The effect of lysergic acid diethylamide (LSD) on whole-brain functional and effective connectivity

Lysergic acid diethylamide (LSD) predominantly strengthens interregional connections and reduces self-inhibition across the brain, except in occipital and subcortical regions where connections weaken and self-inhibition increases. These patterns suggest LSD perturbs the brain's excitation/inhibition balance. Whole-brain effective connectivity, assessed via regression dynamic causal modelling of resting-state fMRI data from 45 participants in two placebo-controlled trials, discriminated LSD from placebo with 91.11% accuracy and correlated with global subjective effects, indicating potential for decoding subjective experiences.

Study at a glance

Abstract

Abstract Psychedelics have emerged as promising candidate treatments for various psychiatric conditions, and given their clinical potential, there is a need to identify biomarkers that underlie their effects. Here, we investigate the neural mechanisms of lysergic acid diethylamide (LSD) using regression dynamic causal modelling (rDCM), a novel technique that assesses whole-brain effective connectivity (EC) during resting-state functional magnetic resonance imaging (fMRI). We modelled data from two randomised, placebo-controlled, double-blind, cross-over trials, in which 45 participants were administered 100 μg LSD and placebo in two resting-state fMRI sessions. We compared EC against whole-brain functional connectivity (FC) using classical statistics and machine learning methods. Multivariate analyses of EC parameters revealed predominantly stronger interregional connectivity and reduced self-inhibition under LSD compared to placebo, with the notable exception of weakened interregional connectivity and increased self-inhibition in occipital brain regions as well as subcortical regions. Together, these findings suggests that LSD perturbs the Excitation/Inhibition balance of the brain. Notably, whole-brain EC did not only provide additional mechanistic insight into the effects of LSD on the Excitation/Inhibition balance of the brain, but EC also correlated with global subjective effects of LSD and discriminated experimental conditions in a machine learning-based analysis with high accuracy (91.11%), highlighting the potential of using whole-brain EC to decode or predict subjective effects of LSD in the future.