Memory reactivation during rest supports upcoming learning of related content

Abstract

Although a number of studies have highlighted the importance of offline processes for memory, how these mechanisms influence future learning remains unknown. Participants with established memories for a set of initial face-object associations were scanned during passive rest and during encoding of new related and unrelated pairs of objects. Spontaneous reactivation of established memories and enhanced hippocampal-neocortical functional connectivity during rest was related to better subsequent learning, specifically of related content. Moreover, the degree of functional coupling during rest was predictive of neural engagement during the new learning experience itself. These results suggest that through rest-phase reactivation and hippocampal-neocortical interactions, existing memories may come to facilitate encoding during subsequent related episodes.N umerous empirical studies (1-4) and theoretical accounts (5, 6) highlight the importance of offline processes-such as reinstatement of recent experience and enhanced interregional communication-for episodic memory. It has been proposed that through hippocampal (HPC)-neocortical interactions (6, 7), memories are reactivated during periods of sleep and awake rest. Such reactivation (or "replay") is thought to support the strengthening and transfer of memory traces from the HPC to neocortical regions for long-term storage, a process termed "consolidation." The functional significance of reactivation of recent experience for memory has been demonstrated during awake rest using neurophysiological techniques in rodents (2) and, more recently, in humans using pattern information analysis of functional magnetic resonance imaging (fMRI) data (1, 3). For instance, more delay period reactivation has been observed for stimuli that were remembered, relative to those that were forgotten in a subsequent test (3). Moreover, studies have shown that the degree of HPCneocortical functional coupling during rest periods following learning relates to later memory for the learned content (4).This existing body of work demonstrates that rest-phase neural signatures relate to memory for prior experiences. However, one important quality of memory is that it is inherently prospective (8); that is, memories are formed for maximal utility in future situations. Whereas research shows that rest-phase reactivation impacts memory for the reactivated content itself (1, 3), how this mechanism might be prospectively advantageous remains unknown. In the present study, we turn our attention to this question: How does spontaneous reactivation of established memories and enhanced HPC-neocortical connectivity during rest affect learning during subsequent related episodes?

Post-learning Hippocampal Dynamics Promote Preferential Retention of Rewarding Events

“…Previous studies in humans have demonstrated that post-learning reactivation events can be observed via multivariate pattern analyses on fMRI data (Deuker et al, 2013; Schlichting and Preston, 2014; Staresina et al, 2013). These studies have reported reactivation of specific items or item categories in entorhinal, retrosplenial, (Staresina et al (2013), and occipitotemporal cortex (Deuker et al, 2013; Schlichting and Preston, 2014), but reactivation has not been observed in the hippocampus.…”

“…These studies have reported reactivation of specific items or item categories in entorhinal, retrosplenial, (Staresina et al (2013), and occipitotemporal cortex (Deuker et al, 2013; Schlichting and Preston, 2014), but reactivation has not been observed in the hippocampus. In contrast, single-unit recording studies have only demonstrated hippocampal replay of spatial context information, with the strongest effects for place cell sequences associated with rewards.…”

“…For example, studies on resting-state functional connectivity (RSFC) have shown that post-learning RSFC between the hippocampus and category-selective cortical regions predicted subsequent memory for stimuli from those categories (Schlichting and Preston, 2014; Tambini et al, 2010; Tompary et al, 2015). Recent studies have also used fMRI data to show that neocortical representations of specific items or item categories are reactivated during post-learning rest (Deuker et al, 2013; Schlichting and Preston, 2014; Staresina et al, 2013). Although these studies suggest that neural processes that occur after learning can contribute to human memory, it is not clear how motivation influences post-learning activity in the hippocampus.…”

Decisions about the past are guided by reinstatement of specific memories in the hippocampus and perirhinal cortex

“…Given the established functional differences in lateral versus medial subregions of entorhinal cortex (ERC; e.g., Knierim et al, 2014) and the limited resolution of fMRI, we excluded ERC from our analyses. The segmentations were validated by two other expert raters and have been used in previous published studies (Schlichting and Preston, 2014; Schlichting et al, 2015). PRC was defined as the lateral and medial wall of the collateral sulcus and a 3mm wide transition zone between PHC and PRC was excluded from both regions.…”

Impact of smartphone use on quality of sleep among medical students

“…7 Episodic memories are gradually assimilated into longterm memory and this process is strongly influenced by sleep & existing memories are spontaneously reactivated and strengthened in the brain during rest periods. 8,9 Sleep problems and sleep deprivation lead to poor academic performance and excessive day time sleepiness in college students. 10,11 Since medical students are required to be alert & attentive during learning period so that they acquire professional level knowledge & skills of patient care, medical students who already have lots of academic burden and sleep problems due to other factors, smartphone overuse/addiction if present may further complicate the things and may lead to significant stress & mental health problems.…”