Adult ADHD Treatment Based on Combination of Dialectical Behavior Therapy (DBT) and Transcranial Direct Current Stimulation (tDCS) as Measured by Subjective and Objective Scales

The Effects of tDCS on Adult ADHD

tDCS is considered to be a non-invasive brain modulation method that is centered on cortical excitability by applying a weak current through the scalp. The modulation of cortical excitability depends on the polarity (anodal or cathodal stimulation) of electrodes. It is suggested that, in general, the anodal stimulation increases excitability of neural populations while the cathodal stimulation decreases it (Nitsche & Paulus, 2000). This intervention method has been successful in improving behavioral inhibition (Beeli et al., 2008; Mayer et al., 2020), and attentional processing (Westwood et al., 2021). Previous research (Jacobson et al., 2011) reported that unilateral anodal stimulation with tDCS over the right inferior gyrus enhanced inhibitory processes as assessed by a stop signal task (Verbruggen et al., 2008). Prehn-kristensen et al. (2014) demonstrated that tDCS improves declarative memory performance as well as enhanced reaction times in a go/no go task in individuals with ADHD (Prehn-Kristensen et al., 2014). The enhancement of inhibitory control and attention with tDCS has been investigated and the results indicated anodal stimulation improves these measures. Further work, indicated that resting state EEG showed decreased Theta (3–7 Hz) activity compared to sham stimulation, reflecting improved attention (Jacobson et al., 2012). Functional imaging and EEG studies report a network consisting of cortical areas and subcortical regions that are related to ADHD populations. As an example, Li et al. (2006), showed that efficient response inhibition was linked with increased cortical activity in frontal areas (Li et al., 2006). In short, in many studies it is reported that the dorso-lateral prefrontal cortex (DLPFC) is involved in behavioral control and attentional processes and dysregulation of these cortical areas contribute to ADHD symptoms observed in children and adults.

DBT and Adult ADHD

Given the fact that prior works support a neurophysiological bases for ADHD, several research point to the conceptual aspects of the disorder. In line with recent theories concerning ADHD, the neurophysiological impairments produce disruptions in higher order levels of cognitive processing including organization and planning strategies. The interaction of these two underlying problems led researchers to also focus on compensatory behavioral strategies in order to treat adult ADHD (Ramsay & Rostain, 2014). The preliminary psychotherapy reports in adults with ADHD were centered on insight-oriented psychotherapy (Ratey et al., 1992). However, these methods were unsuccessful and suggested the need for structured interventions. DBT was initially used for treatment of chronic suicidal behaviors and borderline personality disorder (BPD). It has been reported to be effected in a broader range of disorders that are associated with emotional and behavioral dysregulations (Koerner & Dimeff, 2007). Since BDP and ADHD share several behavioral aspects including impulsivity and emotion dysregulation, DBT, which is a cognitive-behavioral approach, was thus adapted for the treatment of adult ADHD (Hesslinger et al., 2002; Philipsen et al., 2007). Based on the analysis of pre and post-tests, participants in DBT group compared to the control demonstrated improvements on self-scale reports and a check-list of ADHD symptoms (Hesslinger et al., 2002). The following work that was conducted with a larger sample (N = 66), also indicated significant decrease in self-report scales of ADHD symptoms and other related measures (Philipsen et al., 2007). Since then several authors reported the effectiveness of DBT for adults with ADHD (Bayat et al., 2019; Hirvikoski et al., 2011; Morgensterns et al., 2016; Narimani et al., 2014; Philipsen et al., 2010). Overall, given the effectiveness of DBT, skill training might be an appropriate intervention for treatment of ADHD.

Current Work

A promising avenue for stepping up treatment is the combination of tDCS with psychotherapy methods. The combination of these methods is encouraging from both practical and mechanical perspectives. From a practical point of view, the combination of tDCS and cognitive-behavioral therapy methods such as DBT is feasible and safe. From a mechanistic point of view, we might obtain additive effects of both methods in terms of bottom-up and top down modulations. That is to say, when a specific neural network (bottom-up modulation) that is related to psychological aspects of interest (top down) is modulated, the combination of methods may lead to synergic effects (Spagnolo et al., 2020). As far as we know, only one research was focused on the efficacy of concurrently combining tDCS with a neurobehavioral method. The authors of this work report that application of left DLPFC tDCS in conjunction with cognitive training showed decreased impulsivity rates (Allenby et al., 2018). Due to a paucity of data in this line of research, we aimed to investigate the clinical outcomes of treating adult ADHD by combining two interventions of tDCS and DBT. We also explored whether the administration of combined methods might lead to optimized results when compared with conduction of each method separately. Therefore, the main research question was whether tDCS as an add-on therapy to DBT in adults with ADHD could produce greater significant improvements as measured by several scales, when compared to DBT and tDCS alone.

Participants

The study population included 580 patients who referred to the Psychotherapy and Counseling Center of Shiraz University in 2020. A total of 120 patients were given a written explanation of the study and were suggested to participate in the project. After conducting a structured clinical interview (based on DSM-V) under the supervision of a psychiatrist and psychologist and having inclusion criteria, a total of 80 adults with ADHD (63 females, 17 males) aged between 18 to 45 (mean age = 23.5; SD = 2.9) participated in the study. The inclusion criteria were receiving a diagnosis of ADHD and the ability to collaborate on the research project. Based on the structured clinical interview (DSM-V), potential participants meeting any of the following criteria were excluded from the study: any contraindication to receive tDCS, any comorbid neurologic or psychiatric disorder (such as comorbid depression, anxiety etc.) other than ADHD, history of substance abuse within the past 6-months and receiving other psychological and medication-based treatments at the same time. A simple randomization method based on a single sequence of random assignments was used. For this purpose, a computer-generated table containing random numbers was employed. The participants were then randomly assigned into four groups, each containing 20 participants (three experimental groups and one control group). The control group did not receive any treatments. The three experimental groups consisted of DBT, tDCS, and combined treatment groups. Because of the local ethical considerations, it was not possible for us to have a sham tDCS group. All participants provided informed consent. All of the procedures of the study were approved by the Local Committee and carried out in accordance with the Declaration of Helsinki.

Materials

The following psychometric scales were used to measure changes in terms of clinical improvement:

Treatments

DBT protocol

Individual DBT sessions (N = 10) were carried out at the start of tDCS administration and lasted 10 weeks. The sessions were conducted once a week, for 1 to 1.5 hours. Weekly psychotherapy sessions began with exploring an event or problematic behavior and reviewing the suggested solutions that have been used and the factors that the clients seek. The complete protocol of DBS sessions that were conducted for the DBS and combined groups are presented in Table 1.

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Table 1.

The Protocol of DBT Carried Out for DBT and Combined Groups.

Sessions	Subjects
1	Clarification and introduction
2	Teaching the basic skills of tolerating turbulence
3	Advanced turbulence skills: Using the present moment
4	Basic skills of mindfulness
5	Advanced skills of mindfulness
6	Explore more about mindfulness
7	Basic emotional regulation skills
8	Effective communication skills
9	Advanced effective communication skills
10	Conclusion

Procedure

An ethical code from the Local Authorities was obtained (registered at ethics.research.ac.ir with No. IR.SUMS.REC.1398.781). Then, structured interviews according to DSM-5 were used to screen a sample of the statistical population. The sample was then grouped into the aforementioned groups. After assignment in the groups, the stage of pre-tests was performed and all participants completed the measures introduced in the Materials section. Then, each experimental group (tDCS alone, DBT alone and combination of the two) received the related treatment protocol. After the intervention, post-tests were carried out for all four groups (Figure 1).

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Figure 1.

Overview of the study design.

DBT and Adult ADHD

The results showed that DBT is effective in improving most of the symptoms of adults with ADHD, as reflected in amelioration of problems in selective attention and response inhibition (ST), sustained attention (CPT) and emotion regulation (DERS). However, DBT group did not reflect improvement in ASRS in terms of subjective attention. Indeed, based on ASRS results, the participants experienced a significant improvement in hyperactivity due to DBT intervention, but no improvement was observed in the attention subscale. These findings might be explained by the fact that mindfulness training in DBT increases effective self-regulation and cognitive controls. In addition, as reported elsewhere (Bueno et al., 2015) mindfulness in DBT might establish a stable pattern of deactivation in brain regions that are related to motor activities. In terms of attentional processing, the lack of DBT effect in ASRS might be explained by the fact that the sample studied in this research included more female than male participants. In previous studies (Weiss et al., 2003), it has been shown that female patients are more likely to be hyperactive than male patients. To explain this finding, we must also consider that the ASRS is a self-reported inventory that assesses a person’s mental assessment of attention. Given that computer programs measure a person’s level of attention in the context of the procedure, but the ASRS is only a report of the patient’s assessment of performance, the differences might be explained by the fact that different scales might lead to different results in terms of subjective and objective factors (Söderström et al., 2014). Regarding emotion regulation (DERS), previous works have shown that mindfulness techniques in DBT enhances the abilities related to increased awareness of one owns feelings (Zalewski et al., 2018). Indeed, effective relationship skills can be considered as a mediating component to keep adults with ADHD away from emotional turmoil (Groß et al., 2019). In other words, one might conclude that due to the mechanisms underlying DBT such as acceptance, mindfulness, in combination with cognitive-behavioral therapy techniques, the treatment’s effectiveness in empowering patients to regulate their emotions.

tDCS and Adult ADHD

The results of the present study showed that tDCS had significant effects on most symptoms of ADHD in adults. Indeed, the tDCS group alone indicated enhanced selective attention and response inhibition (ST), sustained attention (CPT), and emotion regulation (DERS). Regarding attention, the present work was focused on two types of attentional processing: selective and sustained attention as measured by ST and CPT, respectively. According to the previous findings, DLPFC is involved in both types of attention. (Dubreuil-Vall et al., 2019; Salehinejad et al., 2020). tDCS has been utilized for a variety of cognitive functions (Ghanavati et al., 2019) and in line with our results its effects on attention has been approved (Oberman & Enticott, 2018). These results are consistent with reports that suggested the beneficial effects of tDCS for ADHD. Indeed, a recent meta-analysis of the research that used tDCS indicated that stimulation of the DLPFC is effective on different attentional tasks (Yadollahpour et al., 2017).

However, the participants in the tDCS only group did not reveal any significant improvement on hyperactivity scale as measured by subjective scale of ASRS. One explanation might point to the fact that hyperactivity scales are more related to the sensory-motor areas of the brain that were not modulated during our tDCS sessions. Another possible explanation for the lack of tDCS effects for hyperactivity scale and significant results for attentional processing might be related to learning effects in attention scores at pre-test phase. On the other hand, differences in stimulation and treatment paradigms such as stimulation amplitude and/or presentation of stimuli might explain the null results.

Furthermore, the results of post-test of the DERS indicated that our tDCS protocol led to improved emotion regulation in tDCS alone group. This result validate the previous findings, that is, the DLPFC is a core area of emotional regulation (Basiri et al., 2021; He et al., 2018). Brain imaging research also shows that participants had significant activation in DLPFC and dorsal anterior cingulate cortex (dACC) in the social context with emotional aspects (Eisenberger et al., 2003). It is speculated that left frontal anodal stimulation led to enhancement of regulation of the dACC in this brain regions, so that participants obtained improved scores in DERS. The contribution of our findings is that they might extend the proposed tDCS protocol to be used in adults with ADHD.

tDCS Combined With DBT for Adult ADHD

Research in the field of combining tDCS with psychological interventions is flourishing. Despite the fact that tDCS alone did not significantly improved hyperactivity scale and DBS alone did not influence inattention scale, the most promising results (as measured by both subjective and objective scales) were observed when tDCS was concurrently combined with DBT. Our findings revealed improvement after combined method in all subjective and objective measures (ASRS, ST, CPT and DERS). As discussed in the previous section regarding to the tDCS alone, this modulation improved inattention scale in ASRS. However, such result was not observed for DBT alone. The significant findings for the combined synergic effect for inattention scale, might be related to the additional effects of tDCS on DLPFC cognitive functions. The mentioned effects was thus augmented due to mindfulness training carried out in DBT sessions. Interestingly, the adults with ADHD that have problems in DLPFC functioning might not have benefited from DBT, therefore, tDCS administration increased the effectiveness of this psychological intervention. As discussed the hyperactivity scale in ASRS was not improved in tDCS group, but DBT group revealed improvements in this scale. The combined method, however, showed improvement in this scale indicating the efficacy of DBT.

Similar findings were reported previously regarding major depression and anxiety (Nasiri et al., 2020) and post-traumatic stress disorders (Philip et al., 2019). Such results are indeed interpretable both from a neuropsychological and neurophysiological perspectives. Of note, it is not clear whether significant results in all subjective and objective measures in combined group were due to the specific influence of tDCS on the neurophysiological mechanism of action that was involved in DBT.

Concluding Remarks

Optimization of the clinical effects of DBT combined with tDCS, represents a potential avenue to focus on brain plasticity and enhance the therapeutic effects. However, we believe that using psychotherapy methods in conjunction with neurotherapy requires understanding mechanistic and psychologic aspects that might influence the potential synergic effects for ADHD. Of importance, the available data, including ours, suggests that concurrent treatments can be preferred as opposed to separate or sequential administration of the methods. As an example, it is reported that applying one-session tDCS concurrently with a cognitive or behavioral task leads to greeter improvement as compared with sequential administration (Besson et al., 2019). Furthermore, in a meta-analysis performed on DLPFC single-sessions of tDCS combined with tasks indicated enhanced effects on cognition as compared with sequential method (Dedoncker et al., 2016). We shall hereby propose that synergic effects of psychotherapy methods such as DBT and tDCS is greater as the ADHD patients taught several new skills to regulate cognition, emotion, and behavior. We suggest combined methods may provide improved brain functioning in addition to opportunity to teach the ADHD adult how to use the neural enhancement to advantage more from the DBT (De Raedt et al., 2015). To summarize, our findings showed that merely applying tDCS or DBT alone might not improve cognitive and behavioral functioning. tDCS, thus, might act as a “restoration” tool to benefit from DBT intervention. Set against the strengths of our research we shall hereby point to several limitations. Major limitations of this research were lack of the sham tDCS group and the fact that assessments were not blinded. As mentioned before, we were not allowed to include such control group due to our Local Committee’s considerations. Clearly, further comparisons with sham-controlled groups and blinded assessment are required for the robust demonstration of the efficacy of any protocol with tDCS. Second, we did not conducted any follow-up for several months due to lack of access to all participants. Third, most of the participants in the study were females and due to the different aspects of cognition and symptoms of ADHD, the generalization of results might be limited. Fourth, optimal tDCS stimulation might be carried out considering the brain map of each individual and due to the related costs and unavailability of facilities, we have used the common protocol of stimulation. On the other hand, as various cognitive problems require different targets, other neural targets might have to be explored in future works. In the same vein, future works might determine the optimal duration of combined interventions. This issue is not an easy procedure because the parameters of stimulation and psychotherapy are different across different disorders.