A group of volunteers who traveled on behalf of science helped researchers to discover how LSD interferes with brain activity to induce an altered state of consciousness.
Brain scans of drug-rich individuals have revealed that the chemical allows parts of the cortex to be flooded with signals that are normally filtered to prevent information overload.
The drug allowed more information to flow from the thalamus, a type of neural porter, to a region called the posterior cingulate cortex, and this resulted in the flow of information to another part known as the temporal cortex.
This interruption in communication can support some of the crazy effects reported by LSD users, of feelings of happiness and being in harmony with the universe of hallucinations, and what scientists in the area call "ego dissolution," where the sense of self becomes disintegrates.
For the study, the researchers invited 25 healthy participants to be examined under the influence of LSD and, on another occasion, after taking a placebo. They were shown around the scanner in advance to make sure they felt comfortable entering when the drug caught. If the machine suddenly assumed a threatening behavior, the tests might not have worked out so well.
Scientists wanted to test a hypothesis first presented more than a decade ago. He claims that LSD causes the thalamus to stop filtering the information it transmits to other parts of the brain. It is the collapse of this filter that gives rise to the strange effects that the drug induces, or at least reasoning.
"The world around us is not the world we perceive, because the thalamus filters out what it considers to be irrelevant information," said Katrin Preller, a researcher at the University Hospital for Psychiatry in Zurich. "We do not necessarily perceive everything that exists, because that would be an overload of information."
Voluntary brain scans suggest that there may be some truth in the hypothesis. In LSD, the thalamus passed on more information to parts of the brain and suppressed information to others. "What we found is that the model is truer but as the information is distributed to the cortex under LSD it is much more specific than anticipated," Preller said.
It is unclear how tinkering with the flow of information in the brain gives rise to particular sensations linked to LSD, but there are some suggestions from previous work. It is believed that the posterior cingulate cortex, for example, plays a role in the formation of the sense of self, so overloading it can lead to feelings of self-disintegration.
LSD, or lysergic acid diethylamide, was first synthesized in 1938 and had a profound impact on psychology and psychiatric research during the 1950s and 1960s. Although its adoption as a recreational drug led to its ban, many scientists now suspect that it can be a powerful new weapon in the battle against depression and other mental disorders.
"We are getting closer to understanding the complexity of what happens to LSD in the brain and this is particularly important if we are to develop new drugs," Preller said. The latest research is published in the Proceedings of the National Academy of Sciences.
The work follows an important study in 2016 that found that under the influence of LSD, the brain recruited far more regions for visual processing than normal, enriching the images that people saw even when their eyes were closed. The research was the first to show how the brain looks like on LSD in a modern scanner.