Abstract
BackgroundDuring permanent memory formation, recall of acquired place memories initially depends on the hippocampus and eventually become hippocampus-independent with time. It has been suggested that the quality of original place memories also transforms from a precise form to a less precise form with similar time course. The question arises of whether the quality of original place memories is determined by brain regions on which the memory depends.ResultsTo directly test this idea, we introduced a new procedure: a non-associative place recognition memory test in mice. Combined with genetic and pharmacological approaches, our analyses revealed that place memory is precisely maintained for 28 days, although the recall of place memory shifts from hippocampus-dependent to hippocampus-independent with time. Moreover, the inactivation of the hippocampal function does not inhibit the precision of remote place memory.ConclusionThese results indicate that the quality of place memories is not determined by brain regions on which the memory depends.
Highlights
The hippocampus is a key brain structure for learning and memory [1,2,3]
Using a contextual fear conditioning paradigm, which is an associative learning between a place and aversive experience, some studies demonstrated that the hippocampus is always necessary for the precision of place memories [13,14], supporting the memory transformation view [11] in which the quality of place memory correlates with the brain region on which that memory depends
We further examined the precision of their remote place memory in a variable-rooms/constant-chamber condition, in which mice were placed for 6 minutes in the S chamber in room A and 28 days later these mice were placed in the same S chamber in a different room B (Figure 3A)
Summary
The hippocampus is a key brain structure for learning and memory [1,2,3]. Recall of some associative and spatial memories initially depends on the hippocampus, but that hippocampal dependency progressively decays over time, a process that is associated with a gradual increase of neocortex-dependency [4,5,6,7,8,9]. Using a contextual fear conditioning paradigm, which is an associative learning between a place and aversive experience, some studies demonstrated that the hippocampus is always necessary for the precision of place memories [13,14], supporting the memory transformation view [11] in which the quality of place memory correlates with the brain region on which that memory depends. Another study demonstrated that the hippocampus is not required for memory precision after the passage of time [15], supporting the memory reorganization view [9] in which the quality of place memory does not correlate with the brain region This discrepancy can be attributed to differences in experimental protocols used for association with fear [15]. The question arises of whether the quality of original place memories is determined by brain regions on which the memory depends
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