Sleep-dependent memory consolidation in infants protects new episodic memories from existing semantic memories

Manuela Friedrich,Jan Born,Matthias Mölle,Angela D Friederici

doi:10.1038/s41467-020-14850-8

Abstract

Any experienced event may be encoded and retained in detail as part of our episodic memory, and may also refer and contribute to our generalized knowledge stored in semantic memory. The beginnings of this declarative memory formation are only poorly understood. Even less is known about the interrelation between episodic and semantic memory during the earliest developmental stages. Here, we show that the formation of episodic memories in 14- to 17-month-old infants depends on sleep, subsequent to exposure to novel events. Infant brain responses reveal that, after sleep-dependent consolidation, the newly stored events are not processed semantically, although appropriate lexical-semantic memories are present and accessible by similar events that were not experienced before the nap. We propose that temporarily disabled semantic processing protects precise episodic memories from interference with generalized semantic memories. Selectively restricted semantic access could also trigger semantic refinement, and thus, might even improve semantic memory.

Highlights

Any experienced event may be encoded and retained in detail as part of our episodic memory, and may refer and contribute to our generalized knowledge stored in semantic memory
Repeated measures analysis of variance (ANOVA) of the event-related potentials (ERPs) to words presented during the memory test revealed processing differences between infant brain responses to incorrectly and correctly paired words (Semantic Congruity F1,58 = 7.625, P = 0.008, ηp2 = 0.116, Semantic Congruity × Region F1,58 = 16.143, P = 0.0002, ηp2 = 0.218, Semantic Congruity × Laterality F2,116 = 5.655, P = 0.007, ηp2 = 0.089), which to the greatest part reflects the expected N400 semantic context effect
This neural correlate of infant episodic memory, which we termed fronto-temporal memory response (FTMR), was clearly distinct from the neural correlate of semantic memory, the N400 response dominating over the parietal cortex

Summary

Introduction

Any experienced event may be encoded and retained in detail as part of our episodic memory, and may refer and contribute to our generalized knowledge stored in semantic memory. The beginnings of this declarative memory formation are only poorly understood. We show that the formation of episodic memories in 14- to 17-month-old infants depends on sleep, subsequent to exposure to novel events. The less generalized knowledge is available for novel experience—either in semantic long-term memory or transiently formed during encoding—the higher the central-parietal spindle activity in a subsequent nap. The higher the spindle activity during the nap, the stronger the semantic generalization of the novel experience in the memory test on a day[30]

Methods

Results

Conclusion