functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) is an imaging technology used in the book’s account of psychedelic neuroscience to track changes in the living brain while volunteers receive psilocybin or LSD. Its importance is not simply that it renders an altered state visible: paired with volunteers’ reports, it offered a way to relate measurable brain activity to experiences such as Ego dissolution. The resulting picture challenged the expectation that an intense experience must correspond to a more active brain, and focused attention on the Default Mode Network, a system associated with self-reflection, memory, and the familiar boundaries of the self.

A tool for studying altered states

At Imperial College London’s Centre for Psychiatry on the Hammersmith campus, Robin Carhart-Harris and colleagues used fMRI alongside magnetoencephalography (MEG) to investigate the neural correlates of psychedelic experience. Their work began in 2009, after Carhart-Harris had completed a PhD in David Nutt’s lab and obtained approval to study psilocybin’s effects on the brain. Amanda Feilding provided funding. LSD was added to the research program several years later.

The procedure placed volunteers inside a scanner after they had received the drug, allowing the researchers to observe brain changes as the experience unfolded. Carhart-Harris offered to be the first participant, reasoning that he should undergo the procedure himself before asking others to do so. Nutt dissuaded him: Carhart-Harris had described himself as anxious, and Nutt was concerned that taking part could compromise his objectivity. Instead, a colleague became the first volunteer to receive psilocybin and enter the fMRI scanner. The arrangement made the experiment’s human stakes explicit while keeping the researcher in the role of observer.

The unexpected result

Carhart-Harris initially expected brain activity to rise, particularly in areas associated with emotion. That expectation drew partly on earlier findings by Franz Vollenweider, whose data indicated increased activity under psychedelics, especially in the frontal lobes. The first fMRI results pointed in the opposite direction: researchers saw decreases in blood flow, one of the measures used as a proxy for brain activity. A second measure, based on changes in oxygen consumption, corroborated the finding. The decrease was concentrated in the Default Mode Network, a system Carhart-Harris had not yet been studying closely.

The network had been described by Marcus Raichle in 2001, after observations made during the resting-state baseline of fMRI experiments. Volunteers were asked to sit quietly in the scanner before beginning a task. Raichle noticed that several brain areas became more active when participants were doing nothing in particular. These connected regions form a centrally located hub linking parts of the cerebral cortex with deeper structures involved in memory and emotion. In the book’s account, the network is associated with mind-wandering: daydreaming, rumination, mentally revisiting the past or imagining the future, reflecting on oneself, and worrying. The scanner’s resting baseline thus revealed that apparent mental inactivity had its own distinctive pattern of activity.

Connecting scans with experience

The researchers compared the imaging results with volunteers’ descriptions of what they experienced. The steepest reductions in Default Mode Network activity correlated with reports of Ego dissolution: a diminished or lost sense of being a separate self. The greater the fall in blood flow and oxygen consumption in the network, the more likely a volunteer was to report that the ordinary sense of self had weakened. This was a correlation between a measured change and a subjective report, not a direct image of an experience itself; fMRI supplied a physical measure that could be considered alongside what participants said.

The relationship gained another point of comparison when Judson Brewer, studying experienced meditators at Yale, noticed similarities between his fMRI scans and Carhart-Harris’s results. Meditators’ reported transcendence of self, like volunteers’ accounts during psychedelic experiences, was associated with a quieter Default Mode Network. The parallel suggested that different practices or states might share a measurable pattern, without establishing that their experiences were identical. In the book’s interpretation, when activity in this network falls sharply, the usual distinction between self and world—and between subject and object—may temporarily loosen. That possibility offered researchers a way to investigate a feature often associated with mystical experience through both brain measurements and participants’ accounts.

Imaging, prediction, and its limits

The book also connects brain imaging to the broader idea that perception is shaped by prediction. The brain does not simply reproduce the world as a neutral recording; it combines sensory information with expectations drawn from prior experience. A mask experiment described in the book illustrates the effect: under ordinary conditions, a few visual cues can lead the brain to perceive a face as convex even when it is not. That example came from the narrator’s psilocybin experience, not from an fMRI measurement, but it complements the imaging discussion by showing how expectations can organize what is perceived.

These findings make fMRI a means of examining relationships between neural activity and conscious experience, rather than a device that settles what consciousness is. The results connected reduced Default Mode Network activity with self-reported changes and offered a comparison with meditation, while leaving open how those patterns produce the experiences people describe. Its narrative significance lies in that productive gap: a scanner can register shifts in blood flow and oxygen consumption, and volunteers can report a loosening of self, but the relation between those levels remains an object of interpretation. The technology gave psychedelic researchers a new window onto the brain without making the mind transparent.