Imperial College London’s First Psilocybin Brain-Imaging Experiment

Imperial College London’s First Psilocybin Brain-Imaging Experiment, approved in 2009, brought psilocybin into the scanner and produced a counterintuitive result: rather than simply intensifying activity in the brain, the drug reduced it, with the largest changes concentrated in the default mode network. The finding gave researchers a way to connect volunteers’ reports of losing their ordinary sense of self with measurable changes in brain activity.

Research Begins

Robin Carhart-Harris had first approached David Nutt in 2005, hoping to study psychedelics and dreaming. Nutt considered the proposal unrealistic for a researcher without neuroscience experience, but offered him a PhD beginning with a more conventional study of MDMA and the serotonin system, with the possibility of turning to psychedelics later. In 2009, after completing his PhD and joining Nutt’s laboratory, Carhart-Harris obtained approval from the National Health Service and the Home Office to study psilocybin’s effects on the brain. The work was funded by Amanda Feilding.

Carhart-Harris initially offered to be the first volunteer. He believed that a researcher asking other people to take a drug inside a scanner should be willing to do so himself. He also recognized that he was anxious and might not be in the best psychological state for the experience; Nutt further worried that his participation could compromise his objectivity. A colleague therefore became the first participant to receive an injection of psilocybin and enter the fMRI scanner.

An Unexpected Brain Scan

Carhart-Harris expected the scans to show increased activity, particularly in areas associated with emotion. He imagined the result might resemble the dreaming brain. That expectation had some scientific context: Franz Vollenweider had published findings, using a different scanning technology, suggesting that psychedelics stimulated brain activity, especially in the frontal lobes, which support executive and other higher cognitive functions.

Instead, the first data showed decreases in blood flow, one of the measures used by fMRI as a proxy for brain activity. The unexpected result led the researchers to question whether something had gone wrong. A second measure, based on changes in oxygen consumption to identify areas of elevated activity, supported the initial finding. The team concluded that psilocybin reduced brain activity, with the decrease especially pronounced in the default mode network, a brain network Carhart-Harris had not previously studied in depth.

The Default Mode Network and the Sense of Self

The default mode network had entered brain science only in 2001, when Marcus Raichle described it in a landmark paper. It links regions of the cerebral cortex with deeper structures involved in memory and emotion. Its activity had been noticed during the quiet resting periods that typically serve as a baseline in fMRI experiments: while volunteers waited without a task, certain areas became active. The network was thus associated with mind-wandering, daydreaming, rumination, reflection on the self, and mental travel through time.

The experiment’s most striking subjective correlate was the relationship between reductions in default mode network activity and ego dissolution. Volunteers who experienced the steepest drops in blood flow and oxygen consumption in the network were more likely to report losing their ordinary sense of self and the boundary between themselves and their surroundings. The study did not establish that the network alone creates the self; it did, however, connect the intensity of reported self-loss with a measurable pattern of reduced activity.

Publication and Wider Significance

Carhart-Harris published the results in 2012 in a paper on the neural correlates of the psychedelic state, using fMRI studies with psilocybin. The findings also prompted a comparison beyond drug research. Judson Brewer, whose fMRI work examined experienced meditators, noticed similarities between their scans and Carhart-Harris’s results: reports of transcending the self in meditation were likewise associated with a quieter default mode network.

That convergence made the experiment significant not simply as a record of what psilocybin does to a brain in a scanner, but as evidence linking distinct routes to altered self-experience with changes in a network associated with self-reflection. The study offered a neural correlate for ego dissolution and suggested that ordinary boundaries between self and world may depend, at least in part, on patterns of brain activity that can temporarily diminish.