Impaired Hippocampal-Cortical Interactions during Sleep in a Mouse Model of Alzheimer’s Disease

• Published in: Current biology 2020-07, Vol.30 (13), p.2588-2601.e5
• Main Authors: Cushing, Sarah D., Skelin, Ivan, Moseley, Shawn C., Stimmell, Alina C., Dixon, Jessica R., Melilli, Andreza S., Molina, Leonardo, McNaughton, Bruce L., Wilber, Aaron A.
• Format: Article
• Language: English
• Subjects: Alzheimer Disease - physiopathology; Alzheimer's disease; Animals; Disease Models, Animal; Female; hippocampal-cortical dynamics; hippocampus; Hippocampus - physiopathology; Memory Consolidation; Memory Disorders - physiopathology; memory reactivation; memory replay; Mice; Mice, Transgenic; Neocortex - physiopathology; parietal cortex; sharp wave ripples; Sleep; Spatial Memory; spatial orientation
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2020.04.087

Spatial learning is impaired in humans with preclinical Alzheimer’s disease (AD). We reported similar impairments in 3xTg-AD mice learning a spatial reorientation task. Memory reactivation during sleep is critical for learning-related plasticity, and memory consolidation is correlated with hippocampal sharp wave ripple (SWR) density, cortical delta waves (DWs), cortical spindles, and the temporal coupling of these events—postulated as physiological substrates for memory consolidation. Further, hippocampal-cortical discoordination is prevalent in individuals with AD. Thus, we hypothesized that impaired memory consolidation mechanisms in hippocampal-cortical networks could account for spatial memory deficits. We assessed sleep architecture, SWR-DW dynamics, and memory reactivation in a mouse model of tauopathy and amyloidosis implanted with a recording array targeting isocortex and hippocampus. Mice underwent daily recording sessions of rest-task-rest while learning the spatial reorientation task. We assessed memory reactivation by matching activity patterns from the approach to the unmarked reward zone to patterns during slow-wave sleep (SWS). AD mice had more SWS, but reduced SWR density. The increased SWS compensated for reduced SWR density so there was no reduction in SWR number. In control mice, spindles were phase-coupled with DWs, and hippocampal SWR-cortical DW coupling was strengthened in post-task sleep and was correlated with performance on the spatial reorientation task the following day. However, in AD mice, SWR-DW and spindle-DW coupling were impaired. Thus, reduced SWR-DW coupling may cause impaired learning in AD, and spindle-DW coupling during short rest-task-rest sessions may serve as a biomarker for early AD-related changes in these brain dynamics. •In 3xTg-AD mice, increased sleep may compensate for some impaired brain dynamics•Hippocampal-cortical coupling increases after spatial task•Deficits in spatial learning and hippocampal-cortical coupling in 3xTg-AD mice•Spindle-Delta coupling deficits in cortex parallels hippocampal-cortical deficits Benthem et al. use multi-site recordings to demonstrate increased sleep in AD mice, which may compensate for some impaired brain dynamics. Hippocampal-cortical coupling during sleep predicts spatial learning in normal mice. However, spatial learning and hippocampal-cortical coupling are impaired in AD mice, possibly causing impaired learning.