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

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.

Immersive exposure to simulated visual hallucinations modulates high-level human cognition

“…Psychedelics are serotoninergic drugs that profoundly alter conscious experience, by disrupting the hierarchical organization of the neural dynamics and increasing neural variability in the human brain [1][2][3][4] . Recently, there has been a renewed interest in the application of psychedelic drugs to investigate its role in the treatment of various psychiatric and neurological conditions [5][6][7][8] and as a methodology to experimentally study the neural mechanisms of altered states of consciousness [9][10][11][12][13] . However, the specific contribution of these pharmacological manipulations to the altered perceptual phenomenology is difficult to estimate given that psychedelics have also secondary effects on the physiology of the human body.…”