Memory hierarchies map onto the hippocampal long axis in humans

Abstract

Memories, like the internal representation of space, can be recalled at different resolutions ranging from detailed events to more comprehensive, multi-event narratives. Single-cell recordings in rodents indicate that different spatial scales are represented as a gradient along the hippocampal axis. Here, we show that a similar organisation holds for human episodic memory: memory representations systematically vary in scale along the hippocampal long-axis, which may enable the formation of mnemonic hierarchies.

Knowing what from where: Hippocampal connectivity with temporoparietal cortex at rest is linked to individual differences in semantic and topographic memory

“…Anterior hippocampus showed stronger connectivity with inferior frontal and lateral temporal cortex: meta-analytic decoding revealed functional labels including emotion, sensori-motor and autobiographical memory. These patterns are consistent with recent evidence demonstrating that anterior hippocampus codes memories with a coarser granularity than occurs towards the posterior extension (Collin, Milivojevic, & Doeller, 2015). In contrast, posterior hippocampal regions were more strongly connected to posterior regions of the neocortex including occipital and parietal cortex.…”

Dynamic updating of hippocampal object representations reflects new conceptual knowledge

“…It is noteworthy that our findings were localized to the anterior portion of the HPC. Recent rodent (38) and human (8,54) evidence suggests episodic memories are encoded according to a gradient of generalization along the HPC anterior-posterior axis. Posterior HPC has been shown to exhibit distinct representations for individual episodes, whereas anterior HPC codes for integrated representations that generalize across related episodes (8,22,38,54).…”

“…Recent rodent (38) and human (8,54) evidence suggests episodic memories are encoded according to a gradient of generalization along the HPC anterior-posterior axis. Posterior HPC has been shown to exhibit distinct representations for individual episodes, whereas anterior HPC codes for integrated representations that generalize across related episodes (8,22,38,54). The current study builds on these observations to show that anterior HPC representations are not limited to spatial contexts (19,38,55,56) or overlap between related episodes (8), but can also integrate attention-weighted object information across extended learning experiences.…”

Topographic separation of fornical fibers associated with the anterior and posterior hippocampus in the human brain: An MRI‐diffusion study

“…Of the two areas, the anterior hippocampus has been more linked to stress, anxiety, and emotional processing (Bannerman et al., 1999; Chase et al., 2015; O'Mara, 2005), whereas the posterior hippocampus is more typically linked to fine‐grain spatial processing (Poppenk et al., 2013; Strange et al., 2014). These differences do not, however, reflect a dichotomy, rather a gradation of change along the anterior–posterior axis (Collin et al., 2015; Poppenk et al., 2013; Strange et al., 2014). One interpretation is that the anterior hippocampus is important for forming large‐scale representations of the environment, whereas the posterior hippocampus provides more detailed representations (Poppenk et al., 2013; Strange et al., 2014).…”

“…Despite the role of this tract in cognition, surprisingly little is understood about the organization of the fibers within the human fornix and how this might relate to its various connections. The principal motivation to examine their topography arises from the growing evidence for functional differences along the anterior–posterior axis of the hippocampus (Collin, Milivojevic, & Doeller, 2015; Fanselow & Dong, 2010; Poppenk, Evensmoen, Moscovitch, & Nadel, 2013; Strange, Witter, Lein, & Moser, 2014). For instance, evidence from functional neuroimaging studies suggests a role of the posterior hippocampus in spatial navigation (e.g., Hartley, Maguire, Spiers, & Burgess, 2003), whereas anterior hippocampus has been associated with goal‐directed spatial decision making (Viard, Doeller, Hartley, Bird, & Burgess, 2011).…”