Objective:  To identify neural mechanisms relating to semantic fluency deficits in PD-MCI and to establish possible neuroimaging markers for Parkinson’s disease (PD) with dementia. 

Background: Patients with PD are found to experience a plethora of symptoms ranging from subtle cognitive complaints to severe cognitive dysfunction leading to dementia. The cognitive dysfunction detrimentally impacts patients’ quality of life and contribute to a high disease burden. Impairment in semantic fluency is reported to be associated with PD with mild cognitive impairment (PD-MCI) and is thought to be a risk factor for developing dementia in PD. Therefore, the aim of this study is to identify neural mechanisms relating to semantic fluency deficits in PD-MCI.

Methods: Sixteen non-demented PD patients and 6 age and gender-matched healthy controls (HC) participated. PD group was subdivided to the presence of MCI using a comprehensive cognitive battery according to the recommended diagnostic criteria (Litvan et al. 2012). Participants were scanned in 3T Siemens PRISMA using event-related fMRI to measure differences in semantic fluency between groups. The task was composed of rest, automated, category generation, and category switching. fMRI data was analysed using SPM12 and whole brain analysis. Significant was determined as p<0.001 uncorrected, with cluster level FWE correction (p<0.05).

Results: Ten PD patients were diagnosed with MCI with 1.5SD below norms. Behavioural data showed that an average number of items in all conditions were relatively smaller in PD-MCI compared to other groups. Using whole brain fMRI, the main effect of group for category generation highlighted right medial cingulate cortex, bilateral operculum including insular lobe, supramarginal gyrus, bilateral cerebellum and right precuneus. PD-MCI showed alteration in left temporal pole compared to PD-nMCI.

Conclusions: PD-MCI showed decreased activity in cerebellum compared to HC which may relate to its role of contributing in language processing. Also, there were differences in activation in the left temporal pole between PD-MCI and PD-nMCI. The left temporal pole deficits have been linked to semantic dementia. Our results demonstrate a possible involvement of this region with respect to impairment in semantic fluency in PD-MCI and potentially serve as a marker for dementia. This abstract is also submitted to OHBM 2017 Conference. 

References: Litvan, I., J. G. Goldman, A. I. Tröster, B. A. Schmand, D. Weintraub, R. C. Petersen, B. Mollenhauer, C. H. Adler, K. Marder, C. H. Williams‐Gray, D. Aarsland, J. Kulisevsky, M. C. Rodriguez‐Oroz, D. J. Burn, R. A. Barker and M. Emre (2012). ‘Diagnostic criteria for mild cognitive impairment in Parkinson’s disease: Movement Disorder Society Task Force guidelines.’ Movement Disorders, vol. 27, no. 3, pp. 349-356.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/understanding-neural-activation-in-semantic-fluency-in-parkinsons-disease-with-mild-cognitive-impairment/