Probing the neural dynamics of mnemonic representations after the initial consolidation

Neuroimage. 2020 Nov 1:221:117213. doi: 10.1016/j.neuroimage.2020.117213. Epub 2020 Jul 31.

Abstract

Memories are not stored as static engrams, but as dynamic representations affected by processes occurring after initial encoding. Previous studies revealed changes in activity and mnemonic representations in visual processing areas, parietal lobe, and hippocampus underlying repeated retrieval and suppression. However, these neural changes are usually induced by memory modulation immediately after memory formation. Here, we investigated 27 healthy participants with a two-day functional Magnetic Resonance Imaging study design to probe how established memories are dynamically modulated by retrieval and suppression 24 h after learning. Behaviorally, we demonstrated that established memories can still be strengthened by repeated retrieval. By contrast, repeated suppression had a modest negative effect, and suppression-induced forgetting was associated with individual suppression efficacy. Neurally, we demonstrated item-specific pattern reinstatements in visual processing areas, parietal lobe, and hippocampus. Then, we showed that repeated retrieval reduced activity amplitude in the ventral visual cortex and hippocampus, but enhanced the distinctiveness of activity patterns in the ventral visual cortex and parietal lobe. Critically, reduced activity was associated with enhanced representation of idiosyncratic memory traces in the ventral visual cortex and precuneus. In contrast, repeated memory suppression was associated with reduced lateral prefrontal activity, but relative intact mnemonic representations. Our results replicated most of the neural changes induced by memory retrieval and suppression immediately after learning and extended those findings to established memories after initial consolidation. Active retrieval seems to promote episode-unique mnemonic representations in the neocortex after initial encoding but also consolidation.

Keywords: Consolidation; Episodic memory; Memory retrieval; Memory suppression; Pattern reinstatement.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Association Learning / physiology
  • Brain Mapping / methods*
  • Cerebral Cortex / diagnostic imaging
  • Cerebral Cortex / physiology*
  • Cues
  • Female
  • Hippocampus / diagnostic imaging
  • Hippocampus / physiology
  • Humans
  • Image Interpretation, Computer-Assisted
  • Magnetic Resonance Imaging
  • Male
  • Memory Consolidation / physiology*
  • Memory, Episodic*
  • Mental Recall / physiology*
  • Pattern Recognition, Visual / physiology
  • Spatial Memory / physiology
  • Support Vector Machine*
  • Young Adult