Thalamocortical spindles relate to changes in memory representations
Emily Cowan1, Anli Liu2, Simon Henin2, Sanjeev Kothare2, Orrin Devinsky2, Lila Davachi1; 1New York University, 2NYU Langone School of Medicine
It has long been hypothesized that sleep supports overnight memory consolidation. Features in the architecture of sleep have been related to sleep-dependent memory enhancements, including a relationship between specific stages of sleep and changes in univariate fMRI activation in the hippocampus and cortex during retrieval of memories learned before sleep. Evidence also suggests that functional connectivity measures may be time-sensitive, linking consolidation and the distribution of memory traces. However, it remains unknown how aspects of sleep architecture might relate to the representation of individual memory traces after sleep. To investigate this relationship, we designed a three-day experiment utilizing overnight polysomnography recordings and fMRI. Subjects encoded two lists of word-image pairs twice, either with an intervening period of overnight sleep (Sleep List), or a brief wakeful period (New List), such that the lists differed in the opportunity for consolidation. During the re-study scanning session, subjects were presented with previously seen word-image pairs, and new pairs (Single Study List). Cued recall was probed immediately following the scan and after a 24-hour delay. We found evidence that the density of thalamocortical fast spindles during overnight sleep was related to both the representation and distribution of the memories encoded prior to sleep. Specifically, in the ventromedial prefrontal cortex, fast spindle density was related to greater multivariate pattern similarity amongst Sleep List pairs. Spindle density also was related to functional connectivity between the anterior hippocampus and vmPFC, only for pairs learned before sleep, providing evidence that spindles promote a hippocampal-cortical dialogue during sleep-dependent consolidation.
Topic Area: LONG-TERM MEMORY: Episodic