MODULAR ORGANIZATION OF MOTOR BEHAVIOR

The issue of translating the planning of arm movements into muscle for ces is discussed in relation to the recent discovery of structures in the spinal cord. These structures contain circuitry that, when activat ed, produce precisely balanced contractions in groups of muscles. Thes e synergistic contractions generate forces that direct the limb toward an equilibrium point in space. Remarkably, the force outputs, produce d by activating different spinal-cord structures, sum vectorially. Thi s vectorial combination of motor outputs might be a mechanism for prod ucing a vast repertoire of motor behaviors in a simple manner.