They found that with psilocybin, activity in the more primitive brain network linked to emotional thinking became more pronounced, with several parts of the network - such as the hippocampus and anterior cingulate cortex - active at the same time. This pattern is similar to when people are dreaming.
They also found that volunteers on psilocybin had more disjointed and uncoordinated activity in the brain network that is linked to high-level thinking, including self-consciousness.
"People often describe taking psilocybin as producing a dreamlike state and our findings have, for the first time, provided a physical representation for the experience in the brain," said Robin Carhart-Harris of Imperial College London's department of medicine, who also worked on the study.
"I was fascinated to see similarities between the pattern of brain activity in a psychedelic state and the pattern of brain activity during dream sleep, especially as both involve the primitive areas of the brain linked to emotions and memory."