Diminished modulation of preparatory sensorimotor mu rhythm predicts attention-deficit/hyperactivity disorder severity.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) is characterized by problems in regulating attention and in suppressing disruptive motor activity, i.e. hyperactivity and impulsivity. We recently found evidence that aberrant distribution of posterior α band oscillations (8-12 Hz) is associated with attentional problems in ADHD. The sensorimotor cortex also produces strong 8-12 Hz band oscillations, namely the µ rhythm, and is thought to have a similar inhibitory function. Here, we now investigate whether problems in distributing α band oscillations in ADHD generalize to the µ rhythm in the sensorimotor domain. METHOD: In a group of adult ADHD (n = 17) and healthy control subjects (n = 18; aged 21-40 years) oscillatory brain activity was recorded using magnetoencephalography during a visuo-spatial attention task. Subjects had to anticipate a target with unpredictable timing and respond by pressing a button. RESULTS: Preparing a motor response, the ADHD group failed to increase hemispheric µ lateralization with relatively higher µ power in sensorimotor regions not engaged in the task, as the controls did (F 1,33 = 8.70, p = 0.006). Moreover, the ADHD group pre-response µ lateralization not only correlated positively with accuracy (r s = 0.64, p = 0.0052) and negatively with intra-individual reaction time variability (r s = -0.52, p = 0.033), but it also correlated negatively with the score on an ADHD rating scale (r s = -0.53, p = 0.028). CONCLUSIONS: We suggest that ADHD is associated with an inability to sufficiently inhibit task-irrelevant sensorimotor areas by means of modulating µ oscillatory activity. This could explain disruptive motor activity in ADHD. These results provide further evidence that impaired modulation of α band oscillations is involved in the pathogenesis of ADHD.

Cognitive flexibility depends on white matter microstructure of the basal ganglia.

Ample evidence shows that the basal ganglia play an important role in cognitive flexibility. However, traditionally, cognitive processes have most commonly been associated with the prefrontal cortex. Indeed, current theoretical models of basal ganglia function suggest the basal ganglia interact with the prefrontal cortex and thalamus, via anatomical fronto-striato-thalamic circuits, to implement cognitive flexibility. Here we aimed to assess this hypothesis in humans by associating individual differences in cognitive flexibility with white matter microstructure of the basal ganglia. To this end we employed an attention switching paradigm in adults with ADHD and controls, leading to a broad range in task performance. Attention switching performance could be predicted based on individual differences in white matter microstructure in/around the basal ganglia. Crucially, local white matter showing this association projected to regions in the prefrontal cortex and thalamus. Our findings highlight the crucial role of the basal ganglia and the fronto-striato-thalamic circuit for cognitive flexibility.