["Little is known whether and how chronic exposure to dopaminergic treatment alters physiological mechanisms in Parkinson's disease (PD).", 'Two clinically similar groups of PD patients, one consisting of drug-naïve patients and another of patients already on chronic dopaminergic medication (when off medication), were compared to each other and to a control group. Plasticity and excitability of the hand primary motor cortex of the more affected side were evaluated using transcranial magnetic stimulation (TMS) techniques.', 'There was little difference between two patient groups, and both groups showed similar differences in comparison to controls: decreased facilitatory sensory-motor plasticity (as measured by paired associative stimulation [PAS] protocol), impaired short-interval intracortical inhibition (SICI), and diminished slope of input-output curves at higher TMS intensities. The exception was that 30 min after PAS, intracortical facilitation (ICF) was significantly reduced in drug-naïve patients, whereas it changed much less in other two groups.'] Does history of exposure to dopaminergic medication affect motor cortex plasticity and excitability in Parkinson 's disease?