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

INTRODUCTION: 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.