0058 Neural Differentiation of Competing Memory Representations After a Prediction Error Depends on REM Sleep

Abstract Introduction When we retrieve a memory, competing memories can come to mind. One way the brain might resolve this competition is by pushing the interfering memory representations away from one another (neural differentiation). Previous work found that, when an item predicted in a particular context (A predicts B) failed to appear and was later restudied in a different context, the A and B representations became less similar in the hippocampus. We used fMRI to test the preregistered hypothesis that rapid eye movement (REM) sleep (occurring post-prediction-error) is required to observe this effect. Methods In the morning, we first obtained pre-learning fMRI “snapshots” of each item’s neural representation by extracting the spatial pattern of BOLD activity corresponding to each item. Next, participants viewed a continuous stream of scenes that, unbeknownst to them, followed a pair structure. Each pair had one scene as the first item (scene A) and a different scene as the second item (scene B). Each pair was shown together three times, inserted in the stream continuously amongst the other pairs, creating the expectation that B will follow A. For a subset of pairs, this expectation was then violated on trials where B failed to follow A; the B item was subsequently restudied on its own (i.e., not preceded by its pairmate A). Participants were then randomly assigned to remain awake, take a nap containing non-REM sleep only, or take a nap with both non-REM and REM sleep. Later the same day, we obtained post-learning fMRI snapshots of each item’s neural representation. Results We used pattern similarity analysis to compare the pre- and post-learning snapshots and found evidence of neural differentiation of the A and B items in the right CA2/3/DG subfield of the hippocampus, but only in the group whose nap contained REM sleep. Conclusion This result provides the first evidence linking REM sleep to changes in the hippocampal representations of specific memories in humans, and - more generally - suggests that REM helps to restructure neural representations in response to competition that occurs during wake. Support (if any) R01 MH06945 (K.A.N and N.T.-B.) K99 MH126154 (E.A.M.)