Resting-state hippocampal asymmetry as a marker for memory and olfactory deficit in parkinson’s disease

Memory decline is a central cognitive symptom in Parkinson's Disease (PD). While task-fMRI studies link hippocampal activity (AHA) to poorer memory and olfactory performance, this relationship during rest remains understudied. The objectives of this study are to examine differences in resting-state hippocampal networks, explore the occurrence of reduced AHA within these networks, and investigate its impact on memory and olfaction in PD. Thirty-nine PD patients awaiting evaluation for device-aided Parkinson therapy and 46 healthy controls (HC) underwent resting-state fMRI (rs-fMRI). PD patients also completed a memory and olfactory assessment. Co-activation pattern (CAP) analysis was performed on the rs-fMRI data. Our results demonstrated reduced activity in two hippocampal networks in PD: Network 1, incorporating the visual cortex, cerebellum, superior parietal lobule, and precuneus, and Network 5, incorporating parts of the central executive network. PD subgroups with reduced AHA in Network 1 and 5 performed significantly worse on tests of auditory-verbal short-term, long-term and recognition memory, as well as odor identification. In conclusion, within specific resting-state hippocampal networks, reduced AHA in PD is linked to poorer auditory-verbal memory and odor identification.