Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HippBoundariesPE (Identifying the building blocks of episodic memory: how the hippocampus parses boundless experience into discrete events)

Teaser

As we go about our lives, we experience a continuous stream of information. Yet when thinking about the past, we remember it as discrete events – ‘I attended a meeting’; ‘I went to see a movie’. How is our continuous experience transformed into these separate...

Summary

As we go about our lives, we experience a continuous stream of information. Yet when thinking about the past, we remember it as discrete events – ‘I attended a meeting’; ‘I went to see a movie’. How is our continuous experience transformed into these separate memories? Research has shown that people naturally segment experience into events, with relatively high agreement between them as to when transitions between events (event boundaries) occur. The current project is aimed at revealing how event boundaries affect the memory systems in our brain in charge of encoding new memories. An intriguing hypothesis, which we set out to test, is that event boundaries trigger activity in brain regions in charge of memory encoding. We found that event boundaries indeed trigger a strong response in the hippocampus, a key region involved in encoding of new episodes, and that the response was stronger for more salient boundaries. Moreover, the hippocampus responded primarily during these boundaries, and relatively little at other points in time. Together, this suggests that during continuous experience, event boundaries may trigger encoding activity that wraps up the preceding event as a cohesive unit, separating it from the next event. This project is part of a global objective to understand how we form memories for entire events. Memory research has traditionally focused on how the brain encodes memories for simple items, such as words, or pictures. By expanding our knowledge to uncover how the brain encodes whole episodes, which are much more similar to our real-life experience, we are laying the foundations for a better understanding of memory disorders.

Work performed

One of the main methods of studying human brain function is functional magnetic resonance imaging (fMRI). This enables researchers to measure brain activity while people are performing various tasks, such as learning new information. We analysed data from people who watched films in fMRI scanners – 253 people who watched an 8-min Hitchcock film (www.cam-can.org) and 15 people who watched Forrest Gump (www.studyforrest.org). A different set of people watched the two films on a computer and indicated when they felt there was a shift from one event to another. We found that the hippocampus – a region strongly identified with encoding of new memories – is particularly active at an event boundary. And more salient boundaries (identified by more people), elicited more activity in the hippocampus. This suggests that event boundaries may shape our memories by triggering the hippocampus to encode the preceding event to memory, “saving” it as a separate unit, and clearing the slate for the next event. The results from this study were published in the Journal of Neuroscience and have been presented at public engagement events such as Pint of Science.

Final results

While memory encoding has been the focus of a wealth of laboratory research, a critical gap remains – we know surprisingly little regarding real-life memories, which are by far more complex than the type of items typically used to study memory. In this project, we transition to the study of more naturalistic experience, examining the brain response in memory-encoding regions while watching a continuous film. It is part of a wider goal, to identify the basic unit of episodic memory, answering the question – what is an episode? Revealing how our brains encode entire events to memory lays the foundations for a better understanding not only of the mechanisms of intact human memory, but also memory disorders, a prevalent concern in today’s society.

Website & more info

More info: https://www.mrc-cbu.cam.ac.uk/people/aya.ben-yakov/.