Thalamic functional connectivity on 7-Tesla magnetic resonance imaging and its relation to motor signs in early-stage Parkinson's disease.

Background: It is well known that dysfunction of thalamocortical circuity generates the motor signs that lead to distinct disease processes and prognoses in Parkinson's disease (PD). This study aimed to leverage ultrahigh-field magnetic resonance imaging (MRI) to identify the connectivity alterations of thalamocortical circuity and clarify their relation to motor signs in early PD.

Methods: Patients with early-stage PD (n=55) and healthy controls (HCs, n=56) were recruited from March 2022 to July 2023. All participants underwent 7-Tesla MRI scans as the baseline. Sign scores were calculated from the Movement Disorder Society Unified Parkinson's Disease Rating Scale III. Significant differences in the functional connectivity between the thalamus subregions and cortex between the PD and HC groups were discovered. The association between altered thalamic functional connectivity and sign scores was evaluated using Spearman or Pearson correlation analysis with false discovery rate (FDR) correction.

Results: Compared to the HCs, the patients with early-stage PD exhibited a decreased functional connectivity between thalamic subregions (primary motor, sensory, occipital, premotor, and parietal thalamus regions) and the cortex [voxel-level P<0.001, cluster-level P_{family-wise error (FWE)} <0.05]. Further exploration of the connection pattern within thalamic subregions showed that the connection strength between the primary motor and sensory (t=2.055; P=0.042), sensory and occipital (t=2.173; P=0.032), and occipital and parietal (t=2.365; P=0.020) regions were reduced. Importantly, motor signs in early-stage PD were associated with the alterations of functional connectivity pattern between the parietal thalamus and left dorsolateral part of the superior frontal gyrus (r=-0.272; P_FDR =0.049) and the right thalamus (r=-0.267; P_FDR =0.048) .

Conclusions: These findings support the use of ultrahigh-field MRI for examining the thalamic subregions and clarifying their involvement in the neural mechanisms of various motor signs in early-stage PD.