Associating White Matter Microstructural Integrity and Improvements in Reactive Stepping in People with Parkinson’s Disease

Reactive steps are rapid responses after balance challenges. People with Parkinson's Disease demonstrate impaired reactive stepping, increasing fall risk. Although PwPD can improve steps through practice, the neural mechanisms contributing to improved reactive stepping in people with PD are poorly understood. This study investigated white-matter correlates of responsiveness to reactive step training in people with PD. Participants completed an eighteen-week multiple-baseline study consisting of two baseline assessments (B1 and B2) before training, a two-week, six-session training protocol, and two post-training assessments (immediate; P1) and two months after training (P2). Each assessment consisted of 3 backward reactive step trials. Outcomes included the anterior-posterior margin of stability, step length, and step latency. Tract-Based Spatial Statistics were performed to correlate white-matter microstructural integrity (fractional anisotropy and radial diffusivity) with retained improvements in reactive stepping at the two-month follow-up (P2–B2). Complete datasets were available from 22 participants. Greater retention of step length was associated with increased fractional anisotropy (better white-matter integrity) within the left anterior corona radiata (r = 0.54, p < 0.01), left posterior thalamic radiation (r = 0.54, p < 0.01), and right (r = 0.43, p = 0.04) and left (r = 0.0.40, p = 0.06) superior longitudinal fasciculi. Greater retention of step latency improvements was associated with lower radial diffusivity (greater white-matter integrity) within the left posterior (r = 0.60, p < 0.01) and anterior corona radiata (r = 0.61, p < 0.01). These findings highlight the importance of white-matter microstructural integrity in motor learning and retention processes in PD and may inform the development of targeted interventions to improve balance in people with PD.