Attention Deficit / Hyperactivity Disorder (ADHD) is a psychological disorder that begins in childhood and results in disproportionate levels of development in the areas of inattention, impulsivity, and hyperactivity; The prevalence of this disorder in children is 3.53%; In many cases, it has been shown to persist into adulthood, and the prevalence of this disorder in adulthood can be 3.4% (1). This disorder becomes one of the most pervasive developmental neurologic disorders of childhood which showed that it is too current, inattentive or both (2) and with more deficits in cognitive dimensions such as attention and inhibitory control (3). Other cognitive deficits in this dosorde include attention problems, motivational control, and timing (4), indicating that the disorder is in the context of executive functions (5).
Despite the apparent heterogeneity in the neuropsychological formation of Attention Deficit/Hyperactivity Disorder(6), two main models have been hypothesized to explain the behavioral deficits: one, the "model based on inhibition or cognitive impairment." Suggests that inhibition-based executive defects are major defects in the disorder, and lead to failures in executive control that actually lead to impulsive and hyperactive behavior. The "motivational distortion model" emphasizes defective reward processing instead of cognitive deficits, suggesting that behavioral deficits in Attention Deficit /Hyperactivity Disorder result in decreased arousal (7). In other words, poor executive resources (inhibition-based model) and impulse control deficiencies that lead to hyperactivity (motivational dysfunction model) are effective theories in physiological pathology of attention deficit hyperactivity disorder. According to the first model, the decision-making factor leads to incomplete executive functions with hypo-function of the dorso-lateral pre-frontal cortex (DLPFC) as well as hyperactivity of the subcortical areas Some executive reactions may play a more fundamental role in the symptoms and defects of this disorder, such as cognitive flexibility, inhibitory control, and selective attention (8).
1.1 mindfulness-based cognitive therapy and ADHD
In the treatment of this disorder, drug administration has increased dramatically in recent years. But today, due to the side effects of drugs, the need to continuous use in order to maintain the effects and poor adherence to treatment, non-drug therapies have become very popular. One of the non-pharmacological therapies is mindfulness-based cognitive therapy (MBCT). This therapeutic approach is based on the stress reduction model based on the mindfulness of Kabat-Zin and by adding the principles of cognitive therapy to it. This treatment is a combination of cognitive-behavioral therapy and mindfulness and is a method of teaching sustainable attention. Mindfulness-based cognitive therapy includes attention regulation, emotional regulation, and physical awareness. A research (9) shows that mindfulness has a positive effect on behavioral inhibition. At first glance, mindfulness and ADHD seem to be a contradictory combination; but considering the key aspects of mindfulness makes it clear how useful this method is for improving the symptoms of the disorder. Mindfulness helps the person by informing of what is distracting him or her and helping to restore attention to what was previously focused on, and it can be said that it is in fact a kind of exercise of attention and excitement. Studies also show changes in the brain during mindfulness training that these changes lead to a tendency to a non-invasive stimulation method called direct transcranial electrical stimulation (10).
1.2 Transcranial direct current stimulation and ADHD
Recent studies have highlighted the importance of non-invasive brain stimulation in modulating cortical arousal (11, 12). Studies that have examined the modulatory effects of transcranial electrical stimulation on Attention Deficit / Hyperactivity Disorder are rare. Recent studies have highlighted the importance of non-invasive brain stimulation in modulating cortical arousal (10, 11). Positive results are reported during the go / do task using cathodic stimulation of the left lateral frontal cortex (13). In a study (14) authors suggested that anodic stimulation in the lower right frontal groove improves inhibitory control. In one study(15), found that cathodic stimulation in the left lateral dorsal forehead area improved inhibitory control in the go / not go task, while anodic stimulation in the same area made it difficult. Underlying this effect may be an indirect increase in cortical activity in the right prefrontal cortex, resulting in intracellular communication that enhances inhibitory control.
Barkley has identified behavioral inhibition disorders as the central deficiency of attention deficit/ hyperactivity disorder. Researchers (16) showed that transcranial electrical stimulation improves aspects of selective attention, reducing the time required to select new information and the total number of attention errors.. A study (17) shows that the application of anodic transcranial electrical stimulation to the left DLPFC region helps to improve cognitive function including selective attention, processing speed and working memory.
Neurological studies have shown several aspects of attentional abilities, but the three major parts of attentional abilities that are somehow related to mindfulness are: sustained attention, selective attention, and attention transfer. According to a research (18), correlation coefficient of mindfulness with inhibitory control and selective attention was 0.62, with a stable focus of 0.44 and with a memory of 0.41. According to a study (19), mindfulness-based cognitive exercises, in addition to their effect on sustained attention, also improve selective attention capacity. Experimental studies (20) have shown that people who participate in mindfulness exercises have a higher score on the Stroop test (selective attention assessor). About 30% of adults with the disorder do not respond to standard medication interventions (21). At best, the mediocre effects of behavioral therapy, the high rate of drug withdrawal due to side effects, and the critical attitude of parents toward drug therapy underscore the urgent need to develop alternative therapeutic strategies (22).
1.3 The present study
The aim of the present study was to investigate the effects of transcranial electrical stimulation on the lateral dorsal forehead area- which is the most involved area in behavioral inhibition disorders / attention deficit disorder-, as well as mindfulness-based cognitive therapy on inhibitory control and Attention in 45 patients with ADHD in a randomized parallel-group design. Based on previous neuroimaging studies, that showed hypoactivation of prefrontal regions of this area for attention and inhibitory control, we hypothesized that increasing DLPFC activation with anodal tDCS would result in improved inhibition and attention in ADHD (hypothesis 1). Also, according to the literature (9)(23), we hypothesized that MBCT would lead to improved selective attention and inhibition in our experimental group (hypothesis 2).