Neural mechanisms of impaired postural control in people with Parkinson's disease

PROJECT SUMMARY Parkinson’s disease (PD) is a prominent neurodegenerative disease with over 90,000 cases being diagnosed annually. Little is known about the pathogenesis of abnormal trunk posturing/impaired postural control in PD. Trunk postural control is particularly problematic during both standing (e.g.

excessive forward and lateral flexion) and turning (“en bloc” turning). Corticospinal, reticulospinal and vestibulospinal systems contribute to the control of trunk muscles, but their roles in the pathogenesis of disordered trunk control are unclear. To date, no studies have investigated the function of descending

neural pathways on the control of the trunk during static postures and dynamic movements in people with PD. This proposal will use two noninvasive neuromodulation techniques, transcranial magnetic stimulation (TMS) and electrical vestibular stimulation (EVS), to characterize: (i) the excitability of

corticomotoneuronal (corticospinal and corticoreticulospinal) projections to trunk muscles during quasi-static postures and prior to turning, and (ii) the engagement of vestibulospinal projections during standing and turning. Aim 1: (A) Compare trunk muscle corticomotoneuronal and intracortical excitability (via TMS)

in sitting and standing between people with PD and healthy controls. (B) Examine the relationships between TMS responses and quantitative assessments of posture and gait. Trunk muscle responses to single and paired-pulse TMS of the primary motor cortex trunk region will quantify the excitability of corticomotoneuronal and intracortical (inhibition and facilitation) pathways in quasi-static postures (sitting

and standing). Aim 2: (A) Compare the modulation of corticomotoneuronal pathway excitability to trunk muscles (via TMS) immediately prior to turns in people with PD and healthy controls. Single pulse TMS will quantify the change in excitability of corticomotoneuronal pathways immediately prior to a 90° turn. Aim 3: Compare the modulation of (A) EVS-ground reaction force (GRF) coherence and (B)

EVS-trunk electromyograph (EMG) coherence prior to and during turns in people with PD and healthy controls. Vestibulo-postural coupling will be tested by computing the coherence between EVS and the (A) GRFs used to maintain balance and (B) surface EMG from the trunk muscles. This work will provide novel

insight into the pathophysiology of disordered trunk control in PD. This proposed study is part of a fellowship training plan that will include training in (i) quantitative motor assessments using biomechanical and EMG techniques, (ii) clinical neurophysiological and neuromodulation techniques, and (iii) professional

development skills that are essential for a successful career as a rehabilitation scientist. The University of Minnesota’s expansive research infrastructure, the multi-disciplinary Program in Rehabilitation Science, and the Movement Disorders Laboratory create an ideal environment for completing this research and training.