LSD flattens the hierarchy of directed information flow in fast whole-brain dynamics

LSD weakens the brain's directed connectivity hierarchy by increasing the balance between senders and receivers of neural signals. This finding supports the REBUS theory, which proposes that psychedelics flatten the hierarchy of information flow in the brain. Analyzing magnetoencephalography data from 16 healthy participants given 75 micrograms of intravenous LSD, the study found that LSD diminishes the asymmetry of directed connectivity averaged over time. Machine learning classifiers distinguished LSD from placebo more accurately when trained on hierarchy metrics than on traditional functional connectivity measures.

Study at a glance

Abstract

Abstract Psychedelics are serotonergic drugs that profoundly alter consciousness, yet their neural mechanisms are not fully understood. A popular theory, RElaxed Beliefs Under pSychedelics (REBUS), posits that psychedelics flatten the hierarchy of information flow in the brain. Here, we investigate hierarchy based on the imbalance between sending and receiving brain signals, as determined by directed functional connectivity. We measure directed functional hierarchy in a magnetoencephalography (MEG) dataset of 16 healthy human participants who were administered a psychedelic dose (75 micrograms, intravenous) of lysergic acid diethylamide (LSD) under four different conditions. LSD diminishes the asymmetry of directed connectivity when averaged across time. Additionally, we demonstrate that machine learning classifiers distinguish between LSD and placebo more accurately when trained on one of our hierarchy metrics than when trained on traditional measures of functional connectivity. Taken together, these results indicate that LSD weakens the hierarchy of directed connectivity in the brain by increasing the balance between senders and receivers of neural signals.