"If the human brain were so simple that we could understand it, we would be so simple that we couldn't." — Emerson M. Pugh

In a previous piece, I argued that introspection may be our most direct empirical contact with physical reality. Here, we take a deeper dive into how that might be.

Being an interventional psychiatrist—watching people respond rapidly to treatments like transcranial magnetic stimulation, with measurable, specific mechanistic effects that translate directly into subjective experience—has only consolidated this stance. Interventions need to work, and we are best served when we understand exactly how, yet with the best of intentions, we have operated mainly without a coherent theory of how the objective and subjective are related. We are beginning to have the tools to build a better map—and to change the map and therefore change the terrain itself.

What the Brain Does to Know Itself

Start with the body. Before any high-level narrative of selfhood can form, the brain must continuously register what is happening inside the organism—the heartbeat, the gut, the slow thrum of visceral state. This is interoception, mediated primarily through the insula. Neuroanatomist A.D. Craig (2009) proposed a hierarchical model in which the posterior insula maps raw sensations— pain, temperature, organ state—and then, through successive integrations, these become higher-order emotional representations in the anterior insula. What begins as the body's raw telemetry ends as something closer to feeling.

The visceral substrate of selfhood is not an add-on to cognitive self-awareness; in many frameworks, it is its foundation. Neuroimaging shows the anterior insula co-activating with the medial prefrontal cortex during self-reflection: The body and the narrative are not cleanly separable.

At a higher level, the Default Mode Network—medial prefrontal cortex, posterior cingulate, precuneus—continuously updates the autobiographical self (the "wallpaper of the mind"), integrating memory with present state, possibly foundational for core sense of self (Brenner, 2025). Depression shifts these same circuits, the DMN dysregulated as self-referential processing becomes a trap.

Higher up the hierarchy, three more regions complete the picture. The anterior prefrontal cortex supports metacognition—thinking about thinking —and structural differences here predict introspective accuracy with enough precision to........

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