The Efficacy of Cathodal tDCS in ADHD
Condition: ADHD
Study type: Interventional

Summary: 
      The purpose of this study is to investigate the effectiveness of five sessions of cathodal
      tDCS over the left DLPFC on inhibitory control/response inhibition in children and
      adolescents with ADHD. Investigators hypothesize that multiple sessions of cathodal tDCS will
      induce a greater and long-term effect on inhibitory response in children and adolescents with
      ADHD.
    

Detailed description: 
      Attention-deficit hyperactivity disorder (ADHD) is one of neural development disorder that
      characterized by a persistent pattern of inattention, impulsivity and hyperactivity. This
      disorder begins in childhood and often lasts into adulthood. Rates of ADHD diagnosis have
      been rising in recent years, a prevalence estimates from 3-7% of childhood worldwide. A
      recent national prevalence shows that 8.1% of Thai primary school-age children are affected
      by ADHD . Pharmacological treatment used in ADHD is well-established, however, each patient
      responds to medication differently and treatment in some of them are limited by side effect
      and abuse of medication.

      In the last decade, transcranial direct current stimulation (tDCS) has received a surge of
      interest in clinical research since it could modulate cortical excitability and induce
      plasticity in human brain. The device sends a constant low direct current (e.g. 1-2 mA)
      delivered to the area of interest through the electrodes. This induces shifts in neuronal
      resting membrane potential changing cortical excitability. Based on the polarity-specific
      effects, anodal tDCS increases cortical excitability and cathodal tDCS decreases cortical
      excitability. To change the cortical excitability, tDCS differs from other brain stimulation
      techniques such as transcranial magnetic stimulation (TMS) in that it does not cause action
      potentials in cortical neurons, but rather induces shifts in neuronal resting membrane
      potential. This is considered to induce a lesser or no risk of a seizure. Given its
      advantages such as painlessness, safety, easiness to use, and low-cost, a number of tDCS
      studies has been increasing in the last decade particularly in motor rehabilitation and
      neuropsychiatric disorders such as depression, autism and schizophrenia with a positive and
      safety reports in adult and pediatric populations. Possible after-effect of tDCS has been
      also reported in motor and psychological disorders that opens a way to use tDCS as a
      therapeutic tool.

      The most accepted theory of neural basis of ADHD is deficient of inhibitory control resulting
      in executive dysfunction. Inhibitory control or response inhibition is key feature of
      self-control and can be defined as ability to inhibit prepotent actions. Several evidences
      reveal a physiological association between the prefrontal cortex and its subcortical
      connection with the pathophysiology of ADHD. Neuroimaging studies demonstrate that regions of
      the right dorso-lateral prefrontal cortex (DLPFC) play a role in the inhibition of motor
      response. During preforming an inhibitory task that is usually used to evaluate the
      efficiency of response inhibition such as stop-signal and go/no-go tasks, this area become
      active in healthy individual, while in ADHD showed hypo-activation compared to control.

      Evidences showed that the task performance in stop-signal and go/no-go tasks can be
      influenced by tDCS application to the DLPFC in healthy subjects. It was recently reported
      that a single session of cathodal tDCS, using a single session of 1.5 mA for 15 minutes over
      the left DLPFC improved their ability to inhibit themselves by do not response to no-go
      stimulus during go/no-go tasks compared to anodal and sham conditions in adolescents with
      ADHD. It was postulated that the inter-hemispheric inhibition (IHI) between two regions (left
      and right DLPFC) might play a role in this finding. Based on the possibility that cathodal
      stimulation decreases excitability and thus IHI drive from the left DLPFC is decreased,
      facilitating activity of the right DLPFC where is involved in inhibition of motor response as
      demonstrated by neuroimaging studies. Using a single session of oscillatory tDCS during early
      sleep, memory consolidation and reaction times in a go/no-go task were improved on the next
      day in children with ADHD. This is an argument to explore its possible therapeutic effect in
      long-term use. Five tDCS sessions for five consecutive days was reported to be safe and
      improves aspect of attention in children and adolescents with ADHD, however, its after-effect
      in this population is unknown. In patients with depressive disorder, multiple sessions of
      tDCS over the left DLPFC for five or ten days has been demonstrated to decrease depressive
      symptoms and lasted for a month. It was reported in patient with depressive disorder that
      after five days of tDCS sessions on alternative day did not show an improvement, positive
      results was observed after 10 days. This suggests that a longer observation period is
      probably required to detect a true tDCS effect.

      The use of electrophysiological techniques, especially of event-related potentials (ERP)
      measured by means of electroencephalography (EEG) allows for analysis of neural change
      accompanying inhibitory process in the brain. Two ERP components, the no-go N2 and P3 that
      are the most commonly studied in go/no-go tasks have been linked to response conflict and
      response inhibition. Studies have reported lower N2 and P3 amplitudes during go/no-go tasks
      in children and adolescents with ADHD.

      To expand current information on tDCS as an emerging treatment for ADHD patients, in this
      study, investigators will investigate the effectiveness of multiple sessions of cathodal tDCS
      over the left DLPFC on inhibitory control in children and adolescents with ADHD. tDCS
      (cathodal/sham) will be applied every day for five consecutive days. Behavioral and
      neurophysiological parameters using an inhibitory task (go/no-go tasks) and the no-go N2 and
      P3 ERP components will be measured before tDCS, immediately after 5 sessions of tDCS, one
      week later, and one month after treatment onset.
    

Intervention name(s): tDCS
Intervention type(s): Device
Intervention description(s): Five sessions (active/sham) will be held on five consecutive days. The parameter of electrode size, current strength and current duration were previously tested for safety in children
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment