LSD flattens the hierarchy of directed information flow in fast whole-brain dynamics
Carhart-Harris, R. L., Deco, G., Kringelbach, M. L., Luppi, A. I., Lynn, C., Muthukumaraswamy, S., Nutt, D. J., Roseman, L., Shinozuka, K., Sicignano, D. J., Tewarie, P. K. B.
This pre-print brain imaging study (n=16, MEG) investigates the neural effects of psychedelics, focusing on hierarchy based on directed functional connectivity (FC). Administering LSD to healthy participants, researchers find LSD diminishes the asymmetry of directed connectivity over time and enhances machine learning classifiers' accuracy in distinguishing LSD from placebo based on hierarchy metrics. These findings suggest LSD weakens the brain's directed connectivity hierarchy by balancing neural signal senders and receivers.
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.