Strength of attention-sampling parietal EEG theta rhythm is linked to impaired inhibition in adult ADHD

Attention-deficit hyperactivity disorder (ADHD) in adults is understudied, especially regarding neural mechanisms such as oscillatory control of attention sampling. We report an EEG study of such cortical oscillations, in ADHD-diagnosed adults taking a continuous performance test that measures the ability to sustain attention and inhibit impulsivity for a prolonged period of time. We recorded 53 adults (28f, 25m, aged 18-60), and 18 matched healthy controls, using 128-channel EEG. We analysed features with established links to neural correlates of attention: event-related (de)synchronisation (ERS), alpha and theta frequency band activation, and stimulus-locking indices; in frontal and parietal scalp regions. Test performance distinguished healthy controls from ADHD adults. The ADHD group manifested significantly less parietal 4 Hz theta ERS during correct inhibition trials, in addition to having greater sensitivity to targets in stimulus-locking measures. Our results suggest that ADHD adults have impaired attention sampling in relational categorisation tasks.