Trance, an absorptive state with narrowed external awareness used by shamans for insight, was studied with fMRI in 15 experienced shamanic practitioners listening to rhythmic drumming. During trance, three brain regions—posterior cingulate cortex, dorsal anterior cingulate cortex, and left insula/operculum—showed stronger hubs (higher eigenvector centrality). The posterior cingulate cortex, a default network hub for internal thought, coactivated with control-network regions, suggesting amplified internal neural streams. Auditory pathway seeds were less connected, indicating perceptual decoupling from repetitive drumming. This network reconfiguration may support extended internal thought and insight.
Rhythmic flicker light stimulation at 10 Hz reliably induces transient visual hallucinations in healthy people, while arrhythmic flicker does so less. Using fMRI, rhythmic flicker produced stronger activation in higher order visual cortices and selectively increased connectivity between ventroanterior thalamic nuclei and those cortices, compared to arrhythmic control. The strength of this connectivity correlated positively with the subjective intensity of hallucinations. Because the ventroanterior thalamus and higher order visual areas do not receive primary visual inputs, the findings suggest the thalamus coordinates cortical activity to generate hallucinatory experiences, offering insight into pathological hallucinations.