Roles of human hippocampal subfields in retrieval of spatial and temporal context

Abstract

While numerous studies indicate the involvement of the hippocampus in encoding and retrieval of spatial and temporal context, the neural basis of spatial and temporal processing within the hippocampal circuit remains unclear. We employed a novel paradigm in which participants encoded stores within a spatial layout by visiting them in a specific temporal order. Participants then underwent high-resolution functional magnetic resonance imaging (fMRI) targeting the hippocampus while retrieving details of the spatial or temporal context in alternating blocks. During retrieval, participants made judgments about either near or far intervals within the spatial layout or temporal sequence. Across both near and far intervals, we found that retrieving spatial layout and temporal order information resulted in comparable levels of activation in the hippocampus that was not preferentially localized to a specific subfield. Furthermore, using a multivariate approach called multivariate pattern similarity analysis (MPSA), we found that correct near judgments vs. correct far judgments differed in their patterns of activity for spatial vs. temporal order judgments. Despite these differences in MPSA patterns, we did not find any specific subfields differentially recruited for spatial vs. temporal order retrieval. We discuss our results in terms of their relation to computational models of hippocampal subfield function and suggest mechanisms by which the hippocampus could process space and temporal order without the need for specific contributions from hippocampal subfields.

On the Integration of Space, Time, and Memory

“…During testing of memories for the distances and timing between key events, subject-specific neural similarity in the hippocampus scaled with the remembered proximity of events both in space and time. Notably, unlike in the Kyle et al (2015) report, in this study subjects’ judgments about space and time were correlated and the integrated spatial and temporal patterns did predict space and time judgments. However, there were also individual influences of spatial and temporal coding when the other variable was removed in the analysis, confirming a degree of independence between the neural ensemble patterns that represent space and time.…”

“…To explore potential differences among hippocampal subdivisions and whether space and time are represented by the same or different neural ensemble activity patterns, Kyle et al (2015) employed high-resolution fMRI on human subjects during memory retrieval after playing a virtual reality game where they visited stores in a particular order within a specific spatial layout. During retrieval participants made independent judgments either about near or far intervals within the spatial layout or about temporal sequence.…”

Temporal and spatial context in the mind and brain

“…This unified account of spatial context, temporal context and spatiotemporal context aligns well with recent fMRI studies virtual reality suggesting not only that similar regions participate in recovery of spatial and temporal context [66, 67, 64] (see also Fig. 2B).…”

Memory: Organization and Control

“…Successful memory was associated with maintenance during the delay of the same hippocampal activation pattern observed during encoding. Supporting theories about the importance of context coding, RSA studies have shown that successful memory is associated with reinstatement of the representation of the relevant spatial or temporal context occupied by the item during initial study (Flegal et al 2014, Kyle et al 2015; for reviews, see Davachi 2006, Eichenbaum et al 2007) and with increased dissimilarity of spatial and temporal context representations between memories (Copara et al 2014). …”