Abstract
The purpose of this study was to investigate sustained attention through modulation of the fronto-cerebral network with transcranial direct current stimulation (tDCS) in adults with attention-deficit/hyperactivity disorder (ADHD) and control participants. Thirty-seven participants (21 with ADHD) underwent three separate sessions (baseline, active tDCS, and sham) and performed the MOXO Continuous Performance Test (CPT). We applied double anodal stimulation of 1.8 mA tDCS for 20 min over the left and right dorsolateral prefrontal cortex (DLPFC), with the cathode over the cerebellum. Baseline session revealed significant differences between ADHD and control participants in the MOXO-CPT attention and hyperactivity scores, validating the MOXO as a diagnostic tool. However, there were no tDCS effects in most MOXO-CPT measures, except hyperactivity, due to a significant learning effect. We conclude that learning and repetition effects in cognitive tasks need to be considered when designing within-subjects tDCS experiments, as there are natural improvements between sessions that conceal potential stimulation effects.
Highlights
Attention-deficit/hyperactivity disorder (ADHD) is a neuropsychiatric disorder which is typified by developmentally inappropriate symptoms of inattention, impulsivity, and hyperactivity, that are present in various surroundings, leading to deficits in social, educational or work settings, and impacts different domains of cognitive skills such as executive functions (EF) and cognitive control (Lijffijt et al, 2005; Barkley, 2010; American Psychiatric Association [APA], 2013)
EF is an umbrella term comprising a wide range of complex cognitive processes that enable goal-directed behavior, such as planning and executing tasks while staying concentrate and transcranial direct current stimulation (tDCS) Effects on Sustained Attention focused, dysfunction in such processes has been long recognized as the hallmark of ADHD (Barkley, 1997, 2012; Castellanos et al, 2006)
There were no significant differences between the groups (ADHD/control) in all the demographic measures
Summary
Attention-deficit/hyperactivity disorder (ADHD) is a neuropsychiatric disorder which is typified by developmentally inappropriate symptoms of inattention, impulsivity, and hyperactivity, that are present in various surroundings (e.g., school and home), leading to deficits in social, educational or work settings, and impacts different domains of cognitive skills such as executive functions (EF) and cognitive control (Lijffijt et al, 2005; Barkley, 2010; American Psychiatric Association [APA], 2013). Attention-deficit/hyperactivity disorder arises from disorders in the prefrontal cortex (PFC) which is the main region regulating EF and self-monitoring (Barkley, 1997; Brown, 2013). In a functional magnetic resonance imaging (fMRI) study, Schneider et al (2010) compared adults with ADHD and control participants while they performed continuous performance test (CPT), their findings demonstrated impaired activation of the PFC, cerebellum, cingulate cortex (ACC), the fronto-striatal and parietal attentional network in ADHD subjects
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