Default mode network deactivation

Default mode network deactivation is the reduction in activity of a brain network associated with inward attention, self-reflection, memory, and emotion. In Robin Carhart-Harris’s first psilocybin brain-imaging experiment, the unexpected reduction—not the increase in activity he had anticipated—was concentrated in this network. The finding gained significance when the sharpest declines corresponded with volunteers’ reports of ego dissolution, and later appeared strikingly similar to the scans of experienced meditators. The book presents the result as a possible neural correlate of temporary selflessness, not as a complete explanation of mystical experience.

Discovery in the Scanner

In 2009, after completing his PhD, Carhart-Harris worked in David Nutt’s lab on a study of psilocybin’s effects on the brain. The research had funding from Amanda Feilding and approval from the National Health Service and the Home Office. Carhart-Harris initially offered to be the first volunteer, reasoning that a researcher administering the drug to other people should experience it himself. He told Nutt that he had an anxious disposition and might not be in the best psychological place; Nutt also worried that taking part could compromise his objectivity. A colleague instead became the first volunteer to receive psilocybin and enter an fMRI scanner.

Carhart-Harris expected to see increased activity, especially in regions associated with emotion. That expectation accorded with findings Franz Vollenweider had published using a different scanning technology, which indicated psychedelic-related increases, particularly in the frontal lobes. The initial fMRI results seemed to point in the opposite direction: blood flow had decreased. A second measure, based on oxygen consumption to identify elevated brain activity, corroborated the first finding. The reduction was concentrated in the default mode network, a system Carhart-Harris initially knew little about.

The network had entered neuroscience through brain-imaging research rather than a deliberate search for a self-related system. In 2001, Marcus Raichle described it in a landmark paper. Researchers had noticed that, during the resting-state baseline of an fMRI experiment, certain brain areas became more active when participants had no assigned mental task. The network was understood as a centrally located hub linking parts of the cerebral cortex with deeper structures involved in memory and emotion. Its activity during rest associated it with daydreaming, rumination, mental time travel, self-reflection, and worry.

Activity, Selfhood, and Meditation

The defining result of Carhart-Harris’s experiment was the relationship between changes in the network and participants’ subjective reports. The steepest reductions in default mode network activity correlated with the strongest reported loss of self. One volunteer described existing only as an idea or concept; another reported no longer knowing where the self ended and the surroundings began. Declines in both blood flow and oxygen consumption tracked the likelihood of this experience. The evidence therefore connected a measurable change in the brain with a reported alteration in the boundaries of identity, without establishing that a scan alone could capture what the experience meant to a participant.

After Carhart-Harris published the results in a 2012 paper, Judson Brewer, who was using fMRI to study experienced meditators, noticed a resemblance between his scans and Carhart-Harris’s. In both cases, reported transcendence of self appeared alongside a quieter default mode network. The comparison suggested that psychedelic experience and meditation, despite being different practices, might converge on a similar pattern of brain activity. The book treats this resemblance as evidence for a possible neural association, not proof that the practices produce identical states or that network deactivation by itself explains them.

The proposed connection matters because a bounded self ordinarily separates subject from object and person from surroundings. When that boundary loosens, experience may take on a sense of nonduality or unity. Carhart-Harris’s account offers a possible explanation for why insights during mystical experiences can feel objectively true: judging a perception as merely subjective may depend on a stable sense of subjectivity, which the experience has temporarily disrupted. This is an interpretation of the reported experience, rather than a conclusion directly measured by fMRI.

Possible Routes to Selflessness

The book proposes that a quieted default mode network could accompany mystical experience through more routes than psychedelic use and meditation. Holotropic breathwork, sensory deprivation, fasting, prayer, overwhelming awe, extreme sports, and near-death experiences are also raised as possibilities. The evidence offered here does not include brain scans from all these circumstances; the suggestion is explicitly speculative. It asks whether these states might share a reduction in network activity, not whether their causes or meanings are interchangeable.

Several possible mechanisms are considered. Deactivation might involve restricting blood flow to the network, stimulating serotonin 2A receptors in the cortex, or disturbing the oscillatory rhythms that ordinarily organize brain activity. The account leaves these as possibilities rather than settled explanations. Its broader claim is correspondingly cautious: taking the network temporarily offline may give access to unusual states, including experiences of oneness or ecstasy, even if a physical account of their conditions does not settle their personal or spiritual significance.

Disinhibition and New Connections

The default mode network is also presented as exerting an inhibitory influence on other areas, including limbic regions involved in emotion and memory. David Nutt compared the network’s role to repression; Carhart-Harris proposed that when its activity falls, other systems are let off the leash. Brain scans showed increased blood flow and oxygen consumption in several regions, including limbic areas, under psychedelics. This disinhibition may help explain why emotions, memories, and sometimes long-buried childhood traumas can surface, and why some researchers and psychotherapists see psychedelics as a means of exploring unconscious material.

A further clue comes from research at Imperial College: when the default mode network disintegrated and the sense of self weakened, overall brain connectivity increased, allowing regions that do not ordinarily communicate to form new connections. The book raises the possibility that these connections could appear in experience as new perspectives or meanings—as the joining of previously distant ideas. It does not claim that this account is established. Instead, it places network deactivation at a meeting point between a measurable change in brain organization and a reported transformation in how the self, memory, emotion, and meaning are experienced.