Complexity in control and planning of human movement
complex behavior, motor learning, movement patterns
Abstract: Several studies have shown evidence of complex behavior in the human nervous
system. Despite the complex and highly variable architecture of the nervous system,
humans present motor behaviors that are consistent across subjects and even across tasks.
This indicates that underlying optimization principles are at work, which are responsible for
dealing with many degrees of freedom and with the intrinsically non stationary nature of
sensory inputs. In this study a control model for upper-limb trajectories is presented, which is
based on the segmentation of complex movements in movement elements that maximize
smoothness and minimize movement duration. It is shown that such a model can account for
the movement patterns of several arm reaching and drawing tasks in healthy subjects, as
well as for the strategies of optimization involved in learning a new motor task. Furthermore,
experimental evidence indicates that the complex properties that characterize the model are
an effect of the motor planning process, as opposed to a trivial consequence of the
biomechanical constraints involved in the movement. The results open new possibilities for
monitoring the evolution of subjects along the rehabilitation and motor learning process.