Quent, J. A. | bioRxiv Science

bioRxiv2026

CA1 reinstatement and novelty response independently support recognition memory

One of the central tensions in memory research is whether consistency or differentiation across events is beneficial for remembering. While theoretical models posit that the hippocampal subfield CA1 subserves both types of computations, it remains unclear how it can simultaneously express both in service of recognition memory. Here, we contrasted the two prominent functions of CA1: reinstatement (consistency) and novelty processing (differentiation) to address this gap. To this end, we analysed the Natural Scenes Dataset featuring eight participants who completed a continuous recognition memory task spanning 41 separate days with 213,000 trials in total. We calculated reinstatement and novelty indices for each image and then examined the degree to which these reflected successful memory encoding. We found that CA1 showed evidence for encoding-related reinstatement as well as for novelty processing even after controlling for each other. Reinstatement was specific to retrieving the initial representation during the first retrieval attempt and did not extend to other forms of reinstatement. Exploratory analyses additionally identified reinstatement in CA3, which exhibited different response profiles compared to CA1. Our work thus highlights that computations of consistency as well as differentiation can be orthogonal signals contributing independently to memory success and can simultaneously co-exist within the same region of the hippocampus.

neuroscience↗

bioRxiv2026

Hippocampal subfields support human novelty detection via distinct signals

Detecting novelty is fundamental to adaptive memory, yet the neural comparisons that allow new events to be distinguished from prior experience are not fully understood. Hippocampal novelty signals are often framed as associative comparator responses that register violations of learned relationships. However, recognition memory models also predict a broader form of comparison: a global, item-based mismatch between an incoming stimulus and aggregate memory traces. Whether such global matching is implemented within human hippocampal circuitry, and whether it contributes to memory decisions, remains unknown. Using ultra-high-field 7T fMRI during dense sampling of a continuous object recognition task (76,800 trials across five sessions), we estimated both univariate novelty responses and multivariate global mismatch signals across hippocampal subfields. CA1 carried the novelty response that most reliably predicted accurate novelty detection, whereas the subiculum expressed a global mismatch signal that predicted detection independently of CA1. This subicular signal also shaped subsequent recognition behaviour, in which low global mismatch was associated with false alarms to novel objects that propagated into later hits. Finally, subicular global mismatch scaled with the experienced similarity of past events, consistent with an item-based comparison against accumulated memory. These findings identify distinct hippocampal mismatch signals for novelty detection and extend the human hippocampal comparator role beyond local associative mismatch to include global, item-based matching.

neuroscience↗