Intensive breathing exercises can reduce blood flow to the brain by up to 45% and alter communication between brain networks, according to a new brain-imaging study. Participants reported experiences resembling some effects of psychedelic drugs, including altered perception, vivid mental imagery, a sense of unity and changes in self-experience. The researchers, presenting the work at the ECNP Congress in Munich, say changes in brain communication, rather than reduced blood flow alone, appear to be key to the altered state.