Low frequency oscillations of response time explain parent ratings of inattention and hyperactivity/impulsivity

Greater intra-subject variability (ISV) in response time is a heritable endophenotype of attention-deficit/hyperactivity disorder
(ADHD). Spontaneous low frequency oscillations (LFO: 0.01–0.1 Hz) observed in brain functional magnetic resonance signals
might account for such behavioral variability. Recently, we demonstrated that ISV in response time (RT) explained ratings
of ADHD symptoms. Building on this finding, here we hypothesized that LFO in RT time series would explain these ratings, both
independently and in addition to RT coefficient of variation (CV). To measure RT LFO, we applied Morlet wavelet transform
to the previously collected RT data. Our community sample consisted of 98 children (including 66 boys, mean age 9.9 ± 1.4 years),
who completed four computer Tasks of Executive Control. Conners’ Parent Rating Scale ratings were obtained. RT LFO of three
tasks significantly explained ratings of inattention, hyperactivity and three global Conners’ subscales. In addition, RT LFO
during two tasks that included an inhibitory component increased the proportions of variance explained in subscales of both
inattention and hyperactivity/impulsivity, beyond the effects of RT-CV. Three specific low frequency bands (Slow-5: 0.01–0.027 Hz;
Slow-4: 0.027–0.073 Hz; Slow-3: 0.073–0.20 Hz) were strongly related to the ADHD scales. We conclude that RT LFO predict dimensional
ratings of ADHD symptoms both independently and in addition to RTCV. Results suggest that frequency analyses are a suitable
methodology to link behavioral responses to putative underlying physiological processes.