Non-Interfering Effects of Active Post-Encoding Tasks on Episodic Memory Consolidation in Humans.

Samarth Varma,Lily Fu,W Pieter Medendorp,Sander Krewinkel,Maaike Van Kooten,Sander M Daselaar,Roy P C Kessels,Atsuko Takashima

doi:10.3389/fnbeh.2017.00054

Abstract

So far, studies that investigated interference effects of post-learning processes on episodic memory consolidation in humans have used tasks involving only complex and meaningful information. Such tasks require reallocation of general or encoding-specific resources away from consolidation-relevant activities. The possibility that interference can be elicited using a task that heavily taxes our limited brain resources, but has low semantic and hippocampal related long-term memory processing demands, has never been tested. We address this question by investigating whether consolidation could persist in parallel with an active, encoding-irrelevant, minimally semantic task, regardless of its high resource demands for cognitive processing. We distinguish the impact of such a task on consolidation based on whether it engages resources that are: (1) general/executive, or (2) specific/overlapping with the encoding modality. Our experiments compared subsequent memory performance across two post-encoding consolidation periods: quiet wakeful rest and a cognitively demanding n-Back task. Across six different experiments (total N = 176), we carefully manipulated the design of the n-Back task to target general or specific resources engaged in the ongoing consolidation process. In contrast to previous studies that employed interference tasks involving conceptual stimuli and complex processing demands, we did not find any differences between n-Back and rest conditions on memory performance at delayed test, using both recall and recognition tests. Our results indicate that: (1) quiet, wakeful rest is not a necessary prerequisite for episodic memory consolidation; and (2) post-encoding cognitive engagement does not interfere with memory consolidation when task-performance has minimal semantic and hippocampally-based episodic memory processing demands. We discuss our findings with reference to resource and reactivation-led interference theories.

Highlights

There is general consensus that wakeful rest after learning aids retention of episodic memories in humans—being able to remember our own personal past
From the associative recognition task, hit rates of each list were calculated separately by dividing the number of correctly identified ‘‘old/identical’’ items by the Results show that the two post-encoding delay periods did not differ in terms of subsequent memory performance: memory traces encoded prior to the 2-Back task underwent the same degree of consolidation as those encoded prior to rest
Our findings indicate that across different versions of the post-encoding n-Back task, subsequent memory performance did not differ from an equivalent period of post-encoding rest, thereby suggesting that the items learned prior to these two distinct brain states achieved the same degree of memory consolidation

Summary

Introduction

There is general consensus that wakeful rest after learning aids retention of episodic memories in humans—being able to remember our own personal past. During the post-learning rest period, recently acquired memories spontaneously reactivate by a replay of neuronal ensembles, triggered by hippocampal activity induced during the learning experience (Axmacher et al, 2008; Ego-Stengel and Wilson, 2009; Carr et al, 2011). Such reactivation of synaptic connections and circuits involved. Studies in the consolidation research domain find that quiet wakeful rest periods after learning promote better memory retention, but presenting intervening cognitive tasks containing meaningful content causes forgetting by ‘‘retroactive interference’’ (Lechner et al, 1999; Dewar et al, 2009)

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Conclusion