Podcast with Hillel Chiel on biomechanics and neural control

Why does understanding the body matter as much as understanding the brain , and how do soft, squishy biomechanics simplify the control problems that nervous systems must solve? Hillel Chiel extracts general principles from tongues, worms, and sea slugs. Subscribe for more from the Convergent Science Network podcast series. Hillel Chiel's research program rests on a foundational claim: evolution selects not for brains or bodies in isolation, but for the coupled dynamical system of brain, body, and environment. This means that understanding neural control without understanding biomechanics is like studying software without knowing the hardware it runs on. His work systematically demonstrates how mechanical properties of soft tissues constrain and simplify the control problems that nervous systems face , often dramatically. The tongue provides a vivid entry point. Modeled as a muscular hydrostat (a "hot dog in a bun" of longitudinal and circumferential muscles), the tongue's geometry creates a massive mechanical advantage for the longitudinal muscle when the tongue is extended. A simple pulse of neural activation produces rapid shortening that the circumferential muscle cannot resist until the tongue is already retracted. The control implication is striking: for a single lapping motion, the nervous system can effectively ignore one of the two muscle groups. This simplification is invisible without biomechanical analysis and would never be predicted from neural recordings alone. Chiel then scales up to peristaltic locomotion, challenging the standard view that it is slow and energetically wasteful. His mathematical analysis of continuous (rather than segmental) peristaltic waves shows that, properly configured, the center of mass can maintain constant velocity without depending on external friction , meaning the energy costs come from internal tissue properties rather than ground contact losses. A one-meter robot built on this principle moves fast enough that you have to walk briskly to keep up. The Aplysia feeding system illustrates the principle that what a muscle does depends on its mechanical context. As the geometry of the feeding apparatus changes during a bite, swallow, or rejection, the same muscle can switch from protraction to retraction. This means that multifunctional behavior arises not from dedicated muscles for each action but from changing coalitions of muscles recruited according to the current biomechanical state. Chiel frames this as a general principle: the nervous system exploits context-dependent mechanics to achieve behavioral flexibility with minimal rewiring, ganging degrees of freedom together for simple movements and fractionating them when precision is needed.