The function of the human hippocampus is normally investigated by experimental manipulation of discrete events. Less is known about what triggers hippocampal activity during more naturalistic, continuous experience. We hypothesized that the hippocampus would be sensitive to the occurrence of event boundaries, that is, moments in time identified by observers as a transition between events. To address this, we analyzed functional MRI data from two groups: one (n = 253, 131 female) who viewed an 8.5 min film and another (n = 15, 6 female) who viewed a 120 min film. We observed a strong hippocampal response at boundaries defined by independent observers, which was modulated by boundary salience (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. 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 hippocampal events and event boundaries was highly significant, revealing that the hippocampal response is not only sensitive, but also specific to event boundaries. We conclude that event boundaries play a key role in shaping hippocampal activity during encoding of naturalistic events.
Bibliographical noteFunding Information:
Received Feb. 26, 2018; revised July 2, 2018; accepted July 3, 2018. Author contributions: A.B.-Y. wrote the first draft of the paper; A.B.-Y. and R.N.H. edited the paper; A.B.-Y. and R.N.H. designed research; A.B.-Y. performed research; A.B.-Y. analyzed data; A.B.-Y. and R.N.H. wrote the paper. This work was supported by the UK Medical Research Council (Grant SUAG/010 RG91365) and a Marie Curie Individual Fellowship (705108) awarded to A.B.-Y. Data collection and sharing for this project was provided by Cam-CANandbythestudyforrestproject(http://www.studyforrest.org).Cam-CANfundingwasprovidedbytheUK Biotechnology and Biological Sciences Research Council (Grant BB/H008217/1), together with support from the UK Medical Research Council and the University of Cambridge. We thank Michael Hanke for help with the studyforrest dataset, Christopher Baldassano for support with the cortical pattern shift analysis, Becky Gilbert for statistical consultations,KatherineStorrsforhelpwiththeconvolutedneuralnetanalysis,andRoniTibon,AndreaGreve,Alex Kaula, and Alex Quent for valuable feedback. The authors declare no competing financial interests. Correspondence should be addressed to Aya Ben-Yakov, MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge CB2 7EF, UK. E-mail: firstname.lastname@example.org.
© 2018 Ben-Yakov et al.
- Event boundaries
- Long-term memory