WHAT DO SYNERGIES DO AT BERNSTEIN'S LEVEL OF SYNERGIES?

Bernstein emphasized two features of the level of synergies: Reduction of the number of degree-of-freedom (DOFs) and ensuring dynamical stability of movements. This commentary makes a point that uniting elemental performance variables at some level of analysis into groups does not reduce the number of DOFs. The concept of redundancy is inapplicable to biological movement and has to be replaced with the concept of abundance. The apparently extra DOFs form a mechanism of ensuring task-specific stability of salient variables and allowing performance of secondary tasks. Ensuring task-specific dynamical stability of movements remains the only valid function of the level of synergies. This level is also responsible for attenuation of stability in preparation to quick actions. Bernstein’s association of this level with structures within the basal ganglia and thalamus has been supported recently by observations of impaired control of stability in patients with disorders of subcortical structures.