Abstract
The ability to use stored information in a highly flexible manner is a defining feature of the declarative memory system. However, the neuronal mechanisms underlying this flexibility are poorly understood. To address this question, we recorded single-unit activity from the hippocampus of 2 nonhuman primates performing a newly devised task requiring the monkeys to retrieve long-term item-location association memory and then use it flexibly in different circumstances. We found that hippocampal neurons signaled both mnemonic information representing the retrieved location and perceptual information representing the external circumstance. The 2 signals were combined at a single-neuron level to construct goal-directed information by 3 sequentially occurring neuronal operations (e.g., convergence, transference, and targeting) in the hippocampus. Thus, flexible use of knowledge may be supported by the hippocampal constructive process linking memory and perception, which may fit the mnemonic information into the current situation to present manageable information for a subsequent action.
Highlights
Declarative memory enables individuals to remember past experiences or knowledge and to use that information according to a current situation [1, 2]
The present study aimed to investigate whether the flexible use of past knowledge can be explained by a constructive process in the HPC
We found a robust memory signal reflecting the location information retrieved from an item cue (Fig 2), which was substantial even after the onset of background cue
Summary
Declarative memory enables individuals to remember past experiences or knowledge and to use that information according to a current situation [1, 2]. This flexible use of stored information is in contrast to procedural or fear-conditioned memory, in which acquired memory is expressed in a fixed form of associated actions or physiological responses [3,4,5]. The mechanism by which the HPC contributes to the flexibility in the usage of the declarative memory remains largely unknown. The contributions of the HPC to the spatial memory task were successfully dissociated from those of the other brain areas when the start position in spatial mazes differed between training (e.g., “south” in a plus maze) and testing trials (e.g., “north”)
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