Chronotype and Time of Day Effects in Oddball Task Performance: Behavioural and Cerebral Correlates

Circadian rhythms and inter-individual differences in sleep-wake preferences, or chronotypes, influence cognitive performance. The synchrony effect-the alignment of time of day with chronotype-modulates attention, memory, and executive control. This study examined behavioural and neural correlates of synchrony effects during an auditory oddball task performed in morning (1.5 h after wake-up) and evening (10.5 h after wake-up) sessions by extreme morning-type (n = 16) and evening-type (n = 15) young (age range: 22-32 y.o.) individuals. Behaviourally, no main, nor interaction effects of chronotype or time of day were observed for overall reaction time metrics (all p > 0.05). However, overall reaction times during the task were longer in the final third of the task in the evening compared to the morning session for morning but not evening types (p < 0.05). Functional magnetic resonance imaging (fMRI) revealed neural correlates underlying the synchrony effect: the inferior frontal cortex (IFC) showed higher task-related activation at optimal times (morning for morning types, evening for evening types, p_corr < 0.05), putatively reflecting enhanced top-down control. Conversely, a medial orbitofrontal region (mOFC), part of the default mode network, was more active at non-optimal times (p_corr < 0.05), consistent with reduced task engagement and internally directed processes. These findings suggest that synchrony effects interact with time-on-task-dependent effects with implications for sustained attention in real-world settings.