Time-resolved aperiodic dynamics in event segmentation in attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is associated with difficulties in organizing behaviour over time, yet the neurophysiological mechanisms underlying these temporal control deficits remain poorly understood. The brain continuously segments ongoing experience into discrete events to guide prediction and adaptive action. In our study, we examined whether adolescents with ADHD differ from neurotypical (NT) peers in how they behaviourally and neurally structure continuous experience. Seventy-three adolescents with ADHD and 73 adolescent NT controls viewed a movie while indicating perceived event boundaries. Concurrent EEG recordings were analysed using time-resolved spectral parameterization to track moment-to-moment changes in aperiodic neural activity. Both groups detected meaningful transitions, but NT adolescents segmented more sensitively to situational changes, particularly social and spatial cues. Across the entire recording window, ADHD participants exhibited steeper aperiodic exponents than NT participants across boundary and no-boundary intervals. Time-resolved analyses revealed that, around event boundaries, ADHD participants showed exaggerated pre-boundary steepening and attenuated post-boundary flattening of the aperiodic exponent-signifying over-stabilization before, and insufficient re-engagement after, event transitions. In ADHD only, behavioural segmentation sensitivity correlated with post-boundary aperiodic modulation. Although counterintuitive given common assumptions about increased neural 'noise' in ADHD, this pattern indicates that ADHD is characterized by an imbalance between neural stabilization and re-engagement when parsing continuous experience. Steeper aperiodic activity reflects a restricted neural state space that limits adaptive updating, leading to less context-sensitive segmentation. These findings link everyday temporal disorganization in ADHD to alterations in aperiodic neural dynamics and impaired temporal cognition in ADHD.