Dissertation Defence: From Motor Unit Behaviour to Functional Ability: The Role of Dopaminergic Medication in Parkinson’s Disease

Parisa Alaei, supervised by Dr. Jennifer Jakobi, will defend their dissertation titled “From Motor Unit Behaviour to Functional Ability: The Role of Dopaminergic Medication in Parkinson’s Disease” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Kinesiology.

An abstract for Parisa Alaei’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.

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ABSTRACT

The overall aim of this dissertation is to evaluate the influence of dopaminergic medication on the affected upper limb in people with Parkinson’s disease (PD), spanning outcomes from functional performance, such as hand dexterity, to underlying neuromuscular mechanisms at the motor unit (MU) level. To achieve this goal, 16 people with PD and 13 control group participated in this study. Participants with PD completed two identical sessions in a randomized order: one in the ON medication phase and one in the OFF medication phase. The control group completed only one session. The specific objectives of this dissertation were as follows: 1) To compare the treated (ON) and untreated (OFF) phases in people with PD to examine effects of dopaminergic medication on hand dexterity, motor symptom severity, twitch contractile properties and maximal voluntary contraction, 2) To determine whether dopaminergic medication optimizes motor neuronal properties and force control during an isometric contraction in the more affected upper limb of people with PD, 3) To investigate motoneuron excitability in people with PD during ON and OFF medication phases and to compare them with age-matched controls. Study #1 addressed objective 1 by demonstrating that dopaminergic treatment improved motor symptoms, hand dexterity, and strength, without altering electrically induced contractile properties. Improved hand dexterity during treatment appears to be linked to strength gains independent of peripheral muscle changes. Study #2 addressed objective 2 by showing that dopaminergic medication enhances force control in people with PD by improving force steadiness and reducing MU discharge variability, particularly during the least steady period of a contraction. Also, findings suggest that medication may also reduce unwanted muscle coactivation and increase MU recruitment threshold. Finally Study #3 addressed objective 3 by revealing that motoneuron excitability altered in people with PD compared with age-matched controls, independent of dopaminergic medication. These changes, likely driven by increased calcium influx, reduced synaptic inhibition, and heightened cortical facilitation and are not substantially normalized by dopamine therapy. Overall, this dissertation provides new insight into the effects of dopaminergic medication on MU characteristics in people with PD, highlighting its importance for improving force control and functional outcomes.