Ayahuasca, a hallucinogenic brew containing serotonergic agonists and reuptake inhibitors, triggers vivid visual imagery during ceremonies. Using functional magnetic resonance imaging while participants performed a closed-eyes imagery task, the brew produced a robust increase in activation across occipital, temporal, and frontal brain areas. In the primary visual area, activation levels matched those of natural image viewing with eyes open. This effect correlated with individual perceptual changes measured by psychiatric scales. Activity in areas BA30 and BA37, linked to episodic memory and contextual associations, was also potentiated. Modulation of BA10, involved in prospective imagination and working memory, was detected. The findings suggest Ayahuasca seeings arise from an extensive network for vision, memory, and intention, lending a sense of reality to inner experiences.
Updating internal models to predict future events relies on both frontal and parietal brain regions involved in uncertainty-driven updating and a separate network for temporal attention. Using fMRI, this study examined how continuous manipulation of temporal prediction engages these networks. Participants viewed periodic (simple harmonic oscillation) and non-periodic (variable acceleration) motion patterns. Non-periodic motion activated the exogenous temporal orienting network, including ventral premotor and inferior parietal cortices, cerebellum, presupplementary motor area, and motion-sensitive area MT+, with a right-hemisphere bias suggesting explicit timing. Periodic motion activated default-mode network midline areas (left DMPFC, ACC, bilateral PCC/PC), indicating the DMN may process contextually expected information and validate prospective internal models. Findings show continuous temporal prediction engages both temporal expectation representations and task-independent internal model updating.