An anonymous reader quotes a report from The Guardian: A group of volunteers who took a trip in the name of science have helped researchers uncover how LSD messes with activity in the brain to induce an altered state of consciousness. Brain scans of individuals high on the drug revealed that the chemical allows parts of the cortex to become flooded with signals that are normally filtered out to prevent information overload. The drug allowed more information to flow from the thalamus, a kind of neural gatekeeper, to a region called the posterior cingulate cortex, and it stemmed the flow of information to another part known as the temporal cortex. This disruption in communication may underpin some of the wacky effects reported by LSD users, from feelings of bliss and being at one with the universe to hallucinations and what scientists in the field refer to as “ego dissolution,” where one’s sense of self disintegrates.
For the study, the researchers invited 25 healthy participants into the lab to be scanned under the influence of LSD and, on another occasion, after taking a placebo. They were shown around the scanner beforehand to ensure they felt comfortable going inside when the drug took hold. Had the machine suddenly taken on a threatening demeanor, the scans might not have come out so well. The scientists wanted to test a hypothesis first put forward more than a decade ago. It states LSD causes the thalamus to stop filtering information it relays to other parts of the brain. It is the breakdown of this filter that gives rise to the weird effects the drug induces, or so the thinking goes. Scans of the volunteers’ brains suggested there may be some truth to the hypothesis. On LSD, the thalamus let more information through to some parts of the brain and suppressed information bound for others. “What we found is that the model is mostly true, but how information is distributed to the cortex under LSD is much more specific than it predicts,” a researcher said. The latest research is published in Proceedings of the National Academy of Sciences.