Objective: To evaluate the role of adult hippocampal neurogenesis (AHN)-associated memory measures to the cognitive performance of people with Parkinson’s disease (PwP) with or without cognitive impairment as a potential biomarkers.

Background: Episodic memory impairment is common in Parkinson’s disease (PD) and is associated with an increased risk of dementia^1,2. Dysfunction in AHN, the generation of new neurons in the subventricular zone of the dentate gyrus in the hippocampus, has been associated with episodic memory deficit, particularly in pattern separation and recognition memory³, and can be assessed with the Mnemonic Similarity Task (MST)⁴.

Method: Clinical and demographic data were collected from a cohort of PwP recruited at the Parkinson’s Foundation Centre of Excellence at King’s College Hospital, London, UK. Global cognitive performance was assessed using the Montreal Cognitive Assessment (MoCA) and a cut-off of <26 was used to define the presence of cognitive impairment. Subjective memory decline (SMD) was assessed by the score of the first memory item of the MDS-NMS scale⁵.  In the testing phase of the MST task, participants decided whether visualised images were “old”, “similar” or “new”, compared to images previously shown during an encoding phase. A verbal measure of episodic memory, the Hopkins Verbal Learning Test-Revised (HVLT-R), was also assessed.

Results: Among 18 PwP, six were defined as cognitively impaired (CI) and 12 as cognitively unimpaired (CU). Significant differences between the two groups were observed in the Delayed Recall and Retention scores of HVLT-R (p<0.001), while no significant differences in MST outcomes were detected (Table). However, in the CI group, a significant positive correlation was found between the recognition score of the MST and the HVLT-R recognition discrimination index (rho=0.845, p=0.034), while a significant negative correlation was observed in the CU group between the lure discrimination index of the MST and the SMD score (rho=-0.606, p=0.037).

Conclusion: In this exploratory study, we observed an association between visual and verbal recognition memory in PwP with cognitive impairment. On the other hand, pattern recognition memory correlated with a measure of SMD in CU subjects. These preliminary findings suggest that AHN-associated memory outcomes may signpost different stages of memory dysfunction in PwP.

References: [1] Aarsland D, Batzu L, Halliday GM, Geurtsen GJ, Ballard C, Ray Chaudhuri K, Weintraub D. Parkinson disease-associated cognitive impairment. Nat Rev Dis Primers. 2021 Jul 1;7(1):47. doi: 10.1038/s41572-021-00280-3. Erratum in: Nat Rev Dis Primers. 2021 Jul 13;7(1):53. PMID: 34210995.
[2] Das T, Hwang JJ, Poston KL. Episodic recognition memory and the hippocampus in Parkinson’s disease: A review. Cortex. 2019 Apr;113:191-209. doi: 10.1016/j.cortex.2018.11.021. Epub 2018 Dec 4. PMID: 30660957; PMCID: PMC6445686.
[3] Kim C, Pinto AM, Bordoli C, Buckner LP, Kaplan PC, Del Arenal IM, Jeffcock EJ, Hall WL, Thuret S. Energy Restriction Enhances Adult Hippocampal Neurogenesis-Associated Memory after Four Weeks in an Adult Human Population with Central Obesity; a Randomized Controlled Trial. Nutrients. 2020 Feb 28;12(3):638. doi: 10.3390/nu12030638. PMID: 32121111; PMCID: PMC7146388.
[4] Stark SM, Yassa MA, Lacy JW, Stark CE. A task to assess behavioral pattern separation (BPS) in humans: Data from healthy aging and mild cognitive impairment. Neuropsychologia. 2013 Oct;51(12):2442-9. doi: 10.1016/j.neuropsychologia.2012.12.014. Epub 2013 Jan 9. PMID: 23313292; PMCID: PMC3675184.
[5] Chaudhuri KR, Schrag A, Weintraub D, Rizos A, Rodriguez-Blazquez C, Mamikonyan E, Martinez-Martin P. The movement disorder society nonmotor rating scale: Initial validation study. Mov Disord. 2020 Jan;35(1):116-133. doi: 10.1002/mds.27862. Epub 2019 Sep 30. Erratum in: Mov Disord. 2020 Oct;35(10):1892. PMID: 31571279; PMCID: PMC7037759.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/adult-hippocampal-neurogenesis-associated-memory-performance-in-people-with-parkinsons-disease-with-and-without-cognitive-impairment/