The default mode network is the seat of the rigid self

Neuroimaging research that Pollan surveys, much of it from Imperial College London's Robin Carhart-Harris, identifies a brain network called the default mode network (DMN) — active during self-referential thought, mind-wandering, and rumination, and closely associated with the sense of having a stable, continuous "self."

The striking finding is that psychedelics like psilocybin and LSD sharply reduce activity and connectivity within the DMN, and depression, addiction, and obsessive rumination are all associated with an overactive, rigidly looping DMN — the same self-critical thoughts cycling on repeat.

This gives psychedelic therapy a specific mechanism, not just a vague "expanded consciousness" story: by quieting the network that enforces habitual, self-referential thought patterns, psychedelics create a temporary window in which entrenched mental grooves — depressive thought loops, addictive cravings, fear of death — can be interrupted and, ideally, not simply resumed afterward.

Takeaway: what psychedelics may treat isn't a chemical deficiency but an overly rigid, habit-locked mode of self-focused thinking.