Spikes alone do not behavior make: why neuroscience needs biomechanics

Neural circuits do not function in isolation; they interact with the physical world, accepting sensory inputs and producing outputs via muscles. Since both these pathways are constrained by physics, the activity of neural circuits can only be understood by considering biomechanics of muscles, bodies, and the exterior world. We discuss how animal bodies have natural stable motions that require relatively little activation or control from the nervous system. The nervous system can substantially alter these motions, by subtly changing mechanical properties such as body or leg stiffness. Mechanics can also provide robustness to perturbations without sensory reflexes. By considering a complete neuromechanical system, neuroscientists and biomechanicians together can provide a more integrated view of neural circuitry and behavior.

► We review the importance of biomechanics in understanding neural circuits.
► The activity in such circuits can be misinterpreted if biomechanics is neglected.
► Mechanical structures may produce complex motions without complex neural control.
► Subtle neural shifts may change behavior by altering effective mechanical properties.
► Mechanical effects may stabilize fast behaviors without sensory reflexes.