Physiological changes in advanced Parkinson's disease: Altered motor cortical plasticity and its significance in pathophysiology and clinical symptoms

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by dopaminergic neurodegeneration in the substantia nigra. Dopamine plays an important role in the induction of synaptic plasticity, and plastic changes in the brain have been broadly investigated in PD. In humans, non‐invasive transcranial magnetic stimulation (TMS) has been widely used for plasticity induction in the motor cortex. In this review, we will discuss how dopamine receptors are involved in the induction of neuroplasticity, changes in corticostriatal plasticity in PD model animals, effects of dopamine on motor cortical plasticity in healthy humans, changes in motor cortical plasticity in PD patients including its relationship to motor symptoms, and, finally, altered plasticity in levodopa‐induced dyskinesia.