P2-466: hippocampus mediates the association between entorhinal cortex, basal forebrain and separation of spatial information in early clinical alzheimer's disease

The hippocampus, entorhinal cortex and basal forebrain (BF) are the first brain structures affected in Alzheimer's disease (AD) and play a key role in spatial memory and navigation. Spatial pattern separation is a process of maintaining non-overlapping representations of spatial locations for similar patterns of activation that is critical for accurate encoding of spatial information but is poorly understood in AD. Our objectives were to explore spatial pattern separation accuracy and its association with hippocampal, entorhinal cortical and BF volumes in the biomarker-defined early clinical stages of AD. Participants with amnestic mild cognitive impairment (aMCI) due to AD (n=44), mild AD dementia (n=31) and cognitively normal older adults (CN; n=23) underwent clinical and cognitive evaluation, MRI brain scan with hippocampal, entorhinal cortical and BF volumetric measurement, and spatial pattern separation assessment. The subjects were asked to remember the location of a blue circle on a computer screen and indicate after 20 second delay, which of the two simultaneously displayed circles was in the same location as the previously presented one. Four spatial separations between two circles were used: 0.0, 0.5, 1.0, and 1.5cm. The accuracy of spatial pattern separation performance decreased with AD severity (dementia