Emotional arousal ripples across time to bind subsequent episodes in memory

Time unfolds continuously, yet our memories are stored as discrete episodes. Prior work shows that fluctuations between stability and change in an ongoing neutral context facilitates this formation of distinct and memorable events. However, less is known about how shifting emotional states influence these memory processes, despite ample evidence that emotion has a robust influence on non-temporal aspects of episodic memory. Here, we examined if emotional stimuli influence temporal memory for recent event sequences. Participants encoded lists of neutral object images while listening to pure auditory tones. At regular intervals within each list, participants heard emotional positive, negative, or neutral sounds, which served as ‘emotional event boundaries’ that divided each sequence into discrete auditory events. Temporal order memory was tested for neutral item pairs that either spanned an emotional sound (‘boundary-spanning’) or encountered within the same auditory event (‘same-context’). We found that highly arousing boundaries had opposite effects on binding ongoing versus subsequent sequential representations in memory. Specifically, highly arousing emotional sounds tended to lead to worse temporal order memory for boundary-spanning item pairs. By contrast, they led to better temporal order memory for same-context item pairs in the next event. Both of these arousal effects were specific to negative sounds. The carryover effect of negative arousal was also strongest for item pairs encountered closest to the boundary and diminished as the event unfolded. These findings suggest that temporally dynamic emotional states support the temporal integration of mnemonic events, which may contribute to the hyper-episodic nature of negative emotional memories.