 2.3 | 17.9 ± 2.9 | ||
| WCST | No. of categories completed | 5.1 ± 0.7 | 3.9 ± 0.7 | ||
| WCST | No. total errors | 11.0 ± 2.9 | 21.6 ± 5.4 | ||
| Prehn-Kristensen et al.61 | Digit span task | No. correct | 9.6 ± 2.4 | 10.8 ± 2.1 | Single |
| Soff et al.62 | QbTest (inattention) | z-scores (omission errors, RT and intrasubject RTV) | 0.1 ± 1.2 | −0.1 ± 0.4 | Single |
| Soltaninejad et al.64 | Go/no-go task (go trials) | % Correct | 98.8 ± 3.6 | 98.9 ± 1.9 | Single |
| Soltaninejad et al.43 | Go/no-go task (go trials)§ | % Correct | — | — | Single |
| Sotnikova et al.63 | QbTest (overall) | Intrasubject RTV (ms) | 214.3 ± 97.2 | 235.2 ± 122.7 | Composite |
| QbTest (overall) | No. omission errors | 38.6 ± 22.8 | 22.5 ± 15.3 | ||
| QbTest (overall) | % Correct¶ | 31.7 ± 5.1 | 43.5 ± 6.9 | ||
| Measures of inhibition | |||||
| Allenby et al.65 | CPT | No. commission errors | 17.1 ± 9.1 | 19.8 ± 10.9 | Composite |
| Stop task | Stop signal RT | 288.4 ± 76.0 | 291.5 ± 68.1 | ||
| Breitling et al.67 | Flanker task (incongruent trials) | RT (ms) | 581.0 ± 43.0 | 585.0 ± 38.0 | Composite |
| Flanker task (incongruent trials) | % Errors | 9.8 ± 7.2 | 20.6 ± 9.2 | ||
| Cosmo et al.66 | Go/no-go task (fruits) | No. commission errors (post/pre)‡ | −5.5 ± 10.0 | −6.9 ± 10.4 | Single |
| Jacoby et al.42 | MOXO task | Multi-button responses | 4.7 ± 4.9 | 7.0 ± 6.3 | Composite |
| MOXO task | No. commission errors | 11.3 ± 11.2 | 11.7 ± 12.1 | ||
| Munz et al.60 | Go/no-go task (no-go trials) | No. commission errors | 15.7 ± 10.3 | 12.6 ± 8.2 | Single |
| Nejati et al.68 (experiment 1) | Go/no-go task (no-go trials) | % correct | 19.9 ± 7.6 | 19.0 ± 7.8 | Composite |
| Stroop task (incongruent trials) | RT (ms) | 2870 ± 2210 | 1390 ± 440 | ||
| Stroop task (incongruent trials) | % Errors | 24.9 ± 12.0 | 34.9 ± 15.5 | ||
| WCST | No. perseverative errors | 17.6 ± 3.6 | 18.0 ± 9.0 | ||
| Nejati et al.68 (experiment 2) | Go/no-go task (no-go trials) | % Correct | 22.7 ± 1.3 | 20.7 ± 4.4 | Composite |
| WCST | No. perseverative errors | 7.8 ± 2.4 | 14.8 ± 3.7 | ||
| Soff et al.62 | QbTest (impulsivity) | z-scores (commission errors, multi-button press per stimulus, anticipatory button press) | 0.2 ± 1.2 | −0.2 ± 0.7 | Single |
| Soltaninejad et al.64 | Go/no-go task (no-go trials) | % Correct | 96.2 ± 8.2 | 95.8 ± 6.9 | Composite |
| Stroop task (incongruent trials) | % Correct | 98.3 ± 2.9 | 96.4 ± 3.6 | ||
| Stroop task (incongruent trials) | RT (ms) | 1080 ± 180 | 1130 ± 220 | ||
| Soltaninejad et al.43 | Go/no-go task (no-go trials)§ | % Correct | — | — | Composite |
| Stroop task (incongruent trials)§ | % Correct | — | — | ||
| Stroop task (incongruent trials)§ | RT (ms) | — | — | ||
| Sotnikova et al.63 | QbTest (overall) | No. commission errors | 6.0 ± 5.1 | 6.0 ± 4.2 | Single |
| Measures of processing speed | |||||
| Allenby et al.65 | CPT | RT (ms) to target | 420.9 ± 63.3 | 419.7 ± 73.0 | Single |
| Jacoby et al.42 | MOXO task | RT (ms) to target | 541.5 ± 50.8 | 547.0 ± 53.5 | Composite |
| Munz et al.60 | Alertness task | RT (ms) | 309.6 ± 51.8 | 302.4 ± 44.3 | Composite |
| Go/no-go task (go trials) | RT (ms) | 453.2 ± 131.3 | 566.9 ± 234.1 | ||
| Nejati et al.68 (experiment 1) | Go/no-go task (go trials) | RT (ms) | 1080 ± 210 | 1030 ± 170 | Composite |
| N-back task (1-back) | RT (ms) | 120.2 ± 22.5 | 175.7 ± 55.4 | ||
| WCST | Completion time (ms) | 237 300 ± 79 800 | 291 100 ± 106 700 | ||
| Nejati et al.68 (experiment 2) | Go/no-go task (go trials) | RT (ms) | 1330 ± 900 | 1230 ± 120 | Composite |
| N-back task (1-back) | RT (ms) | 103.4 ± 24.2 | 162.9 ± 94.4 | ||
| WCST | Completion time (ms) | 123 200 ± 16 900 | 170 300 ± 85 900 | ||
| Soltaninejad et al.64 | Go/no-go task (go trials) | RT (ms) | 830 ± 290 | 910 ± 350 | Single |
| Soltaninejad et al.43 | Go/no-go task (go trials)§ | RT (ms) | — | — | Single |
| Sotnikova et al.63 | QbTest (overall) | RT (ms) | 555.3 ± 116.2 | 564.2 ± 130.8 | Single |
CPT = continuous performance task; QbTest = Quantitative Behaviour Test; RT = reaction time; RTV = reaction time variability; SD = standard deviation of the mean; Stroop = Stroop colour word task; WCST = Wisconsin Card Sorting Task.
*
For multiple effects from the sample, we created composite effect-size estimates; single effects otherwise.
†
Intrasubject reaction time variability divided by mean reaction time.
‡
Only change scores (post – pre/baseline) were reported.
§
The author could not provide raw means and standard deviations for each stimulation condition, so to calculate Hedges’ g we converted the reported t-statistics.57
¶
The % correct was reported as: hits (total no. of target trials – no. of omission errors errors) + correct rejections (total no. of no-go trials – no. of commissions errors)/total number of stimuli63