Psilocybin and the default mode network — what does the research actually show?

The DMN is a set of brain regions (medial prefrontal cortex, posterior cingulate cortex, angular gyrus) that are active during self-referential thought, mind-wandering, and autobiographical memory. It's sometimes called the 'ego network' in pop-science writing. Carhart-Harris et al. (2012, PNAS) showed psilocybin decreases blood flow and BOLD signal in key DMN hubs, with the degree of DMN suppression correlating with subjective ego dissolution. The entropy hypothesis — that psilocybin increases neural entropy (disorder) — came from this group as well.

Important nuance: the DMN suppression finding is real but the 'quieting the ego' framing is an oversimplification. More recent work (Luppi et al., 2021) shows psilocybin doesn't simply suppress the DMN — it disrupts the normal segregation between the DMN and task-positive networks, producing anomalous cross-network connectivity. It's less 'silencing' and more 'dissolving normal boundaries between networks.' The REBUS model (Relaxed Beliefs Under Psychedelics, Carhart-Harris & Friston 2019) is the current best theoretical framework — treats psychedelics as reducing top-down predictive priors, allowing bottom-up sensory signals more weight.

The clinical relevance: the degree of 'mystical experience' or ego dissolution during a psilocybin session correlates with therapeutic outcomes across multiple trials. But this isn't necessarily because DMN suppression is the mechanism of antidepressant effect — it may be that the subjective experience drives psychological change through insight, meaning-making, and emotional processing. The neuroimaging and the psychology are both real; the causal direction is still being worked out.