Functional neuroimaging and repetitive transcranial magnetic stimulation in Parkinson's disease

Functional neuroimaging provides insights into the pathogenesis of motor symptoms in Parkinson's disease (PD) and improves our understanding of both established neuromodulatory therapies such as deep brain stimulation (DBS) and potential ones such as repetitive transcranial magnetic stimulation (rTMS). Functional imaging studies can reveal the consequences of the dopaminergic lesion in PD among a widespread network of subcortical-cortical regions. Characteristic patterns of normal cortical brain activation for motor tasks are systematically altered in PD. Recent work has emphasized the task dependence of these changes and their gradual evolution over the course of the disease. Clinically relevant PD treatment with medications or DBS tends to normalize these patterns. In this context, rTMS is discussed as a potential noninvasive alternative for neuromodulation of cortical function. Although rTMS is not a current treatment, we review recent rTMS studies in PD that suggest its promise, illustrate how functional imaging can guide application of rTMS, and suggest that subcortical dopamine release could be an rTMS mechanism of action. The combination of rTMS and functional neuroimaging broadens our knowledge of functional cortical networks in PD, which can eventually provide physicians with pathophysiologic information about different PD treatment options and rationales for neuromodulatory interventions.