A hierarchical model of synergistic motor control

Experimental studies of motor control in humans and other animals suggest that complex movements are constructed from a relatively small set of motor primitives representing preferential coordinated activation patterns in groups of muscles. These have been termed synergies. We have previously presented a neurodynamical model of how motor primitives with the observed characteristics of synergies might be encoded in cortico-spinal and spinal neural networks. The model showed that a small basis set of synergies could be used to combinatorially generate linear trajectories in all directions from all points within the posture space of a two-joint, two degree-of-freedom arm. We now present an extension of that model, where useful combinations of these low-level synergies are encoded into higher-level primitives termed hypersynergies, such that the activation of a single hypersynergy with appropriate control parameters allows the generation of an extensive repertoire of movements over large parts of posture space. This repertoire is “exploited” by a cortical motor control system implemented through interacting neural maps. We argue that this system can generate complex movements with relatively simple neural control mechanisms.