DISTRACTOR LIST ERRORS FROM VERBAL LEARNING TEST MAY REVEAL DEFICIENT TEMPORAL MEMORY ENCODING IN PREDEMENTIA ALZHEIMER’S DISEASE

An integral part of episodic memory formation is our ability to register a detailed timeline of experienced events. Recent findings link the lateral entorhinal cortex (LEC) to temporal memory encoding in rodents. The entorhinal cortex is affected early in Alzheimer's disease (AD). Accordingly, deficient temporal memory encoding may be an early AD marker. Increased intrusion error rates are associated with predementia stages and progression to AD. A subset of these errors, putatively caused by confusion between two different word lists presented close in time, may represent incorrect encoding of temporal sequence. We investigate if subjects with subjective cognitive decline (SCD) and mild cognitive impairment (MCI) with amyloid plaques show increased distractor list intrusions (DLI) relative to other errors, consistent with a predementia AD-linked temporal encoding deficiency. We included 131 subjects from the Dementia Disease Initiation (DDI) cohort. Amyloid status was determined using CSF Aβ1-42 (denoted Aβ+ or Aβ-). The sample comprised n=23 healthy Aβ- controls (HC), cases with SCD (SCD-Aβ+, n=10; SCD-Aβ-, n=48) and MCI (MCI-Aβ+, n=21; MCI-Aβ-, n=29). Total DLI and total other intrusions from the Rey Auditory Verbal Learning Test (RAVLT) were compared between groups using Kruskal-Wallis analyses and Dunn's post-hoc pairwise comparisons. Using Spearman's rho, we correlated intrusion data with age, educational level, CSF Aβ1-42, total tau (t-tau) and phosphorylated tau (p-tau). No differences in DLI were found between HC and MCI-Aβ- subjects, but rates were increased in MCI-Aβ+ compared to HC (p<.01) and MCI-Aβ- subjects (p<.05). A non-significant trend for increased DLI was observed in SCD-Aβ+ subjects (figure 1, table 1). No group differences were found for rates of other intrusions. DLI correlated with lower CSF Aβ1-42 (r=−.246, p<.01) and higher CSF t-tau (r=.211, p<.05) and p-tau (r=.188, p<.05) levels, but not with age or educational level. In contrast, no significant correlations were found between other intrusions and CSF biomarkers, but for both increasing age (r=.183, p<.05) and lower educational level (r=−.161, p<.05).