Representations of complex contexts: A role for hippocampus

Abstract

The hippocampus plays a critical role in supporting episodic memory. 7Although we know that temporal context is a defining feature of episodic memory, we 8understand relatively little about how this information may be represented by the 9 hippocampus. Research in rodents has suggested that the hippocampus represents 10 temporal information on an absolute scale or in terms of relative temporal intervals, but 11 cognitive models of memory have argued that temporal context in episodic memory is a 12 consequence of changes in cognitive states and experiences. Here, we combined high-13resolution fMRI imaging with voxel pattern similarity analyses to answer the question of 14 how human hippocampal subfields represent retrieved information about cognitive 15 states and the time at which a past event took place. As participants recollected 16 previously presented items, activity patterns in the CA23DG subregion carried 17 information about prior cognitive states, along with coarse-grained information about 18 when the item was previously encountered. These findings are consistent with the idea 19

Memory out of context: Spacing effects and decontextualization in a computational model of the medial temporal lobe

“…EC may support judgments of temporal duration (Lositsky et al, 2016), and anterolateral EC (alEC) (the analogue of LEC that can be measured in human fMRI) may aid in recalling the temporal context of a movie (Montchal, Reagh, & Yassa, 2019) and representing the temporal proximity of experience during learning (Bellmund, Deuker, & Doeller, 2019). Additionally, HC in fMRI is sensitive to short temporal durations (Barnett, O'Neil, Watson, & Lee, 2014), temporal proximity (Dimsdale-Zucker et al, 2020;Ezzyat & Davachi, 2014), sequences (Hsieh, Gruber, Jenkins, & Ranganath, 2014), and the time since encoding (Jenkins & Ranganath, 2010;Nielson et al, 2015). Altogether, these results suggest that the neural substrate for representing the temporal context of episodes, as simulated in computational models, may be instantiated in LEC and HC [see also Noulhiane, Pouthas, Hasboun, Baulac, and Samson (2007)].…”

“…We propose that time is a weak signal if not given prioritized attention. That is, the ability to reconstruct the past in a direct linear order when one is not intending to or does not encode a set of causally connected events in a linear order is poor (Dimsdale-Zucker et al, 2020), but not zero (Dester et al, 2021;Healey, 2018). Even in a rodent experiment that showed robust decoding of trial number from LEC neurons, when a task change eliminated the need to keep track of different trials, the ability to decode trial number from the neurons was reduced, but not eliminated [Figure 8 experiments, Tsao et al (2018)].…”