This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Pa of Basal ganglia, primarily involved in parkinsonism? \nSelect and explain. \nA. Subthalamic nudes, B. Substantia nigra, C. Globus pallidus, D. None', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Substantia nigra", 'role': 'assistant'}]