Context-Dependent Modulation of Duration Encoding in the Supplementary Motor Area

Temporal perception adapts to the statistical structure of recent experience: the brain extracts distributional statistics from encountered durations and uses these ensemble representations to alter subsequent temporal judgments. How this contextual modulation reshapes neural processing of duration, however, remains unknown. To address this question, we used functional magnetic resonance imaging (fMRI) while twenty-four participants performed a temporal bisection task under two distributional contexts--a long-biased and a short-biased frequency distribution of presented durations. Behaviorally, context shifted the point of subjective equality while preserving temporal precision, consistent with a criterion-shift mechanism rather than a change in sensory resolution. At the neural level, the supplementary motor area (SMA) exhibited a significant context and duration interaction, with duration-dependent activity strongly modulated by the distributional environment. This modulation was region-specific: the long-biased context engaged a front-cortico-striatal pathway through the SMA, the right inferior frontal gyrus (IFG), and putamen, whereas the short-biased context instead recruited the left insula. Complementary connectivity analysis (gPPI) confirmed that the SMAs functional coupling during duration encoding also shifted between contexts, extending the dissociation from regional activation to network-level communication. Together, these results reveal that temporal context does not merely bias a fixed timing circuit but dynamically reconfigures which brain networks process duration, demonstrating that the neural architecture of time perception flexibly adapts to the prevailing statistical environment.