This page respects the original work's rights terms and independently introduces its bibliography, abstract, main results, and limitations. It is not a full translation.
About this resource
This page introduces a 2012 study that examined changes in brain activity and blood flow during the acute psilocybin state in 2 functional-MRI experiments involving healthy adults. One used arterial spin labeling and the other BOLD signals, each comparing a sample of approximately 15 people against a placebo condition.
This paper is foundational research showing correlations in brain imaging; it did not test therapeutic effects on depression or other conditions. It used intravenous administration as a research method, which has a different time course from oral psilocybin or whole mushrooms.
Study design
Healthy participants underwent MRI scans in psilocybin and placebo conditions. Arterial spin labeling assessed regional cerebral blood flow, while BOLD assessed signals related to blood oxygenation and connectivity among regions. The strength of subjective effects was also recorded, and relationships with imaging changes were explored.
Because the analyses addressed many brain regions and voxels, multiple comparisons and analytical choices are important. Estimates are more likely to be unstable in small samples and require replication in later research.
Content
At the time, psychedelic states were sometimes pictured intuitively as involving a uniform increase in brain activity. By measuring actual blood flow and BOLD signals, the study suggested that activity and connectivity in particular hub regions or networks might decrease or change.
The default mode network, medial prefrontal cortex, thalamus, and other areas were discussed, but MRI signals do not read neural activity itself directly. They are indirect measures mediated through blood flow, vascular responses, and analytical models.
Results
In the psilocybin condition, decreases in cerebral blood flow or BOLD signals were observed in several hub regions, and changes in connectivity among regions were also shown. Some changes were associated with the strength of subjective effects. The authors discussed the possibility that changes in usual network organization relate to the acute experience.
A result of “decreased activity” does not simply mean brain function was impaired, rested, or healed. It is a relative change dependent on the measurement method and time point, and the content of conscious experience cannot be read from imaging alone.
Limitations
Each experiment involved approximately 15 healthy, selected participants. Intravenous administration, the unusual environment inside an MRI scanner, and brief acute measurements cannot be generalized to ceremonies, natural environments, or therapeutic sessions.
Multiple analyses, vascular effects, head motion, expectations, and unblinding may influence results. A correlation cannot establish one-way causation such as a claim that a particular brain region produces a mystical experience.
The 2 imaging methods complement each other, but they were not one large experiment that replicated identical conditions in the same participants. Agreements and differences between the analyses need to be examined separately.
Safety
The MRI research used rigorous screening and monitoring. Acute anxiety, perceptual changes, and changes in blood pressure and heart rate may occur, and confinement in the scanner may add psychological burden. Small studies in healthy adults do not exclude rare adverse events.
This page does not guide routes of administration or self-experimentation. It is important not to convert brain-imaging changes into proof of treatment, safety, or spiritual truth.
Source and rights
Original source: Carhart-Harris RL, et al. Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. Proceedings of the National Academy of Sciences. 2012;109(6):2138–2143. DOI: 10.1073/pnas.1119598109.
Respecting the original article’s rights conditions, this page is a detailed introduction that independently summarizes public bibliographic information and the article’s principal points. It does not reproduce a full translation, images, figures, or tables. The original source takes precedence for exact imaging thresholds and interpretations.