Objective: Characterization of neural mechanisms of associative memory deficits in Parkinson’s disease (PD) without dementia (PD-non-Dementia).

Background: The early presence of memory deficits in PD might be a predictor of dementia. Yet, the neural origins of memory, and particularly associative memory deficits in PD are not well known. Associative memory is a form of episodic long-term memory that is highly resource-demanding compared to single item memory.

Methods: 23 healthy controls (HC), 29 PD-non-Dementia were studied (all≥60 years). Cognitive status was determined by a comprehensive neuropsychological assessment, and both normal and mild cognitive impairment patients consisted of PD-non-Dementia. Two encoding and two retrieval sessions of a face-scene pair associative memory test were performed in a 3 T MRI scanner, while BOLD (blood oxygen level dependent) fMRI (functional magnetic resonance imaging) T2* weighted images of the brain were acquired. Only correct retrieval answers were analyzed by FSL 5.0 using general linear model, z=2.3 threshold was applied, and p≤0.05 was considered significant. Three trial types familiar pair (hit), rearranged familiar pair (familiar lure), and never seen pair (control lure) were contrasted for characterizing neuronal mechanism between these two groups.

Results: Reduced activation of regular retrieval network (inferior frontal gyrus, precentral gyrus, post central gyrus, inferior parietal lobule) was observed in PD-non-Dementia compared to HC while correctly rejecting familiar lure over control lure. PD-non-Dementia showed reduced activation compared to HC in primary motor and sensory regions while correctly rejecting familiar lure over hit. PD-non-Dementia showed reduced activation compared to HC in inferior frontal gyrus and post central gyrus while correctly confirming hit over control lure.

Conclusions: Overall, reduced activation of default regions for associative memory (inferior frontal gyrus, precentral gyrus, post central gyrus, inferior parietal lobule) was observed in PD-non-Dementia for familiar pair (hit) and familiar lure over control lure, with more regions affected for familiar lure. Never seen pair (control lure) is just rejection, whereas rearranged familiar pair (familiar lure) is a more taxing associative memory for neuronal networks in PD compared to familiar pair.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/brain-mechanisms-of-associative-memory-deficits-in-parkinsons-disease-without-dementia/