Reorganisation of diffusion microstructure in the precuneus is associated with preserved cognitive function in Parkinson’s disease

Functional neuroimaging studies of patients with Parkinson’s disease (PD) have repeatedly identified over-activations in midline structures (medial prefrontal cortex, anterior cingulate cortex, posterior cingulate cortex, and precuneus), especially in those without comorbid dementia. Here, we investigated whether the different cognitive profiles in PD were linked to measures of diffusion microstructure in medial regions of the brain. Using magnetic resonance based diffusion weighted imaging (DWI) in healthy volunteers (HV) and PD patients with and without mild cognitive impairment (PD-nonMCI and PD-MCI), applying diffusion tensor imaging (DTI) and high angular resolution diffusion imaging (HARDI) techniques, we observed: 1) increased fractional anisotropy (FA) in the precuneus and the anterior cingulate in the PD-nonMCI participants compared with the HV; 2) an association between precuneus FA and executive and memory function, respectively, in PD and HV; 3) a negative correlation between age and midline structure FA in PD but not HV; and 4) a differential association between cognitive scores and apparent fiber density (AFD) of the posterior cingulate-precuneus bundle in HV vs. PD. Together, these findings suggest that white matter reorganization of the posterior medial microstructures might serve a compensatory role for damaged basal ganglia function in PD-nonMCI.