Psychedelic drugs alter consciousness in a profound and novel way that increases the breadth and fluency of cognition. However, until recently, we were unable to offer an explanation for how the brain was altered to account for these effects.

In a new study, published in Human Brain Mapping, we scanned the brains of volunteers who had been injected with psilocybin – the chemical found in magic mushrooms which gives a psychedelic experience – and a control group who hadn't, and discovered two key things: that psilocybin increased the amplitude (or "volume") of activity in regions of the brain that are reliably activated during dream sleep and form part of the brain's ancient emotion system; and that psychedelics facilitate a state of "expanded" consciousness – meaning that the breath of associations made by the brain and the ease by which they are visited is enhanced under the drugs.