LSD, a potent serotonin-receptor agonist, increases global functional connectivity in the human brain, particularly in high-level association cortices and the thalamus, as shown by fMRI. These effects overlap with serotonin 2A receptor densities and correlate with subjective reports of ego dissolution. The drug also enhances communication between normally distinct brain networks, reducing the brain's modular and rich-club organization. This is the first modern human imaging study of LSD's acute effects on brain connectivity, demonstrating that LSD selectively expands global connectivity and blurs perceptual boundaries between self and environment.
People with first episode psychosis and treatment-resistant schizophrenia show reduced ability to stabilize their decision-making strategies in uncertain environments, resembling effects previously seen with the drug ketamine. In two studies, participants completed a probabilistic reversal learning task. Those with first episode psychosis made more errors and shifted strategies too often after misleading feedback. The treatment-resistant schizophrenia group also shifted strategies more, though their overall accuracy was not significantly reduced. Computational modeling revealed that only the treatment-resistant schizophrenia group showed altered confidence-based modulation of responding, similar to ketamine effects, though these modeling results are considered preliminary due to model limitations.