FTA:

New research shows that our brain displays a similar pattern of activity during dreams as it does during a mind-expanding drug trip. […] “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. 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.”

[…] The mind tips into a more chaotic regime where there are more networks available than normal. […] Collectively, the present results suggest that psilocybin can manipulate this critical operating point.