"Only a handful of brain scans have been made of people with musical hallucinations. Dr. Tim Griffiths, a neurologist at the University of Newcastle Upon Tyne in England, performed one of these studies on six elderly patients who developed musical hallucinations after becoming partly deaf."
"Dr. Griffiths discovered a network of regions in the brain that became more active as the hallucinations became more intense. "What strikes me is that you see a very similar pattern in normal people who are listening to music," he said.
The main difference is that musical hallucinations don't activate the primary auditory cortex, the first stop for sound in the brain. When Dr. Griffith's subjects hallucinated, they used only the parts of the brain that are responsible for turning simple sounds into complex music."