A 62-year-old man from Delhi presents with a 3-year history of progressive tremor at rest, rigidity, and bradykinesia. Examination reveals a resting tremor that disappears with intentional movement, cogwheel rigidity in the upper limbs, and difficulty initiating gait. MRI brain is normal. Based on the clinical presentation consistent with Parkinson disease and the anatomical dysfunction of the basal ganglia circuits, what is the most appropriate next step in management?