[Coordination of rhythmic movements: a dynamic approach]

The dynamic theoretic approach regards motor coordination not as a supervised sequential planning but as a spontaneous self-organized process. Owing only to transitory local interactions between sensorimotor areas (without any pre-existing motor program) a coherent collective neural behavior should emerge and underlie voluntary rhythmic synergies (in our example, bimanual on-phase and out-of-phase movements). Therefore this collective behavior should govern and reflect functional constraints slaving independent movement of effectors in a global synergy. In order to understand such a process, it proves necessary to study movement from the effector level to the cerebral level, by experimentally ascertaining: (1) the set of all possible synergies for a given movement, (2) the order parameters and the control parameters, (3) the task-dependent laws for the movement of each effector, and (4) the general and slaving laws responsible for the synergy itself which must be qualitatively similar to those applying to cerebral collective behavior. This paper tries to introduce experimental results for bimanual rhythmic movements as well as the main theoretic tools issued from dynamics of dissipative systems located far from equilibrium (order parameter, multistability, bifurcation, fluctuation...) used to grasp the self-organized nature of motor synergies.