O005 Overnight Consolidation of Spatial Navigation Memories is Impaired in Mild Cognitive Impairment and is Associated with Loss of Sleep Spindles and Hippocampal Subfield Volumes

Abstract Introduction Allocentric spatial navigation (SN) is considered a measure for conversion from mild cognitive impairment (MCI) to Alzheimer’s disease. NREM sleep slow waves and spindles, and hippocampal volume (HV) are impaired in MCI, however their relationship with SN overnight memory consolidation (OMC) is unknown. This study aimed to examine: 1) SN OMC in MCI, and, 2) associations between SN OMC and NREM oscillations and HV. Methods Cognitively-intact (n=25), non-amnestic MCI (naMCI, n=22) and amnestic-MCI (aMCI, n=10) older adults completed neuropsychological assessment, neuroimaging, overnight routine and high-density EEG polysomnography (hdEEG subset; controls=17, MCI=8). Slow oscillations, slow wave activity, slow and fast spindle density and power were computed. OMC% was calculated by: ([post-sleep error score/pre-sleep error score]*100) from a familiar and novel (allocentric) location. Right CA1, dentate gyrus (DG) and entorhinal cortex were computed using ASHS software. Results MCI performed worse on familiar location-OMC% compared to controls (Cohens d= -.67, p= .016). aMCI performed worse on allocentric-OMC% compared to controls (omega2= .09, p= .032). Reduced spindles were associated with worse allocentric-OMC% in aMCI (frontal-slow spindles [rho= -.782 p= .008], parietal-fast spindles [rho= -.576, p= .082]). Using hdEEG, widespread fast spindle and allocentric-OMC% associations were indicated in MCI. Reduced right HV (DG [r= -.453, p= .023], CA1 [r= -.426, p= .068]) was related to worse allocentric-OMC% in MCI. Discussion In MCI, SN OMC is impaired, with worse consolidation associated with spindle and right HV loss. Future studies should examine whether SN OMC and spindles capture conversion to Alzheimer’s disease in ‘at-risk’ older adults.