Tai, Y. F. | Search bioRxiv

bioRxiv2024

Anatomical Abnormalities Suggest a Compensatory Role of the Cerebellum in Early Parkinson's Disease

Brain atrophy is detected in early Parkinsons disease (PD) and accelerates over the first few years post-diagnosis. This was captured by multiple cross-sectional studies and a few longitudinal studies in early PD. Yet only a longitudinal study with a control group can capture accelerated atrophy in early PD and differentiate it from healthy ageing. Accordingly, we performed a multicohort longitudinal analysis between PD and healthy ageing, examining subcortical regions implicated in PD pathology, including the basal ganglia, thalamus, corpus callosum (CC), and cerebellum. Longitudinal volumetric analysis was performed on 56 early PD patients and 53 matched controls, with scans collected 2-3 years apart. At baseline, the PD group showed a greater volume in the pallidum, thalamus, and cerebellar white matter (WM), suggesting potential compensatory mechanisms in prodromal and early PD. After 2-3 years, accelerated atrophy in PD was observed in the putamen and cerebellar WM. Interestingly, healthy controls - but not PD patients - demonstrated a significant decline in Total Intracranial Volume (TIV), and atrophy in the thalamus and mid-CC. Between-group analysis revealed more severe atrophy in the right striatum and cerebellar WM in PD, and in the mid-posterior CC in controls. Using CEREbellum Segmentation (CERES) for lobule segmentation on the longitudinal PD cohort, we found a significant decline in the WM of non-motor regions in the cerebellum, specifically Crus I and lobule IX. Our results highlight an initial increase in cerebellar WM volume during prodromal PD, followed by significant degeneration over the first few years post-diagnosis.

neuroscience↗

bioRxiv2023

Modulatory Effect of Levodopa on the Basal Ganglia-Cerebellum Connectivity in Parkinson's Disease

Levodopa has remained the mainstay of medical therapy for Parkinsons disease since its development in the 1980s. However, long-term medication use is associated with declining clinical efficacy and the emergence of motor complications. Unveiling the effects of levodopa on brain functional reorganisation at a relatively early treatment phase is therefore imperative to inform the optimisation of Parkinsons therapeutics. In this study, we comprehensively investigated levodopas modulation on the resting-state functional connectivity in the cortico- basal ganglia-cerebellum system at regional and network levels, with dual cross-sectional and longitudinal designs. The data was extracted from the Parkinsons Progression Marker Initiative (PPMI) dataset. The cross-sectional patient groups comprised 17 Parkinsons patients on stable levodopa medication and 15 drug-naive patients, while the longitudinal set included 14 Parkinsons patients measured at both drug-naive and levodopa-medicated conditions. With nodes defined across cortical, basal ganglia, and cerebellar networks, we conducted univariate comparisons of the internodal connectivity strength between the medication conditions using nonparametric permutation. At the network level, we computed multivariate combinations of individual connections within and between the networks, followed by an assessment of their discriminative capabilities on patients medication classes using supervised machine learning. The univariate seed-based approach showed no statistically significant effect of levodopa in either dataset. However, the network connectivity pattern between basal ganglia and the cerebellum displayed a robust classification power in the longitudinal dataset and a similar trend was observed in the cross-sectional. The role of the cerebellum is often overlooked in previous functional integration investigations of Parkinsons disease and levodopa effects. Considering the recent evidence suggesting the bidirectional communications between the cerebellum and basal ganglia networks, our study provides further insight into the importance of inter-network functional connectivity in Parkinsons, as well as in the functional and plastic processes following levodopa medication.

neuroscience↗