On the Integration of Space, Time, and Memory

Abstract

The hippocampus is famous for mapping locations in spatially organized environments and several recent studies have shown that hippocampal networks also map moments in temporally organized experiences. Here I consider how space and time are integrated in the representation of memories. The brain pathways for spatial and temporal cognition involve overlapping and interacting systems that converge on the hippocampal region. There is evidence that spatial and temporal aspects of memory are processed somewhat differently in the circuitry of hippocampal subregions but become fully integrated within CA1 neuronal networks as independent, multiplexed representations of space and time. Hippocampal networks also map memories across a broad range of abstract relations among events, suggesting that the findings on spatial and temporal organization reflect a generalized mechanism for organizing memories.

Time, memory, and the legacy of Howard Eichenbaum

“…The results revealed that both of these variables independently contributed to the firing of most CA1 units, suggesting that the hippocampus encodes both spatial and temporal information. This finding suggests that hippocampal ensembles carry a multiplexed representation that could be used to localize an event in time, space, or both (Eichenbaum, ). The findings of time cells in rodents appear to generalize to primates.…”

“…Mankin and colleagues (Mankin et al, ; Mankin, Diehl, Sparks, Leutgeb, & Leutgeb, ) extended these findings by demonstrating that the ensemble code for spatial location in CA1 drifts considerably across successive days (see also Rubin, Geva, Sheintuch, & Ziv, , for similar findings; Ziv et al, ), and in area CA2, population codes changed considerably over the course of hours. These findings suggest that temporal context might be an important mechanism by which the hippocampus may support episodic memory (Eichenbaum, ; Ekstrom & Ranganath, ; Ranganath & Hsieh, ). For example, temporal drift in hippocampal coding could allow the hippocampus to assign different representations to successive events that occurred in the same spatial context (e.g., last night's dinner party vs. last month's dinner party).…”

Three brain states in the hippocampus and cortex

“…To specify, episodic memory involves (a) single episodes encompassing longer periods of time (seconds to minutes and longer) (Ferbinteanu, Kennedy, & Shapiro, ; Shapiro, Kennedy, & Ferbinteanu, ; Smith & Mizumori, ), (b) knowledge of temporal relationships across episodes, and (c) retrieval of episodes long after initial storage. Although recent work has provided promising clues (Attardo, Fitzgerald, & Schnitzer, ; Cai et al, ; Driscoll, Pettit, Minderer, Chettih, & Harvey, ; Eichenbaum, ; Eichenbaum, ; Eichenbaum, ; Ezzyat & Davachi, ; Ferbinteanu & Shapiro, ; Frank, Stanley, & Brown, ; Hsieh, Gruber, Jenkins, & Ranganath, ; Karlsson & Frank, ; Kitamura et al, ; Ludvig, ; Mankin et al, ; Mankin et al, ; Manning, Polyn, Baltuch, Litt, & Kahana, ; Manns, Howard, & Eichenbaum, ; Murray et al, ; Ranganath & Hsieh, ; Rubin, Geva, Sheintuch, & Ziv, ; Runyan, Piasini, Panzeri, & Harvey, ; Suh, Rivest, Nakashiba, Tominaga, & Tonegawa, ; Ziv et al, ), the neural representation of events at longer timescales remains unclear. More knowledge and insight are needed.…”

The intersection between the oculomotor and hippocampal memory systems: empirical developments and clinical implications

“…The hippocampus has a critical role in binding incoming information (including semantic and episodic information and without regard to conscious awareness of the incoming information) into lasting relational representations. The information that is bound by the hippocampus is received from broader MTL structures . The perirhinal cortex (PRC), entorhinal cortex (ERC), and parahippocampal cortex (PHC)—brain regions located within the MTL—support representations of items composed of complex combinations of features, the configural arrangement of features within and among items, and the broader spatial and nonspatial context of the surrounding environment, respectively.…”