Investigating Subtype-Specific Neuroplastic Changes Through White Matter Tractography in Parkinson's Disease

Introduction
Parkinson’s disease (PD) presents heterogeneous motor deficits associated with disruptions in distinct neural circuits. White-matter plasticity can be examined using diffusion tensor imaging (DTI) and fractional anisotropy (FA). Rhythmic Auditory Stimulation (RAS) induces compensatory plasticity within the basal ganglia-thalamo-cortical (BGTC) and cerebello-thalamo-cortical (CTC) networks, which are differentially preserved in rigidity-dominant (RD) and tremor-dominant (TD) PD, respectively. However, tract-specific plasticity underlying these effects remains poorly understood. This study examined FA differences in the internal capsule (IC), cerebellar projections, and corpus callosum (CC) to characterize subtype-specific neuroplasticity relevant to Neurologic Music Therapy (NMT).

Methods
Seventeen PD patients were classified as TD (n=11) or RD (n=6) using UPDRS scores. DTI data were processed in FSL and analyzed using tract-based spatial statistics. FA differences were assessed in predefined white-matter tracts. Principal component analysis (PCA) examined cerebellar peduncle (CP) organization.

Results
RD patients showed significantly higher FA in the left IC and across all CC subregions compared to TD patients. No group differences were observed in cerebellar projections. PCA revealed a unilateral left superior CP contribution in RD, whereas TD patients showed distributed bilateral contributions across all CPs.

Discussion
Findings suggest localized motor tract alterations and stronger interhemispheric connectivity in RD, contrasted with preserved, distributed cerebellar organization in TD. These subtype-specific patterns have implications for tailoring NMT interventions, with RD potentially benefiting from bilateral and cognitive–motor strategies and TD from cerebellar-based motor sequencing approaches.