Lesser Neural Pattern Similarity across Repeated Tests Is Associated with Better Long-Term Memory Retention

Abstract

Encoding and retrieval processes enhance long-term memory performance. The efficiency of encoding processes has recently been linked to representational consistency: the reactivation of a representation that gets more specific each time an item is further studied. Here we examined the complementary hypothesis of whether the efficiency of retrieval processes also is linked to representational consistency. Alternatively, recurrent retrieval might foster representational variability-the altering or adding of underlying memory representations. Human participants studied 60 Swahili-Swedish word pairs before being scanned with fMRI the same day and 1 week later. On Day 1, participants were tested three times on each word pair, and on Day 7 each pair was tested once. A BOLD signal change in right superior parietal cortex was associated with subsequent memory on Day 1 and with successful long-term retention on Day 7. A representational similarity analysis in this parietal region revealed that beneficial recurrent retrieval was associated with representational variability, such that the pattern similarity on Day 1 was lower for retrieved words subsequently remembered compared with those subsequently forgotten. This was mirrored by a monotonically decreased BOLD signal change in dorsolateral prefrontal cortex on Day 1 as a function of repeated successful retrieval for words subsequently remembered, but not for words subsequently forgotten. This reduction in prefrontal response could reflect reduced demands on cognitive control. Collectively, the results offer novel insights into why memory retention benefits from repeated retrieval, and they suggest fundamental differences between repeated study and repeated testing.

Consolidation Promotes the Emergence of Representational Overlap in the Hippocampus and Medial Prefrontal Cortex

“…Most theories posit that the hippocampus orthogonalizes incoming information in order to avoid interference from related past experiences (O'Reilly and McClelland, 1994). Indeed, there is now a growing body of evidence for pattern separation signals in the hippocampus during encoding (Leutgeb et al, 2007; Bakker et al, 2008; LaRocque et al, 2013; Favila et al, 2016; Chanales et al, 2017) and work showing that variability in neural patterns across repeated testing is related to long-term retention (Wirebring et al, 2015). In the present experiment, hippocampal similarity across encoding was lower for overlapping trials relative to non-overlapping trials, consistent with this theoretical and empirical work.…”

Neural correlates of retrieval-based enhancement of autobiographical memory in older adults

“…Second, it is difficult to attribute the aforementioned accounts to specific neural processes in the ROIs. In order to examine the neural process of reactivation-based reconsolidation or retrieval-induced forgetting, one needs to track the brain activation patterns during encoding and training, and associate them with those collected during testing, as well as the memory outcome 34,69 , e.g., using representational similarity analysis 37,51,70,71 . However, due to operational constraints in the real-world, this study did not record neural process during encoding and training, making it impossible to check the reinstatement effect.…”

Weakly encoded memories due to acute sleep restriction can be rescued after one night of recovery sleep

“…According to the model of active system consolidation during sleep, recently encoded memories that are reactivated during subsequent sleep have a greater likelihood to undergo qualitative changes, making them stronger to interference and more resistant to forgetting 25,27,28,67 . If the reactivation of prior memories during SWS, indexed here by the degree of SO-SP coupling, leads to a transformation or elaboration of the memory representations, retrieval should be less dependent on the reinstatement of certain encoding processes 68 , especially those referred to reactivation of nonessential information. In line with this prediction, SO-SP coupling correlated negatively with the reinstatement of frontoparietal neural pattern of activity elicited at early stages of encoding.…”