Under the peak effect of LSD, the inhibitory influence from the salience network to the default mode network becomes excitatory, and inhibition from the default mode network to the dorsal attention network weakens. These changes in effective connectivity between resting-state networks may reduce their normal anticorrelation, offering a neural mechanism for ego dissolution—the blurring of the boundary between self and world. The findings suggest that alterations in the sense of self across different conscious states depend on the organized balance of effective connectivity among these networks.
Psilocybin, the active compound in magic mushrooms, alters visual perception by changing how brain regions communicate. Under psilocybin, early visual areas and higher visual-association regions showed increased self-inhibition, reducing sensitivity to incoming neural signals. At the same time, top-down feedback from visual-association areas to earlier visual regions was enhanced. This shift in balance—less bottom-up sensitivity and stronger top-down influence—may explain the vivid eyes-closed imagery characteristic of psychedelic experiences. The findings come from a double-blind, placebo-controlled study of 24 healthy adults using functional MRI and dynamic causal modeling, and they advance understanding of both basic visual perception and potential clinical applications.
Classic psychedelics are thought to reduce the precision of belief updating, allowing access to a wider range of hypotheses for making sense of the world. This process in higher cortices may explain their therapeutic effects on internalizing disorders. The authors argue that reduced precision also underlies changes in consciousness known as ego dissolution, and that alterations in consciousness and attention under psychedelics share a common mechanism of reduced precision in Bayesian belief updating. Evidence linking serotonergic receptors to large-scale connectivity changes in the cortex suggests that the precision of Bayesian belief updating may be a mechanism for modifying and investigating consciousness and attention.