New study sheds light on how LSD’s entropic effects on the brain impact language production

Language produced under the influence of the psychedelic drug lysergic acid diethylamide (LSD) displays increased levels of entropy and reduced semantic coherence, according to new research published in the journal Consciousness and Cognition. In other words, people tend to have more disorganized speech while under the effects of LSD and are more likely to jump from one topic to another.

Entropy is a measure of uncertainty and randomness in a system. The concept was originally developed by physicists to measure lost energy in mechanical systems, but more recently it has been used to quantify spontaneous activity in brain networks.

“A few years ago, together with Robin Carhart-Harris and other colleagues, we proposed that the effects of psychedelic drugs are mediated by increased disorganization (or entropy) of brain activity patterns. The increased entropy of brain activity is thus the physical counterpart of the less predictable contents of consciousness that are manifest under the acute effects of psychedelic drugs,” said study author Enzo Tagliazucchi, a professor at the University of Buenos Aires and director of the Consciousness, Culture And Complexity Lab.

“This hypothesis received strong support from neuroimaging experiments in humans, but we speculated that signals of increased brain activity entropy should also be present in behavioral data, in particular, in the flow of natural language production. This is why we decided to investigate whether psychedelics have a disorganizing effect on natural speech,” Tagliazucchi explained.

In the study, 20 healthy participants visited a neuroimaging lab twice, where they either received one dose of LSD or one dose of placebo before undergoing functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) scans. The two experimental sessions occurred at least two weeks apart and the order of the dosing was randomized. After each brain scan, the researchers interviewed the participants regarding their thoughts and feelings during the experience.

Tagliazucchi and his colleagues then used computer algorithms to analyze the participants’ speech patterns. They found that participants under the effects of LSD scored higher on a measure of speech disorganization compared to the placebo condition. LSD also increased the verbosity of speech while reducing its lexicon. In other words, participants tended to use more words after taking LSD, but their vocabulary was relatively smaller.

“Language is a window into our mental processes. If our mental processes become less organized, as a consequence of psychiatric illness or due to the effects of certain drugs, then language should reflect this loss of coherence,” Tagliazucchi told PsyPost.

“We investigated language produced under the acute effects of LSD, a typical psychedelic drug, and found that the drug reduced the semantic coherence of natural language. In simple terms, this means that language produced under the acute effects of LSD is characterized by rapid changes in content, to the point of becoming confusing or hard to follow.”

But the study suffers from a limitation that is common in psychedelic research — participants can easily discern whether they have consumed LSD or an inactive placebo.

“A major limitation of this and other studies of psychedelic drugs is that a control condition is hard to design. Subjects are aware that they received LSD (instead of a placebo) and this changes their attitude towards the experiment immediately. In particular, subjects tend to speak more under LSD compared to the placebo, simply because there are more interesting things to discuss,” Tagliazucchi explained.

“We did not force subjects to produce the same amount of language during the control condition, so there could be a confounding effect related to the length of the verbal reports.”

The study, “The entropic tongue: Disorganization of natural language under LSD“, was authored by Camila Sanz, Carla Pallavicini, Facundo Carrillo, Federico Zamberlan, Mariano Sigman, Natalia Mota, Mauro Copelli, Sidarta Ribeiro, David Nutt, Robin Carhart-Harris, and Enzo Tagliazucchi.