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The influence of contextual constraint on verbal selection mechanisms and its neural correlates in Parkinson’s disease

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Abstract

A small number of studies have described verbal selection deficits in Parkinson’s disease (PD) when selection must occur among competing alternatives. However, these studies have largely focused on single-word processing, or have utilised sentence stems that carry high contextual constraint, thus reducing selection demands. The present study aimed to determine the influence of variable contextual constraint on the selection of a verbal response in PD. This was achieved using an adaption of the Hayling Sentence Completion Task whereby PD participants and matched controls were required to provide a single word to complete a cloze probability sentence stem that carried a low, medium, or high degree of contextual constraint. Results revealed no main effect of group in terms of response time or accuracy, though a group-by-condition interaction in accuracy was noted. This was characterised by a significant difference in accuracy between low and medium levels of constraint for control participants, but no significant difference for the PD group. Functional MRI data revealed marked between-group differences in underlying neural activity. The control group showed increased recruitment of the dorsal striatum and the vlPFC under conditions that placed greater demands upon selection (i.e. low and medium constraint), and greater activity overall in the left dlPFC and right vlPFC. However, in the PD group, behavioural performance appeared to be maintained despite underlying decreases in frontostriatal activity, suggesting other compensatory mechanisms that may include changes in functional connectivity or an over-medication effect in frontal networks in response to loss of signalling in cortico-subcortical pathways.

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Acknowledgements

The authors thank K. O’Brien, M. West, A. Rawlings, and N. Bell for their assistance with data collection and/or scoring, and J. Yang for her assistance with the pre-processing of fMRI data. Declarations of interest: none.

Funding

This study was funded by the Australian Research Council [grant number DP120104420]. M. Isaacs was supported by an Australian Government Research Training Program Scholarship and the Asia-Pacific Centre for Neuromodulation. D. Copland was supported by University of Queensland Vice Chancellor’s Fellowship and ARC Future Fellowship.

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Correspondence to Megan L. Isaacs.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Isaacs, M.L., McMahon, K.L., Angwin, A.J. et al. The influence of contextual constraint on verbal selection mechanisms and its neural correlates in Parkinson’s disease. Brain Imaging and Behavior 15, 865–881 (2021). https://doi.org/10.1007/s11682-020-00296-5

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