LSD flattens the hierarchy of directed information flow in fast whole-brain dynamics
bioRxiv – April 25, 2024
Source: medRxiv/bioRxiv/arXiv
Summary
Psychedelics like LSD may revolutionize our understanding of brain connectivity. Research shows that LSD reduces the imbalance in how information flows between brain regions, leading to a more equal exchange of signals. This shift enhances our ability to distinguish psychedelic effects from placebo, suggesting profound impacts on consciousness.
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.