Perception isn't just about the external world---it's also about the body. Interoception tracks visceral signals: heart rate, breath, gut sensations, muscle tension, temperature. These signals aren't decorative; they set affective tone and salience, shaping what the brain attends to and which actions it selects. When your body signals "something's off"---a faster heartbeat, a tightness in the chest, a pit in the stomach---that's not separate from cognition. It's the substrate of emotion, and emotion is what tells you whether to act and how.

The predictive processing architecture extends to the body: the brain generates predictions about what your heart rate, breathing, and visceral state should be, and when those predictions fail---when bodily state violates expectations---you feel it as affect. George Mandler called this the interruption theory of emotion: automatic routines run smoothly until something interrupts them, and that interruption is the emotion. The bodily prediction error doesn't just signal "something's wrong"; it colours how you interpret the external world and biases which neural pathways get activated.

There's no action without emotion because there's no reason to do anything unless it has affective significance---unless it feels good, bad, urgent, interesting, safe, threatening. Even "rational" decisions are grounded in bodily evaluations of what matters. The peripheral nervous system constantly informs the central nervous system about the state of the body, and that information is the precursor to every decision you make. If you suspect you're being "too emotional" and decide to do something else, that "something else" is still motivated by a bodily sense that it's better---perhaps referencing an imagined future bodily state that feels more favourable than the present one.

António Damásio gave this a concrete mechanism. When you've encountered a situation before and it produced a strong outcome---good or bad---your body tagged that outcome with a visceral signature: a somatic marker. The next time you face a similar situation, the body replays that signature before you've consciously evaluated the options. Your stomach drops, your chest tightens, your hands get clammy---and these markers bias your decision toward or away from the option, often before you're aware of having made a choice. This isn't a metaphor for intuition; it is intuition, running on the body's hardware. And it doesn't always require the body to actually change. Damásio's "as-if body loop" means the brain can simulate the bodily response internally---imagining a scenario triggers much of the same neural machinery as experiencing it. This is why anticipating a difficult conversation produces real anxiety, and why mental rehearsal actually works: the as-if loop runs the somatic evaluation without waiting for the world to provide the stimulus.

The amygdala's role in this is widely misunderstood. Popular neuroscience calls it the "fear centre," but this is badly wrong. The amygdala responds to emotional intensity and salience, not fear specifically. It fires for unexpected rewards, disgusting images, surprising events, and socially threatening faces---anything the system flags as mattering. It's better understood as an intensity dial: it detects that something is emotionally significant and amplifies the visceral response, ensuring the interoceptive signal gets attention. Fear happens to be emotionally significant, but so are desire, novelty, and social threat. The amygdala doesn't tell you what to feel---it tells you how much.

This architecture also explains why state management matters so much for behaviour change. Bodily arousal tunes the system: high arousal (signalled by neuromodulators like norepinephrine and cortisol) tightens predictions and narrows attention---you fall back on familiar routes. Low arousal broadens the aperture---you're more exploratory, more willing to update. If you want a new behaviour to be available under stress, you have to practise it while stressed, because stress is a bodily context, and retrieval depends on matching encoding context. Regulate the body, and you regulate what the system predicts, attends to, and does.