Sleep Enhances Recognition Memory for Conspecifics as Bound into Spatial Context

Abstract

Social memory refers to the fundamental ability of social species to recognize their conspecifics in quite different contexts. Sleep has been shown to benefit consolidation, especially of hippocampus-dependent episodic memory whereas effects of sleep on social memory are less well studied. Here, we examined the effect of sleep on memory for conspecifics in rats. To discriminate interactions between the consolidation of social memory and of spatial context during sleep, adult Long Evans rats performed on a social discrimination task in a radial arm maze. The Learning phase comprised three 10-min sampling sessions in which the rats explored a juvenile rat presented at a different arm of the maze in each session. Then the rats were allowed to sleep (n = 18) or stayed awake (n = 18) for 120 min. During the following 10-min Test phase, the familiar juvenile rat (of the Learning phase) was presented along with a novel juvenile rat, each rat at an opposite arm of the maze. Significant social recognition memory, as indicated by preferential exploration of the novel over the familiar conspecific, occurred only after post-learning sleep, but not after wakefulness. Sleep, compared with wakefulness, significantly enhanced social recognition during the first minute of the Test phase. However, memory expression depended on the spatial configuration: Significant social recognition memory emerged only after sleep when the rat encountered the novel conspecific at a place different from that of the familiar juvenile in the last sampling session before sleep. Though unspecific retrieval-related effects cannot entirely be excluded, our findings suggest that sleep, rather than independently enhancing social and spatial aspects of memory, consolidates social memory by acting on an episodic representation that binds the memory of the conspecific together with the spatial context in which it was recently encountered.

Conspecific Presence Improves Episodic-Like Memory in Rats

“…In the context of episode configuration, some interesting assumptions arise. Sawangjit et al reported a study about the effects of sleep on memory formation, in which rats were exposed to a conspecific in different positions of a radial arm maze, and found that social and spatial aspects were bound into a single episode ( Sawangjit et al, 2017 ). Accordingly, it is reasonable to assume an integrated cognitive representation of the physical and social information in our experiment, where the dyad-mate forms part of the episode together with the features of the task.…”

Deepened sleep makes hippocampal spatial memory more persistent

“…In the main experiment, sleep was assessed using video recordings according to standard visual procedures (Pack et al, 2007;Sawangjit, Kelemen, Born, & Inostroza, 2017;Van Twyver, Webb, Dube, & Zackheim, 1973). In brief, sleep was scored whenever the rat showed a typical sleep posture and stayed immobile for at least 5 s. If brief movements interrupted sleep epochs by <5 s, continuous sleep was scored.…”

Prioritization of Sleep: Discrepancies Between Attitude and Practice

“…[12][13][14] Moreover, sleep deprivation also affects physical health, resulting in obesity, metabolic syndrome, and cardiovascular disease. [15][16][17] On the other hand, optimized sleep has been identified to be related to enhanced memory consolidation [18][19][20] and improved workplace performance. [21][22][23] Neuroscience research has demonstrated that sleep is important for the elimination of harmful proteins from the brain that may be related to the development of Alzheimer's disease.…”