The role of plant properties in the control of point-to-point arm movements

The hand, in directed point to point arm movements in absence of obstacles, tends to follow smooth, straight paths with bell-shaped velocity profiles. To what extent these features must be programmed by the central nervous system in its time-varying neural signals to the muscles, and to what extent they are, instead, an emergent property of the arm plant, is a controversial matter. We describe here a modeling study that suggests that smoothness of the hand paths and bell-shapedness of the velocity profiles can be accounted for at the level of the plant. Our results suggest that the task of an eventual controller for the arm could simply be that of selecting appropriate amplitudes and durations for the neural inputs without considering additional motor details.