Signals of memory building-blocks: Pupil-linked arousal predicts event segmentation and episodic memory

<title>Abstract</title> <p>People automatically segment the continuous stream of experiences into events with discrete boundaries, and these events then serve as building blocks for later episodic memories. How the brain creates these discrete event representations remains elusive. Here we investigated the role of noradrenergic (NA) transmission, heavily linked to change-detection, in identifying event boundaries while listening to auditorily presented narratives. Specifically, we investigated how pupil dilation, an indirect physiological proxy of NA activity, tracks event boundaries while listening to short stories of everyday events. In four studies, we demonstrated that event boundaries triggered significant pupil dilation peaking 4-8 seconds after the event boundary, and the magnitude of these dilations predicted later memory for the narratives. Furthermore, we also showed that pupil dilation magnitude at each time point during the narratives scaled as a function of how frequently a set of independent raters indicated the presence of an event boundary preceding that specific story location. Thus, our results demonstrate the existence of pupil dilations triggered by event boundaries and highlight the role of NA transmission in episodic memory encoding, either by signaling unexpected changes (i.e., event-boundaries) in the flow of continuous experience or by contributing to the updating of the event-models in working memory.</p>