LSD allows more information to flood into the brain by altering activity in the thalamus

New neuroimaging research provides evidence that the psychedelic drug LSD alters the capacity of the thalamus to control the flow of sensory information to other areas of the brain.

The thalamus is a small section of the midbrain through which most sensory inputs from the body flow. The new findings, which appear in Proceedings of the National Academy of Sciences, indicate that LSD decreases information filtering in the thalamus — allowing more information than normal to flood into the brain.

“LSD and other psychedelics induce unique effects on perception and emotion. These effects could on the one hand be interesting to understand certain symptoms in psychiatric patients (for example schizophrenia), but they could also be clinically beneficial for the treatment of other illnesses (for example depression),” said study author Katrin Preller of the University of Zurich.

“Therefore, understanding how LSD acts in the brain provides information about how our brain works in general and may also have implications for the treatment of psychiatric disorders.”

Based on fMRI data from 25 people, ages 20-34, the researchers found that LSD altered the connectivity between brain regions involved in cortico-striato-thalamo-cortical (CSTC) loop. In particular, there was an increase in connectivity between the thalamus and several regions in the cortex.

“We tested a model that tries to explain how psychedelics work in the brain based on animal studies and that had been around for about 20 years. We showed that this model holds mostly true in humans: The thalamus, which is usually filtering information, sends more information to certain areas in the cortex,” Preller told PsyPost.

“This can explain why psychedelics induce the overwhelming feelings that participants report. It also points to the importance of connections between the thalamus and certain cortical areas in psychiatric symptoms.”

The researchers also found evidence that this was related to serotonergic activity. The serotonin 2A receptor antagonist ketanserin — a drug that blocks serotonin receptors in the brain — inhibited the mind-altering effects of LSD.

But the study — like all research — includes some limitations.

“Currently the method we used only allowed us to test connections between a limited number of brain areas. Testing different brain areas will provide a more complete picture in the future,” Preller said.

The study, “Effective connectivity changes in LSD-induced altered states of consciousness in humans“, was authored by Katrin H. Preller, Adeel Razi, Peter Zeidman, Philipp Stämpfli, Karl J. Friston, and Franz X. Vollenweider.