Impact of contextual novelty on memory performance of patients with amnestic mild cognitive impairment

Abstract

Novelty detection and processing play a critical role in memory, so that new information is better remembered than familiar information. However, few studies have been conducted on how novelty influences the functioning of memory in Alzheimer's disease (AD) and more specifically its early stage, Mild Cognitive Impairment (MCI). The purpose of this study was to explore the impact of contextual novelty detection and processing on MCI patients’ memory. Twenty healthy older participants and 20 MCI patients performed a task based on the von Restorff paradigm. This task consisted of 25 lists of 10 words. For 20 lists, one word was salient because it had a larger font size (60 for non-target words and 90, 120 or 150 for target words). After each list, participants had to perform a free recall task. The effect of novelty (or VR effect) was calculated by a VRratio based on the percentage of target words recalled and the percentage of non-target words recalled. We also collected neuroimaging data to determine if there is a correlation between hippocampal size and the effect of novelty, given that the hippocampus is atrophied in MCI patients and typically involved in the processing of novelty. The analysis of VRratio (ANOVA 2 (groups) x 3 (font size) with repeated measures on the last variable) showed an effect of the font size but no effect of groups. Participants recalled more target words written in font size 120 and 150 compared to font size 90. Furthermore, Pearson correlation analysis demonstrated a positive correlation between the novelty effect for font size 120 and the right and left hippocampal volumes. This study indicates that MCI patients are able to detect and process novelty, at least contextual novelty as assessed here. However, novelty did not allow to normalise the memory performance of MCI patients since they still recalled fewer target words than healthy older adults. In addition, the ability to benefit from novelty to improve memory appears to be related to hippocampal volume