The neuromuscular control of gait with ageing and Parkinson's disease and the potential of transcranial direct current stimulation as intervention

Abstract

Gait disturbances amongst older adult (OA) and Parkinson’s disease (PD) populations often debilitate quality of life. Mobility decline is further exacerbated during activities of daily living involving dual-task walking; scanning the environment, adapting to fluctuations in terrain, and maintaining awareness of potential danger for safe ambulation. Current therapeutics are suboptimal, and more effective management is hindered by limited understanding of the underlying neuromuscular control of gait. Therefore, this thesis aims to investigate neural and muscular mechanisms underpinning gait control, as well as the effect of an emerging form of intervention, transcranial direct current stimulation (tDCS), to target gait impairment. In two studies, young adults (YA) (n=38), OA (n=36) and individuals with PD (n=30) were recruited. In Study I, all groups completed quantitative assessments of cognitive and motor cortical activity, distal lower limb muscle activity, spatiotemporal gait characteristics, clinical scores and neuropsychological measures, under single-task and dual-task walking conditions. In Study II, the effect of active anodal-tDCS on these measures was assessed (excluding lower limb activity) in YA and OA. Linear mixed effects models identified changes within groups and walking conditions, whilst correlations determined associations between the cortex, muscle and functional measures. Original contributions to knowledge describe a distinction in lower limb muscle and cortical activation strategies between ageing and PD groups during cognitively demanding walking. Lower limb muscle activity reveals discrete, sub-phase specific changes across the gait cycle discerning PD-pathology and holds potential as a biomarker to monitor disease progression. With ageing, greater cortical recruitment of both cognitive and motor areas may improve locomotor control. First evidence of quantifiable changes in cortical activity in an ageing group following tDCS intervention is also reported, although effect on gait performance remains unclear. This thesis enhances understanding of neuromuscular control underpinning gait deficits across ageing and PD and provides more refined targets to optimise intervention.