Objective: Objectives: (1) Measure test re-test reliability of dual-coil transcranial magnetic stimulation (TMS) measures of supplementary motor area-primary motor cortex connectivity (SMA-M1 connectivity). (2) Investigate whether SMA-M1 connectivity is associated with tremor severity in people with tremor-dominant Parkinson’s disease (PD).

Background: Background: The pathophysiology of tremor-dominant PD remains poorly understood. Many people with tremor-dominant PD are resistant to the gold-standard dopaminergic replacement therapy. With PD comes changes in motor brain regions, including a decrease in SMA activity [1]. SMA has strong excitatory connections to M1, which can be measured using dual-coil TMS, and SMA-M1 connectivity is associated with motor control [2, 3]. The aims of the current study were to (1) measure test-retest reliability of dual-coil TMS measures of SMA-M1 connectivity in adults without PD, and (2) examine whether SMA-M1 connectivity is altered in people with tremor-dominant PD compared to age- and gender-matched controls, and whether the magnitude of SMA-M1 connectivity is associated with tremor severity in people with PD.

Method: Methods: SMA-M1 connectivity was measured in two sessions separated by ~7 days in younger and older adults without PD (N = 60). SMA-M1 connectivity and tremor were measured in people with tremor-dominant PD OFF medication in a single session.

Results: Results: In younger and older adults without PD, results showed good test re-test reliability of SMA-M1 connectivity in younger (r = .711) and older (r = .528) adults. There was no significant difference in SMA-M1 connectivity between younger and older adults. Based on preliminary results, we hypothesise that people with PD will have reduced SMA-M1 connectivity when compared to age- and gender-matched controls, and the magnitude of SMA-M1 connectivity will be negatively associated with tremor severity in tremor-dominant PD.

Conclusion: Conclusion: The current findings suggests that SMA-M1 connectivity can be reliably measured using dual-coil TMS. This has important implications for the use of dual-coil TMS to investigate SMA-M1 connectivity in tremor-dominant PD, as well as other movement disorders, which will help inform clinical practice.

References: References: 1. Pan, P.L., et al., Abnormalities of regional brain function in Parkinson’s disease: a meta-analysis of resting state functional magnetic resonance imaging studies. Scientific Reports, 2017. 7: 10. 2. Nachev, P., C. Kennard, and M. Husain, Functional role of the supplementary and pre-supplementary motor areas. Nature Reviews Neuroscience, 2008. 9(11): 856-869. 3. Green, P.E., et al., Supplementary motor area-primary motor cortex facilitation in younger but not older adults. Neurobiology of Aging, 2018. 64: 85-91.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/examining-supplementary-motor-area-primary-motor-cortex-connectivity-in-tremor-dominant-parkinsons-disease-using-a-novel-transcranial-magnetic-stimulation-protocol-to-inform-clinical-practice/