Do mice need NMDA receptors to complete a spatial memory from partial cues?

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Pattern completion is the retrieval of a complete memory initiated by a subset of external cues, and it has been a major focus of computational models. An earlier study reported that it requires NMDA receptors in the hippocampus. But that finding came from a non-inducible gene knockout experiment in which the receptors were absent throughout all stages of memory processing and the animals’ adult lives. This left open whether the receptors were actually needed during retrieval.

To test their role specifically at retrieval, the researchers used inducible knockout of NMDA receptors limited to the memory retrieval stage. In two independent mouse lines, mice lacking the receptors at retrieval in either the forebrain or the hippocampal CA1 region showed normal recall of associative spatial reference memory under both full-cue and partial-cue conditions.

Systemic antagonism of NMDA receptors during retention tests also had no effect on full-cue or partial-cue recall of spatial water maze memories. Together, the genetic and pharmacological experiments indicate that pattern completion during spatial associative memory recall does not require NMDA receptors in the hippocampus or forebrain.