Response variability in ADHD: exploring the possible role of spontaneous brain activity

Attention-Deficit/Hyperactivity Disorder (ADHD) is the most common psychiatric disorder of childhood and manifests as symptoms of developmentally inappropriate inattention, impulsivity and hyperactivity. Although numerous deficits have been identified in ADHD, one of the most consistent findings is that patients with ADHD are more variable in the speed of their reaction time (RT) responses on neuropsychological tasks than control children. In 2008, the default-mode interference hypothesis of ADHD was introduced by Sonuga-Barke and \nCastellanos as a biologically plausible account of this increased within-subject variability in ADHD. This hypothesis suggests that some patients with ADHD might not effectively attenuate low frequency resting brain activity from rest to task and that these low frequency oscillations may then intrude onto task performance and cause periodic attention lapses. These periodic attention lapses would manifest as increased variability in RT data. \n \nThe present thesis provided the first test of this hypothesis using DC-EEG. We assessed the power in very low frequency EEG bands (< .1 Hz) during rest and during goal-directed task performance in two samples. First was a sample of adults who self-reported either high- or low-ADHD scores, and second was a clinic referred sample of adolescent boys with ADHD and age- and gender-matched controls. We found that in both samples, low frequency EEG was generally attenuated from rest to task, but the degree of this attenuation was lower in ADHD or inattentive participants compared to controls. We also found that periodicity was evident in RT data, and that there was synchrony between low frequency fluctuations in RT data and low frequency EEG. These findings provide some initial support for the default mode interference hypothesis. The findings also highlight the potential involvement of low frequency electrodynamics in attentional processes and in the pathophysiology of ADHD.