Coding of Event Nodes and Narrative Context in the Hippocampus

Milivojevic, Branka; Varadinov, Meryl; Grabovetsky, Alejandro Vicente; Collin, Silvy; Doeller, Christian F.

doi:10.1523/jneurosci.2889-15.2016

Cited by 69 publications

(79 citation statements)

References 66 publications

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“…It is difficult however to determine how much of the hippocampal response in these experiments relates to perceptual change at discrete points in time, rather than subjective segmentation of continuous stimulation. Milivojevic et al (2016) examined hippocampal activity in a continuous film, but focused on the representation of the events themselves, rather than sensitivity to boundaries. The only prior study, to our knowledge, that examined hippocampal activity to subjective event boundaries during continuous films is that by Baldassano et al (2017).…”

Section: Discussionmentioning

confidence: 99%

The hippocampal film-editor: sensitivity and specificity to event boundaries in continuous experience

Ben-Yakov

Henson

2018

Preprint

143

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AcknowledgementsThis work was supported by the UK Medical Research Council (SUAG/010 RG91365) and a Marie Curie Individual Fellowship (705108) awarded to ABY. The research would not have been possible without the data provided by the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) and the studyforrest project. We thank Michael Hanke for his help with the studyforrest dataset, Christopher Baldassano for support with the cortical pattern shift analysis, and Katherine Storrs for her help with the convoluted neural net analysis. We also thank Roni Tibon, Andrea Greve, Alex Kaula and Alex Quent for valuable feedback. AbstractThe function of the human hippocampus is normally investigated by experimental manipulation of discrete events. Less is unknown about what triggers hippocampal activity during more naturalistic, continuous experience. We hypothesized that the hippocampus would be sensitive to the occurrence of event boundaries, i.e. moments in time identified by observers as a transition between events. To address this, we analysed functional MRI data from two groups: one (N=253, 131 female) who viewed an 8.5min film and another (N=15, 6 female) who viewed a 120min film. We observed a strong hippocampal response at boundaries defined by independent observers, which was modulated by boundary strength (the number of observers that identified each boundary). In the longer film, there were sufficient boundaries to show that this modulation remained after covarying out a large number of perceptual factors. The hippocampus was the only brain region whose response showed a significant monotonic increase with boundary strength in both films, suggesting that modulation by boundary strength is selective to the hippocampus. This hypothesis-driven approach was complemented by a data-driven approach, in which we identified hippocampal-events as moments in time with the strongest hippocampal activity: The correspondence between these hippocampalevents and event boundaries was highly-significant, revealing that the hippocampal response is not only sensitive, but also specific to event boundaries. We conclude that the hippocampus plays an important role in segmenting the continuous experience that is typical of naturalistic settings. Significance statementRecent years have seen the field of human neuroscience research transitioning from experiments with simple stimuli to the study of more complex and naturalistic experience. Nonetheless, our understanding of the function of many brain regions, such as the hippocampus, is based primarily on the study of brief, discrete events. As a result, we know little of what triggers hippocampal activity in real-life settings, when we are exposed to a continuous stream of information. When does the hippocampus "decide" to respond during the encoding of naturalistic experience? We reveal here that hippocampal activity measured by fMRI during film-watching is both sensitive and specific to event boundaries, identifying a potential mechanism whereby event boundaries shape experience by mod...

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Section: Discussionmentioning

confidence: 99%

The hippocampal film-editor: sensitivity and specificity to event boundaries in continuous experience

Ben-Yakov

Henson

2018

Preprint

143

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“…In line with this idea, several studies have implicated the human hippocampus in the maintenance of recently encountered stimuli (Axmacher et al, ; Piekema, Kessels, Mars, Petersson, & Fernandez, ). Weaving these strands together, one can speculate that the hippocampus creates a model of an ongoing event (Milivojevic, Varadinov, Vicente Grabovetsky, Collin, & Doeller, ) by disentangling overlapping elements of an event though pattern separation (Hunsaker & Kesner, ; Rolls, , ), maintaining these discrete elements for the duration of the event (e.g., Axmacher, Henseler, et al, 2010), and subsequently, binding these elements together into a coherent event representation (Schapiro, Turk‐Browne, Norman, & Botvinick, ; Staresina & Davachi, ).…”

Section: Episodic Memories Are Formed At Event Boundariesmentioning

confidence: 99%

Event conjunction: How the hippocampus integrates episodic memories across event boundaries

Griffiths

Fuentemilla

2019

Hippocampus

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Our lives are a continuous stream of experience. Our episodic memories on the other hand have a definitive beginning, middle, and end. Theories of event segmentation suggest that salient changes in our environment produce event boundaries which partition the past from the present and, as a result, produce discretized memories. However, event boundaries cannot completely discretize two memories; any shared conceptual link will lead to the rapid integration of these memories. Here, we present a new framework inspired by electrophysiological research that resolves this apparent contradiction. At its heart, the framework proposes that hippocampal theta‐gamma coupling maintains a highly abstract model of an ongoing event and serves to encode this model as an episodic memory. When a second but related event begins, this theta‐gamma model is rapidly reconstructed within the hippocampus where new details of the second event can be appended to the existing event model. The event conjunction framework is the first electrophysiological explanation of how event memories can be formed at, and integrated across, event boundaries.

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“…Interestingly, perceptual regions tended to identify a larger number of short events, presumably due to a greater sensitivity to rapidly changing environmental features. In a different study, the hippocampus was found to be sensitive to narrative context at an even coarser level than the PMN, separately representing two interleaved story lines [36*]. Thus, the hippocampus and PMN may support high-level structure, integrating within stable events and rapidly shifting when a new situation is encountered.…”

Section: Challenging Data: Can Context Shift Abruptly?mentioning

confidence: 99%

Does mental context drift or shift?

DuBrow

Rouhani

Niv

et al. 2017

Current Opinion in Behavioral Sciences

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Theories of episodic memory have generally proposed that individual memory traces are linked together by a representation of context that drifts slowly over time. Recent data challenge the notion that contextual drift is always slow and passive. In particular, changes in one’s external environment or internal model induce discontinuities in memory that are reflected in sudden changes in neural activity, suggesting that context can shift abruptly. Furthermore, context change effects are sensitive to top-down goals, suggesting that contextual drift may be an active process. These findings call for revising models of the role of context in memory, in order to account for abrupt contextual shifts and the controllable nature of context change.

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Coding of Event Nodes and Narrative Context in the Hippocampus

Cited by 69 publications

References 66 publications

The hippocampal film-editor: sensitivity and specificity to event boundaries in continuous experience

The hippocampal film-editor: sensitivity and specificity to event boundaries in continuous experience

Event conjunction: How the hippocampus integrates episodic memories across event boundaries

Does mental context drift or shift?

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