How the brain segments experience: ERP evidence of event boundaries enhancing memory formation in narratives

Event boundaries are known to have an impact on how discrete events are remembered; however, the neural mechanisms supporting memory for boundaries themselves remain poorly understood. This study investigated how both event boundaries and preceding information are processed and remembered while listening to naturalistically spoken narratives. We recorded participants' neural responses (event-related potentials) while they listened to stories where a critical word signaled either a predictable (no-event boundary) or an unpredictable (event boundary) action. Critical words in the boundary condition were better remembered than those in the no-event boundary condition and elicited a larger N400 amplitude. Crucially, a subsequent memory effect was observed only in the boundary condition, with remembered critical words eliciting more negative N400s than forgotten ones, highlighting the role of increased demands in conceptual semantic processing in episodic memory encoding. Furthermore, a retrograde subsequent memory effect emerged also exclusively in the boundary condition, with more negative amplitudes to critical words when preceding information was later remembered, consistent with the notion that boundaries trigger rapid reinstatement of a recently experienced event. These findings provide compelling evidence that event boundaries act as "cognitive anchor points" that enhance the encoding of new information and also contribute to the strengthening of recently encoded events.