[IC‐P‐061]: APOE4 EFFECT ON LONGITUDINAL VOLUMETRICS AND PIB ACCUMULATION IN PRECLINICAL ALZHEIMER DISEASE

performed a pattern separation paradigm using repeated, similar lures and novel foil items while being scanned in a 7T Siemens MRI scanner. We manipulated 4 levels of difficulty for similar lures (lures 1-4). For each subject, t-statistics were extracted in the hippocampal subfields using SPM12. We tested for group differences (APOE-e4 carriers vs. non-carriers) in novelty and pattern separation effects. Using representational similarity analysis (RSA), we investigated the correlation between first and second presentation of trials in each condition. We hypothesized that lower correlations reflect more distinct items representations, i.e. pattern separation. Results: Behaviourally, we found that APOE-e4 carriers as compared to non-carriers were less accurate in pattern separation of the most difficult lure1 items and were more likely to incorrectly label those lures as repeated items (Fig. 1A). In the fMRI data, we found a stronger novelty effect (first > repeat) in right DG of the APOE-e4 carriers as compared to non-carriers (Fig. 1Bi). We did not find any group differences for brain activity related to pattern separation (lure1 > repeat) (Fig. 1Bii). No significant differences in RSA patterns were found, due to the small sample size (Fig. 1C). Conclusions:Our analyses with a small group of participants reveal possible differences between APOE-e4 carriers and non-carriers in pattern separation in the DG and in other hippocampal subfields. References: 1. Yassa, M.A., et al., Neuroimage, 2010. 51(3): p. 1242-52. 2. Baker, S., et al., Curr Biol, 2016. 26(19): p. 26292634. 3.Berron, D., et al., J Neurosci, 2016. 36(29): p. 7569-79.