A group of volunteers traveling on behalf of science has helped researchers uncover how LSD affects brain activity to bring about an altered state of consciousness. The chemical allows signals to flood parts of the cortex, which are usually filtered out to prevent information overload.
The drug drew more information from the thalamus, a sort of neural gatekeeper, into a region called the posterior cinched cortex, and it obstructed the flow of information to another part known as the temporal cortex.
This interruption of communication can underpin some of the crazy effects reported by LSD users, from happiness to the universe to hallucinations and whatever scientists in the field are talking about "ego dissolution" in which the Self-esteem disintegrates.
For the study, the researchers invited 25 healthy participants to the world to be sampled under the influence of LSD and on another occasion after taking a placebo. They were previously led around the scanner to make sure they were comfortable with the drug. If the machine had suddenly assumed a threatening behavior, the scans might not have worked so well.
The scientists wanted to test a hypothesis that was set up more than ten years ago. It says that LSD causes the thalamus to stop filtering information that it passes on to other parts of the brain. It is the breakdown of this filter that leads to the strange effects that the drug triggers, or so is the thinking.
"The world around us is not the world we perceive because the thalamus filters out what is considered to be irrelevant information," says Katrin Preller, researcher at the project of the University Department of Psychiatry in Zurich. "We do not necessarily perceive everything that is there because that would be an overload of information."
Scans of volunteers' brains suggested that the hypothesis may be true. In LSD, the thalamus transmitted more information to some parts of the brain and suppressed information for others. "We found that the model is mostly correct, but the distribution of information to the cortex under LSD is much more specific than it predicts," Preller said.
It is unclear how the confusion with the flow of information in the brain causes particular feelings related to LSD, but there is some evidence from previous work. For example, it is believed that the posterior cingulated cortex plays a role in shaping one's own sense of self, so overloading can provoke a sense of self-destruction.
LSD or lysergic acid diethylamide was first synthesized in 1938 and had a profound impact on psychology and psychiatric research in the 1950s and 1960s. While its adoption as a recreational drug has led to a ban, many scientists now believe that this can be a powerful new weapon in the fight against depression and other mental disorders.
"We come closer to the complexity of what happens to LSD in the brain and this is especially important when we want to develop new drugs," Preller said. The latest research has been published in Proceedings of the National Academy of Sciences.
The work follows a large study from 2016, which found that the brain under the influence of LSD recruited many more regions for visual processing than normal and enriched the image population even when their eyes were closed. Research showed for the first time what the brain of a modern scanner looks like on LSD.