Table 1.
Characteristics and findings of clinical studies assessing the effects of tDCS in ADHD
| Stimulation Protocol | ||||||||
|---|---|---|---|---|---|---|---|---|
| Study | Population | Montage* | Current intensity (density)/duration | tDCS design | Number of sessions | Results | Adverse events | Conclusions |
|
Cosmo et al. (Cosmo et al., 2015a; Cosmo et al., 2015b) |
60 adults with ADHD |
Anode: L DLPFC (F3) Cathode: R DLPFC (F4) |
1mA (0.03mA/cm2) 20 minutes |
Offline |
1 active 1 sham |
A statistically significant difference was found comparing the weighted node degree prior to and following active tDCS, in the electrodes located over left DLPFC and correlated areas No significant differences between tDCS and sham groups in the Go/No-Go tasks |
None |
Anodal tDCS increased functional brain connectivity in individuals with ADHD compared to baseline resting state No improvement in inhibitory control by tDCS application over L DLPFC |
| Breitling et al. (Breitling et al., 2016) | 21 adolescents with ADHD and 21 healthy controls |
Experiment 1:
Anode: R IFG (F8) Cathode: posterior to L mastoid Experiment 2: Anode: posterior to L mastoid Cathode: R IFG (F8) |
1mA (0.03mA/cm2) 20min |
Online | 2 active 1 sham |
Reduction in commission errors and variability in RT in the modified Eriksen Flanker tasks after anodal stimulation, when compared to sham | Skin sensations | Improved interference control following anodal tDCS over R inferior frontal gyrus |
| Bandeira et al. (Bandeira et al., 2016) | 9 children and adolescents with ADHD | Anode: L DLPFC (F3) Cathode: R supraorbital area (Fp2) |
2mA (0.06mA/cm2) 30 minutes |
Online | 5 active |
Decrease in errors by omission in TAVIS-3, as well as in uncorrected and total errors in switching task and completion time in the naming task of the NEPSY-II, when comparing post and pre intervention results. No significant differences in the Digit Span subtest of the WISC-III | Mild and moderate tingling, itching and burning sensation. Sense of shock, mild headache, neck pain, local redness and mild sleepiness | Anodal tDCS enhanced selective attention and inhibitory control after 5 sessions. |
| Nejati et al. (Nejati et al., 2017) | 25 children with ADHD Experiment 1 (N=15) Experiment 2 (N=10) |
Experiment 1: Anode: L DLPFC (F3) Cathode: R DLPFC (F4) Experiment 2: Montage 1: Anode: L DLPFC (F3) Cathode: R OFC (Fp2) Montage 2: Anode: R OFC (Fp2) Cathode: L DLPFC (F3) |
1mA (0.04mA/cm2) 15min |
Offline |
Experiment 1: 1 active 1 sham Experiment 2: 2 active 1 sham |
Improved N-back test performance in both experiments when anodal tDCS was applied over L DLPFC Experiment 1: improved interference response inhibition. No differences on Go/No-Go and WCST Experiment 2: improved performance on Go/No-Go with montage 2, and on WCST for both montages (more pronounced in the montage 1) |
Mild side effects (itching and tingling) | Anodal L DLPFC stimulation improved working memory. Anodal tDCS over L DLPFC and cathodal on R DLPFC enhanced interference response inhibition Increased inhibitory control and cognitive flexibility were seen after anodal stimulation over R OFC |
| Soff et al. (Soff et al., 2017) | 15 adolescents with ADHD | Anode: L DLPFC (F3) Cathode: vertex (Cz) |
1mA Anode (0.08mA/cm2) Cathode (0.29mA/cm2) 20min |
Online | 5 active 5 sham |
Improvement in clinical parameters of inattention, impulsivity, and Qb-test after tDCS, when compared to sham | Mild side effects (tingling and itching) | Anodal tDCS caused a significant reduction in clinical symptoms of inattention and impulsivity. It also improved hyperactivity, with a more robust reduction seen by the 7th day following the treatment |
| Sotnikova et al. (Sotnikova et al., 2017) | 16 adolescents with ADHD | Anode: L DLPFC (F3) Cathode: vertex (Cz). |
1mA Anode (0.29mA/cm2) Cathode (0.08mA/cm2) 20min |
Online | 1 session | Improvement in RT in the working memory paradigm in the active group More omission errors and less accuracy in the active group, when compared to sham Increase in connectivity and neuronal activation in the L DLPFC and surrounding regions in the active group |
Mild side effects (tingling and itching) | Anodal stimulation over L DLPFC improved motor performance, but worsened accuracy in the working memory paradigm Anodal tDCS increased neuronal activation and connectivity in the L DLPFC with propagation to L premotor cortex, L supplementary motor area and precuneus |
| Cachoeira et al. (Cachoeira et al., 2017) | 17 adults with ADHD | Anode: R DLPFC (F4) Cathode: L DLPFC (F3) |
2 mA (0.06mA/cm2) 20 minutes |
Offline | 5 active 5 sham |
Significant lower ASRS inattention and SDS scores after active tDCS, compared to sham |
Tingling, itching, burning sensation, headache, fatigue, anxiety, visual symptoms, nausea, insomnia and acute mood change | Anodal tDCS over R DLPFC significantly improved attention and functional impairment, but not hyperactivity/impulsivity |
| Jacoby and Lavidor (Jacoby and Lavidor, 2018) | 21 adults with ADHD/ 16 healthy controls | Anode: L and R DLPFC (F3 and F4) Cathode: cerebellum |
1.8mA Anode (0.2mA/cm2) Cathode (0.05mA/cm2) 20 minutes |
Offline | 1 active 1 sham |
No tDCS effects in most MOXO-CPT domains, except for hyperactivity | None | Double anodal prefrontal tDCS reduced hyperactivity, however no effects were observed in attention and impulsivity domains |
| Allenby et al. (Allenby et al., 2018) | 37 adults with ADHD | Anode: L DLPFC (F3) Cathode: R supra-orbital area (Fp2) |
2mA (0.08mA/cm2) 20 minutes |
Online | 2 periods (active vs. sham) of 3 sessions | Decrease in false positive errors on CPT before and immediately after active tDCS No significant improvement in SST performance following active tDCS |
Mild side effects (mostly itching, burning and tingling) | Repeated anodal tDCS over L DLPFC improved impulsivity, however the effects were transient (< 3 days) |
| Soltaninejad et al. (Soltaninejad et al., 2019) | 20 adolescents with ADHD |
Experiment 1: Anode: L DLPFC (F3) Cathode: R supraorbital area (Fp2) Experiment 2: Anode: R supraorbital area (Fp2) Cathode: L DLPFC (F3) |
1.5mA (0.04mA/ cm2) 15 minutes |
Online | 2 active 1 sham |
Cathodal tDCS and anodal stimulation over the L DLPFC enhanced inhibition accuracy and prepotent response inhibition in the Go/No-Go task, respectively No significant difference was seen in interference inhibition measured by the Stroop task |
None. Reported in methods, but no results available | tDCS over the left DLPFC improved inhibitory control |
*
Stimulated areas are described in accordance with the 10–20 International EEG system.
ADHD: attention-deficit/hyperactivity disorder; tDCS: transcranial direct current stimulation; L: left; R: right; DLPFC: dorsolateral prefrontal cortex; OFC: orbitofrontal cortex; IFG: inferior frontal gyrus; RT: reaction time; ASRS: Adult ADHD Self-Report Scale Symptom; WISC-III: Wechsler Intelligence Scale for Children; NEPSY-II: Neuropsychological Development Assessment; TAVIS-3: Visual Attention Test; WCST: Wisconsin Card Sorting Test; Qb-Test: Quantified Behavioral Test; SDS: Sheehan Disability Scale; CPT: Conners’ Continuous Performance Task; SST: Stop Signal Task; MOXO-CPT: MOXO Continuous Performance Test.