Transcranial stimulation (+)

According to the majority opinion, there are predominantly indications of a positive effect ^{1 23}
One small study found improvements from transcranial stimulation in terms of improvements in ADHD, which were further enhanced when combined with cognitive training.⁴

Other sources speak of mixed results.⁵

• 1. Transcranial direct current stimulation (tDCS) for ADHD
• 2. Transcranial magnetic stimulation (tDMS / rtDMS / rTMS) for ADHD
• 3. Transcranial alternating current stimulation (tACS) for ADHD
• 4. Transcranial photobiomodulation (tPBM) for ADHD
• 5. Transcranial random noise stimulation (tRNS) for ADHD

1. Transcranial direct current stimulation (tDCS) for ADHD¶

METASTUDIES

• A meta-analysis of 17 trials from k = 13 studies with n = 582 subjects found improvements in various symptoms (see below).⁶
• A meta-analysis found a significant positive effect in 8 (n = 133) of 13 studies (n = 308) rather in children and adolescents for inattention, impulsivity and the general level of symptoms, with a delayed onset of effect in relation to hyperactivity⁷
• Another meta-analysis found significant improvements in attention, inhibition, working memory and brain connectivity in k = 11 studies.⁸
• A meta-analysis found evidence of improvements in certain cognitive functions, ADHD symptoms and improvement in sleep parameters in 5 trials, with reduced efficacy results due to high heterogeneity in trial protocols.⁹

Conclusion: The results show limited evidence; however, it is hypothesized that the combined use of non-invasive stimulation with other approaches, such as cognitive training, may improve the effect of the intervention. It is also important to consider limitations such as heterogeneity of clinical protocols, selection of participants with ADHD, including dosage and frequency. These factors should be investigated in future research to optimize the use of these therapies.

Other sources found tDMC to be helpful for ADHD.¹⁰ Transcranial direct current stimulation was found to be more effective than repetitive transcranial magnetic stimulation for ADHD in one review.¹¹ One positive review attracted unpleasant attention due to questionable and unsubstantiated statements (tDMC would be more effective than stimulants; alleged lack of studies on the long-term safety of stimulants).¹²

Effect of transcranial direct current stimulation (tDCS) on individual symptoms:

• Attention
  • 0.66 SMD (meta-analysis, 8 trials from k = 7 studies with n = 277 subjects)⁶
  • Attention improved, but not overall ADHD scores in children and adolescents with ADHD¹³
  • Improved attention in the school context¹⁴
  • Maintenance of effort improved¹⁵
• Inhibition
  • 0.21 SMD (meta-analysis, 17 trials from k = 13 studies with n = 582 subjects)⁶
  • 0.18, statistically not significant (meta-analysis, 12 tests in k = 11 studies)¹⁶
• Working memory
  • 0.31 SMD (meta-analysis, 12 trials from k = 9 studies with n = 390 subjects)⁶
• Cognitive flexibility
  • 0.61 SMD statistically not significant (meta-analysis, 4 trials from k = 2 studies with n = 94 subjects)⁶
• Hyperactivity
  • 0.41 SMD statistically not significant (meta-analysis, 4 trials from k = 4 studies with n = 94 subjects)⁶
• Inhibition
  • 0.21, statistically just not significant (meta-analysis, 11 tests in k = 10 studies)¹⁶
• Risk assessment and reward discounting improved ¹⁷
• ASS
  • A review of rDCS in children up to 9 years of age found k = 8 studies, all of which involved children with ASD. Anodal tDCS, mainly targeting the left dlPFC, showed positive effects on reducing ASD symptoms. tDCS was found to be safe and partially effective, but long-term effects of tDCS and changes in connectivity during tDCS in autism were not demonstrated.¹⁸
• Time processing
  • Anode on dlPFC left / cathode on vmPFC right; anode on dlPFC right / cathode on vmPFC left; anode dlPFC left isolated; right vmPFC stimulation with extracranial counter electrodes all improved time discrimination to the same extent compared to sham stimulation¹⁹
  • Anode on dlPFC right / cathode on vmPFC left; anode dlPFC isolated; isolated vmPFC stimulation with extracranial counter electrodes improved time reproduction but not time estimation compared to sham stimulation¹⁹
• Working speed
  • 0.14, statistically just not significant (meta-analysis, 8 tests in k = 7 studies)¹⁶
• Emotion regulation
  • one study found a statistically significant improvement in emotion regulation through tDCS, two studies found no statistically significant influence (meta-analysis, k = 3)²⁰

One study found evidence of increased (extracellular) dopamine levels in the striatum during or after frontal tDCS application²¹

One study reported that the smaller the following brain regions were, the better the effect of tDCS on inattention:²²

• left dlPFC
• middle frontal gyrus
• inferior frontal gyrus
• left ACC supragenual

Other sources speak of mixed results.²³²⁴

One study found no improvement with transcranial direct current treatment over the left dorsolateral PFC.²⁵

2. Transcranial magnetic stimulation (tDMS / rtDMS / rTMS) for ADHD¶

Various studies have looked at the effect of transcranial stimulation on ADHD.^26272829

A small study reports a better effect of repetitive transcranial magnetic stimulation compared to other non-pharmacological treatment for ADHD.³⁰ The treatment group showed improved resting-state functional connectivity in the left and right dlPFC and in the left and right mPFC. Resting-state functional connectivity in the left and right temporal lobe was not improved. In the Go/No-Go task, mean HbO2 concentrations were increased in the left and right dlPFC and in the left and right mPFC and were unchanged in the left and right temporal lobe.
One study reports a better effect of repetitive TMS application on ADHD than with the antipsychotic Tiapride. A combination further improved the effect.³¹
Nevertheless, we consider antipsychotics to be unsuitable for the treatment of ADHD.
One study found an improvement in impulse control in adults with ADHD, without quantifying this further.³²
A meta-analysis found no evidence of improvements in ADHD symptoms or sleep parameters.⁹

Other sources speak of mixed results.³³

Effect of transcranial magnetic stimulation (tDMS) on individual symptoms:

• Hyperactivity
  • Hyperactivity improved, but not attention (individual case of an adult with ADHD)³⁴³⁵
  • Hyperactivity/impulsivity improved at home¹⁴
  • 1 Hz rTMS over the left dlPFC improved hyperactivity/impulsivity (and inattention) in children with ADHD³⁶, unlike 10 Hz stimulation of the right dlPFC, which did not improve ADHD symptoms compared to sham stimulation³⁷
  • 0.04 SMD statistically not significant (meta-analysis, 4 trials from k = 3 studies with n = 137 subjects)⁶
• Attention
  • 1 Hz rTMS over the left dlPFC improved inattention (and hyperactivity/impulsivity) in children with ADHD³⁶, unlike 10 Hz stimulation of the right dlPFC, which did not improve ADHD symptoms compared to sham stimulation³⁷
  • Attention improved without improvement in mood, anxiety or hyperactivity in adults with ADHD³⁸
  • 0.04 SMD statistically not significant (meta-analysis, 4 trials from k = 3 studies with n = 137 subjects)⁶
• oppositional defiant behavior improved¹⁴
• Emotion regulation
  • two studies found no statistically significant improvement in emotion regulation with rTMS (meta-analysis, k = 2)²⁰

Two very small studies found evidence of increased (extracellular) dopamine levels in the striatum during and after TMS application.³⁹ The increase corresponded to that seen with the administration of D-amphetamine.⁴⁰

3. Transcranial alternating current stimulation (tACS) for ADHD¶

Improvements in ADHD have also been reported for transcranial alternating current stimulation (tACS).⁴¹⁴²

Effect of transcranial alternating current stimulation (tACS) on individual symptoms:

• Attention improved; fewer omission errors in people with ADHD, along with an improvement in P 300 amplitude⁴³
• Working memory improved by optimized high-resolution tACS with a frequency of 5 Hz above the left DLPFC⁴⁴

4. Transcranial photobiomodulation (tPBM) for ADHD¶

A study reports positive results from transcranial photobiomodulation (tPBM) for ADHD.⁴⁵

5. Transcranial random noise stimulation (tRNS) for ADHD¶

Transcranial random noise stimulation (tRNS) over the prefrontal cortex during a time perception task tended to improve the accuracy of time perception in the ADHD group and brought their performance closer to accurate time intervals. In contrast, the accuracy of time perception decreased in the healthy control group.⁴⁶