What exactly happens in a brain when it is hit by a hallucinogen? Lots of drugs have effects that are obvious extensions of our normal body processes; they raise moods, dull pain, or boost our energy. But hallucinogens are notable for giving their users experiences that are anything but normal.

Now, a team of Swiss researchers have used MRI imaging to follow the brain as it’s under the influence of acid. And their results support the idea that hallucinogens cause the breakdown of the system that helps the brain keep track of which information is coming from the real world and which is generated by the brain itself.

Cortex overload

The brain receives a steady flow of information, some from the outside world, some from the body, and some generated by its internal thought processes. Your brain has to essentially decide which of it to take seriously and raise to the level of consciousness, which to monitor subconsciously, and which to discard. Hallucinations, whether due to drugs or mental disorders, appear to involve a breakdown in this information processing.