MODULAR ORGANIZATION OF MOTOR BEHAVIOR IN THE FROGS SPINAL-CORD

The complex issue of translating the planning of arm movements into mu scle forces is discussed in relation to the recent discovery of struct ures in the spinal cord. These structures contain circuitry that, when activated, produce precisely balanced contractions in groups of muscl es. These synergistic contractions generate forces that direct the lim b toward an equilibrium point in space. Remarkably, the forte outputs, produced by activating different spinal-cord structures, sum vectoria lly. This vectorial combination of motor outputs might be a mechanism for producing a vast repertoire of motor behaviors in a simple manner.