Brewer

Brewer is a psychiatrist and neuroscientist who studies the brains of meditators. His work gives the book a meeting point between contemplative practice and psychedelic research: he found that experienced meditators and people on Psilocybin show a similar reduction in activity in the default mode network, and he invited the narrator to observe one part of that network in his lab. The resulting experiment did not settle what altered consciousness does, but made the narrator’s remembered psychedelic imagery a possible object of neurological inquiry.

Research on Meditation and the Default Mode Network

Brewer studies the brains of experienced meditators and identified a striking parallel between meditation and Psilocybin: both practices dramatically reduce activity in the default mode network. The comparison places meditation alongside a pharmacological route to altered consciousness without treating the two as identical. It also frames the network as more than an anatomical subject; in the book’s account, its activity is implicated in the mind’s ongoing construction of self.

The focus of Brewer’s lab experiment was the posterior cingulate cortex, a centrally located node within the default mode network. It links the prefrontal cortex, associated with executive function and planning, to the hippocampal centers of memory and emotion. The posterior cingulate cortex is believed to contribute to the experiential or narrative self by generating stories that connect events to a continuing sense of identity.

The Lab Experiment in Worcester

Brewer invited the narrator to the Center for Mindfulness at the University of Massachusetts medical school in Worcester. There, Brewer’s lab used a neural-feedback tool that allowed researchers and volunteers to observe activity in the posterior cingulate cortex in real time. The setup made an abstract theory available as a changing signal: the narrator could see activity in a brain region associated with the stories through which a person relates experience to the self.

During one run, a recollection of a psychedelic experience accompanied a striking drop in the narrator’s measured activity, well below baseline. Brewer asked what the narrator had been thinking and became excited by the possibility that merely recalling a psychedelic experience might reproduce something that happens in the brain during the experience itself. Another possibility was that the particular image—an ego-like structure imagined as detachable—had prompted the change. The experiment offered a question, not a demonstrated explanation.

Self, Craving, and Scientific Uncertainty

Brewer’s account of the posterior cingulate cortex distinguishes having thoughts or feelings from becoming caught up in them. He connected that difference to addiction: experiencing a craving is not the same as being absorbed by it. In this framework, the region’s relevance lies in how a person relates to mental events, and Brewer believes that this operation, when it goes awry, contributes to several forms of suffering, including addiction.

The narrator’s low-activity reading therefore resonated with the book’s earlier account of ego and self-narration, but neither Brewer nor the experiment supplied a final interpretation. Brewer began proposing hypotheses; the narrator recognized that neuroscience at this stage could offer theories and further experiments, not a complete account of consciousness. Brewer’s role in the episode is both practical and intellectual: he provides a tool for looking at brain activity, while the unexpected result sharpens the uncertainty about how meditation, memory, and psychedelic experience intersect.