Targeted Memory Reactivation during Sleep Adaptively Promotes the Strengthening or Weakening of Overlapping Memories

Abstract

System memory consolidation is conceptualized as an active process whereby newly encoded memory representations are strengthened through selective memory reactivation during sleep. However, our learning experience is highly overlapping in content (i.e., shares common elements), and memories of these events are organized in an intricate network of overlapping associated events. It remains to be explored whether and how selective memory reactivation during sleep has an impact on these overlapping memories acquired during awake time. Here, we test in a group of adult women and men the prediction that selective memory reactivation during sleep entails the reactivation of associated events and that this may lead the brain to adaptively regulate whether these associated memories are strengthened or pruned from memory networks on the basis of their relative associative strength with the shared element. Our findings demonstrate the existence of efficient regulatory neural mechanisms governing how complex memory networks are shaped during sleep as a function of their associative memory strength. Numerous studies have demonstrated that system memory consolidation is an active, selective, and sleep-dependent process in which only subsets of new memories become stabilized through their reactivation. However, the learning experience is highly overlapping in content and thus events are encoded in an intricate network of related memories. It remains to be explored whether and how memory reactivation has an impact on overlapping memories acquired during awake time. Here, we show that sleep memory reactivation promotes strengthening and weakening of overlapping memories based on their associative memory strength. These results suggest the existence of an efficient regulatory neural mechanism that avoids the formation of cluttered memory representation of multiple events and promotes stabilization of complex memory networks.

Stimulation augments spike sequence replay and memory consolidation during slow-wave sleep

“…However, the changes were more significant in the experiments with sensory cue stimulation (Fig. 2f, right) where the greater amount of slow oscillations was found to be elicited with the targeted sound compared to the experiments with a control new sound (Oyarzun et al, 2017). To examine whether the enhanced performance in our simulations was merely due to the higher Up state count, we reduced the sleep duration from 300s to 260s for the cued sleep to obtain comparable Up state count to the uncued sleep.…”

“…presumably enhance reactivation of the relevant neuronal representations that improves memory consolidation. TMR was shown to improve both hippocampus-independent procedural memories (Antony et al, 2012;Schonauer, Geisler and Gais, 2014;Cousins et al, 2014;Cousins et al, 2016) and hippocampus-dependent declarative memories (Rudoy et al, 2009;Rasch et al, 2007;Batterink, Creery and Paller, 2016;Oyarzun et al, 2017). In one experiment, an odor was associated with learning a spatial card location task; subsequent presentation of the odor cue during sleep led to selective enhancement of this memory compared to the sleep without cueing (Rasch et al, 2007).…”

“…Specifically, the closed-loop stimulation presented during Down state, just before transition from Down to Up state of slow oscillation, had high impact on memory consolidation compared to the other stimulation phase. For overlapping memories, whether the auditory cues strengthen or weaken a memory also depended on the memory strength (Oyarzun et al, 2017). Notably, the beneficial effect of external reactivation only occurred during sleep.…”

Reactivating vocabularies in the elderly

“…6 Hz) and spindle band (ca. 13 Hz) (Groch, Schreiner, Rasch, Huber, & Wilhelm, 2016;Lehmann, Schreiner, Seifritz, & Rasch, 2016;Oyarzún, Morís, Luque, de Diego-Balaguer, & Fuentemilla, 2017;Schreiner, Lehmann, & Rasch, 2015). According to our working model, increase in the theta band might reflect successful reinstatement of memory traces by cueing during sleep, whereas increased activity in the spindle band relates to processes of integration and stabilization of memories after reinstatement of the memory trace by the cue ).…”

Shaping memory consolidation via targeted memory reactivation during sleep

“…The authors suggested that the stimulation of some low‐value items could have led to a generalized reactivation for the whole category of low‐value items. More recently, Oyarzún and colleagues used the same visuospatial location task to test the effect of TMR on overlapping memories. Specifically, participants had to initially learn the location of 15 card‐pairs (set X1–X2) and after 5 min (contiguous condition) or 3 h (delayed condition), they were asked to encode the location of a second set of 15 card‐pairs (set X1–X3).…”