The default mode network integrity in patients with Parkinson's disease is levodopa equivalent dose-dependent

Disturbances in the default mode network (DMN) have been described in many neurological and psychiatric disorders including Parkinson's disease (PD). The DMN is characterized by basal activity that increases during rest or passive visual fixation and decreases ("deactivates") during cognitive tasks. The network is believed to be involved in cognitive processes. We examined the DMN in PD patients on dopaminergic medication with normal cognitive performance compared to age- and gender-matched healthy controls (HC) using fMRI and three methodological procedures: independent component analysis of resting-state data, analysis of deactivation during a complex visual scene-encoding task, and seed-based functional connectivity analysis. In the PD group, we also studied the effect of dopaminergic medication on the DMN integrity. We did not find any difference between the PD and HC groups in the DMN, but using the daily levodopa equivalent dose as a covariate, we observed an enhanced functional connectivity of the DMN in the posterior cingulate cortex and decreased activation in the left parahippocampal gyrus during the cognitive task. We conclude that dopaminergic therapy has a specific effect on both the DMN integrity and task-related brain activations in cognitively unimpaired PD patients, and these effects seem to be dose-dependent.