3 - Precision Grip in Humans: Temporal and Spatial Synergies

Abstract

Publisher Summary Synergy means acting together, without any presupposition as to the source of the coupling. Synergistic processes can either have a common source or drive, or be merely based on spatial or temporal coincidences. This chapter indicates that the control of movement parameters of a clearly specified task does not dictate a unique and deterministic synergistic muscle activation pattern. On the contrary, the central nervous system (CNS) appears to control the task performance and the biomechanical redundancy of the hand by using flexible short-term synergies, predominantly for muscle combinations with task-related, synergic mechanical action. The variable muscle synergies observed do not explain the behavioral consistency and accuracy of grip force production. For grip formation, kinematic invariances have been established for the points of contact between thumb and index finger during dynamic opening and closing of the grip. A basic assumption is that movement specification in systems with redundant degrees of freedom poses a computational problem for the CNS. The chapter also discusses the cooperation of loosely defined descending commands with on-line corrective regulation from peripheral systems.