Default mode network

The default mode network is a centrally connected brain system associated with self-reflection, memory, and the construction of personal identity. Its importance in the account lies in a striking contrast: a network linked to the ordinary sense of being a distinct self quiets during psilocybin experiences, and the degree of that quieting correlates with volunteers’ reports of ego dissolution. The finding offers a possible neural connection between brain activity and the mystical experience of losing the boundary between oneself and the world, without establishing that the network alone explains such experiences.

Discovery and Brain-Imaging Research

The network entered brain science through an unexpected observation. In 2001, neurologist Marcus Raichle described it in a landmark paper in the Proceedings of the National Academy of Sciences. Researchers using functional magnetic resonance imaging commonly established a resting-state baseline by having volunteers sit quietly in a scanner before undertaking a task. Raichle noticed that several brain areas became more active not during a specific task, but when subjects were doing nothing in particular. Their activity was a feature of the brain’s default mode, rather than evidence that the brain had become inactive.

Robin Carhart-Harris encountered the network while studying the effects of psilocybin. His initial expectation was that psychedelic activity would increase, especially in areas involved in emotion. Instead, the first measurements showed decreases in blood flow, a proxy for brain activity in functional magnetic resonance imaging. A second measure, based on changes in oxygen consumption, supported the initial finding: psilocybin reduced brain activity, with the decrease concentrated in the default mode network. The unexpected result shifted the question from where the drug might increase activity to what the quieter network normally helps organize.

A Hub for the Resting Mind

The default mode network links parts of the cerebral cortex with deeper, older structures involved in memory and emotion. It has a seesaw-like relationship with attentional networks: when attention is called outward by the environment, the default network tends to quiet; when external demands recede, it becomes more active. The resting state, in this sense, is not mentally empty. The network is engaged as the mind wanders, reflects on itself, revisits the past, imagines the future, and worries.

Its activity is associated with metacognitive processes: self-reflection, mental time travel, moral reasoning, and theory of mind, or imagining the mental states of other people. The account also notes that the network is not operational until relatively late in childhood development and that its activity consumes a disproportionate share of the brain’s energy. It is therefore presented not as a passive background, but as part of the machinery supporting complex, inwardly directed thought.

Carhart-Harris describes the brain as hierarchical: higher-level cortical systems exert an inhibitory influence on older systems associated with emotion and memory. In this arrangement, the default mode network functions as a central organizer, coordinating the activity of specialized systems and keeping competing signals from disrupting one another. Its role is compared to that of a conductor or executive: a hub that helps hold the larger system together and restrain its less orderly tendencies. These metaphors emphasize the network’s coordinating function, rather than suggesting that it is a single command center acting alone.

The Network and the Sense of Self

The network’s organizing role extends to mental constructs, above all the self, or ego. Some neuroscientists therefore call it the me network. It becomes active when a person considers whether a list of adjectives applies to them, and it is associated with autobiographical memory: the material through which past experience is connected to present events and future aims to form a story of who one is.

That story supports a distinct identity and a sense of continuity, but the account also describes a cost. A sharply bounded self can bring a sense of separation from other people and from nature. Self-reflection may contribute to intellectual and artistic achievement, while also enabling destructive self-regard and unhappiness. A cited psychological study found a strong correlation between unhappiness and time spent mind-wandering, one of the default network’s principal activities. The argument is not that selfhood is simply harmful, but that a capacity central to human identity can also become a source of distress.

Psilocybin, Ego Dissolution, and Mystical Experience

The most striking result in Carhart-Harris’s first experiment was a correlation between the steepest declines in default mode network activity and volunteers’ subjective reports of ego dissolution. As blood flow and oxygen consumption in the network fell more sharply, volunteers were more likely to describe losing their ordinary sense of self. Their accounts included feeling that they existed only as an idea, or no longer knowing where they ended and their surroundings began. The imaging result thus connected a measurable change in a brain network with a reported change in the experience of self, while remaining a correlation rather than proof of a complete mechanism.

A comparison with meditation offered a further point of reference. After Carhart-Harris published the findings in a 2012 paper in the Proceedings of the National Academy of Sciences, Judson Brewer, who was using functional magnetic resonance imaging to study experienced meditators, noticed similarities between those scans and Carhart-Harris’s results. The transcendence of self reported by expert meditators also appeared alongside a quieter default mode network. The comparison suggests that markedly reduced network activity can accompany more than one route to diminished self-boundaries; it does not make the two states identical.

The proposed connection matters because the loss of individuality and separation is a hallmark of mystical experience. If the sense of self depends in part on a mental construction supported by the default mode network, its temporary quieting may help explain why subject and object can seem to merge. The account extends that possibility to the feeling of certainty that can accompany mystical insight: when a person’s ordinary sense of subjectivity fades, an insight may feel less like one individual’s interpretation and more like a truth revealed. This remains an explanatory proposal, but it gives the network a central place in the book’s attempt to relate neural activity, the experience of self, and the felt authority of mystical understanding.