This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'Stimulation of which of the following areas of brain is experimentally used to control intractable pain \nSelect and explain. \nA. Periaqueductal grey matter, B. Mesencephalon, C. Subthalmic nucleus, D. Medical fore brain bundle', 'role': 'user'}, {'content': "Answer: A \nExplanation: ganong's review of medical physiology 24th edition . *mesencephalic periaqueductal gray(PAG) is pa of descending pathway that modulates pain transmission by inhibition of primary afferent transmissiion in the dorsal horn of spinalcord *PAG neurons project directly to and activate two groups of neurons in brainstem:neurons in nucleus raphe magnus and in rostral ventromedial medulla . *neurons from both region project to dorsal horn and inhibit dorsal horn neuron activity.", 'role': 'assistant'}]