Constricted pupil states index neural replay during wakeful rest in humans

Neural replay has been linked to skill consolidation during wakeful rest, yet its physiological context in humans remains poorly understood. In animals, hippocampal ripples and associated replay occur more frequently within intrinsically oriented brain states associated with constricted pupils, suggesting that pupil dynamics may index neural replay events in humans. We combined magnetoencephalography-derived sequence replay with pupillometry in 25 participants learning a motor sequence across alternating intervals of practice and rest. Replay was indexed by smaller-pupil states, and replay timing clustered on the constricting phase of slow pupil fluctuations. More frequent replay accompanied larger cumulative offline gains during early learning, while smaller rest pupil was associated with better performance when practice resumed. Multivariate pupil features predicted replay-associated states across and within individuals while preceding pupil dynamics showed modest predictive ability to identify the precise onset of individual replay events. Here, we show that constricted-pupil states index neural replay during wakeful rest in humans, linking replay-associated physiology with early motor learning.