Hippocampal immediate poststimulus activity in the encoding of consecutive naturalistic episodes.

Abstract

In the encoding of narrative episodes, the hippocampus exhibits memory-predictive activity time-locked to stimulus offset. In real life, however, events usually occur in succession, raising the question of how the immediate offline processing of one event is affected by presentation of another. To address this issue, participants were presented with brief narrative movie clips in a functional magnetic resonance imaging scanner. Each clip was immediately followed by an additional, unrelated, clip; by a visually scrambled clip with background auditory noises; or by a fixation cross. Memory for the gist of the clips was tested outside the scanner in a cued-recall test 20 min after termination of the study session. The hippocampus responded at the offset of each clip, even when a second clip was presented in immediate succession, suggesting that the hippocampus processes each brief clip as a discrete event. Presentation of a second narrative clip, and to a lesser degree of a scrambled clip, retroactively interfered with memory for the first clip. In parallel, the offline response of the posterior hippocampus to the first movie was reduced. In the anterior hippocampus, presentation of a second clip did not reduce the overall offline response but significantly reduced the difference in activity between remembered and forgotten clips. These findings are in line with the proposition that immediate offline hippocampal activity reflects registration of episodes to memory and suggest a potential brain correlate of retroactive interference.

The Consolidation and Transformation of Memory

“…When in their paradigm a clip event was immediately followed by an interfering stimulus, the offset response to the first clip was attenuated in a manner corresponding to the behavioral interference (Ben-Yakov et al, 2013). This is in line with the suggestion that the hippocampal offset-locked response constitutes a signature of, an early step in, the initiation of a consolidation process.…”

“…Nonetheless, even in the absence of human cellular data, the available fMRI results suggest that the offset-locked hippocampal response may underlie episodic binding, potentially triggered by the occurrence of an event boundary (Kurby and Zacks, 2008). Ben-Yakov et al (2013) demonstrated that presentation of two distinct episodes in immediate succession elicited two distinct hippocampal responses, at the offset of each episode, consonant with the idea that the hippocampal response is shaped by the content of the stimulus and triggered by event boundaries.…”

“…However, insight into potential processes and mechanisms of the initiation of consolidation at the systems level is fragmentary. In a recent set of studies, Ben-Yakov and Dudai (2011) and Ben-Yakov et al (2013 examined the first seconds following the inception of an episodic memory. They combined a protocol of ''subsequent memory'' with brief movie clips memoranda intercalated with brief rest periods.…”

Dynamic changes in prefrontal cortex involvement during verbal episodic memory formation

“…There are only a handful of fMRI studies that selectively focused on post-stimulus brain activity (Ben-Yakov & Dudai, 2011;Ben-Yakov, Eshel & Dudai, 2013;Elman, Rosner, Cohn-Sheehy, Cerreta & Shimamura, 2013). These studies have not only shown that this activity is crucial for memory formation, but also that brain activations after the offset of a stimulus are dissociable from those related to earlier, on-line processing.…”

Does a turn in the road mark a turn of events? Turns along travelled routes provide contextual boundaries during navigation

“…The inflation of pre-boundary temporal information and increased subjective recollection may be produced by a post-boundary peak in hippocampal activity, which enables binding of preboundary information into a cohesive event (Baldassano et al, 2017;Ben-Yakov & Dudai, 2011;Ben-Yakov, Eshel, & Dudai, 2013). This retroactive signal might therefore result in an enrichment of pre-boundary, relative to post-boundary information.…”