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The ability to navigate oneself in space is one of the first functional impairments in Alzheimer’s disease (AD). A 3D-computerised spatial navigation (SN) task was designed to delineate, for the first time in a sleep-dependent memory paradigm, egocentric and allocentric SN, the latter identified as one cognitive biomarker of AD. We examined group differences in SN memory and associations with sleep macroarchitecture. Methods Older adults with mild cognitive impairment (MCI, n=32) and controls (n=25) underwent overnight polysomnography and completed the SN task before and after sleep. Participants learnt the location of a target over 5 trials (familiar location; egocentric-dependent), then were instructed to find the target from a novel start location (allocentric-dependent). Memory % retention (MR) from both start locations were calculated by the XY coordinate of marked location to correct location of the target, pre- and post-sleep. Navigational strategies were coded using self-reported description of how participants’ found the target. Associations between MR with REM and SWS % duration, and AHI in REM and NREM were examined using Spearman’s correlations. Results Repeated-measures ANOVA showed Controls MR improved overnight whereas MCI performed worse (F=7.46, p=.009), with greatest differences on familiar start location MR (p=.02). Strategy as a covariate revealed a location by strategy interaction (p=01). Novel location MR was associated with REM%, rho=.448, (p=.02) in Controls, and REM-AHI, rho=.400 (p=.02) in MCI. Conclusion Behavioural and self-reported results suggest disrupted SN strategies relative to environment in MCI. Future studies should examine SN in association with sleep-wake neurophysiology and neuronal integrity.

sleep advances

P050 Familiar locations and new locations: sleep’s role in the consolidation of spatial navigation information using a novel virtual Morris water maze task in older adults with mild cognitive impairment