Depression occurs frequently in patients suffering from Parkinson's disease (PD). However, the neural basis of depression in PD remains unclear. Diffusion magnetic resonance imaging (DMRI) connectometry is based on the spin distribution function (SDF), which quantifies the density of diffusing water.

The aim of this study was to assess the microstructural changes in the brain connectivity of PD patients with and without depressive symptoms.

DMRI was used to assess microstructural abnormalities in the brains of 16 PD patients with depressive symptoms compared to 11 PD patients without depressive symptoms. Data used in the preparation of this paper were obtained from the Parkinson's progression markers initiative (PPMI) database (data/). This dataset was acquired on a 3-Tesla scanner (Siemens), producing 64 DWI at b=1000s/mm² and one b0 image. Diffusion MRI data were corrected for subject motion, eddy current distortions, and susceptibility artefacts due to magnetic field inhomogeneity. DMRI connectometry was conducted in a total of 27 patients using percentage measurement.

PD Patients with depressive symptoms showed decreased anisotropy (FDR<0.05) in the fornix bilaterally, left inferior longitudinal fasciculus (ILF) and corticospinal tract bilaterally compared to PD patients without depressive symptoms.

Lesser WM integrity of the left ILF fibers, which connect visual face recognition areas to the amygdala and hippocampus, seems to be associated with depressive symptoms in PD patients. Our study supports the hypothesis that neurodegenerative processes in projections from the somatosensory, cingulate, and insular cortices may be related to depression in PD.