Functional remapping in networks of the Parkinsonian brain: A preclinical neuroimaging perspective with clinical correlates.

Parkinson's disease (PD) is increasingly understood as a neurodegenerative condition whose pathology extends beyond the direct and indirect basal ganglia pathways. Clinically, patients are all too painfully aware of dysfunction not only of motor circuits but also of somatosensory, autonomic, cognitive, and emotional systems. Functional neuroimaging studies have begun to document a functional reorganization in the PD brain across a wide number of networks. In particular, the cerebellar-thalamocortical, as well as the fronto-striatal circuit, have been shown to undergo functional reorganization. In this narrative review, citing preclinical as well as clinical neuroimaging studies, our objective is to highlight trends and discuss the relevance of cerebral adaptive changes. It remains clear that not all changes contribute to the normalization of functions. Parsing differences between functional "compensation," "silencing," or "maladaptation" in neural circuits is important. A necessary next step in neurorehabilitation is the question of whether compensatory cerebral changes can be enhanced. In this regard, physical exercise remains of interest, given that in patients, exercise may allow some degree of symptom improvement and possibly slow the course of the disease. Future interventions may wish to integrate neuroimaging findings as potential targets to support neuroplastic changes.