title: Neural bases of hand synergies.
abstract: The human hand has so many degrees of freedom that it may seem impossible to control. A potential solution to this problem is "synergy control" which combines dimensionality reduction with great flexibility. With applicability to a wide range of tasks, this has become a very popular concept. In this review, we describe the evolution of the modern concept using studies of kinematic and force synergies in human hand control, neurophysiology of cortical and spinal neurons, and electromyographic (EMG) activity of hand muscles. We go beyond the often purely descriptive usage of synergy by reviewing the organization of the underlying neuronal circuitry in order to propose mechanistic explanations for various observed synergy phenomena. Finally, we propose a theoretical framework to reconcile important and still debated concepts such as the definitions of "fixed" vs. "flexible" synergies and mechanisms underlying the combination of synergies for hand control.
authors.affiliation: Neural Control of Movement Laboratory, School of Biological and Health Systems Engineering, Arizona State University Tempe, AZ, USA.
authors.forename: Marco
authors.initials: M
authors.lastname: Santello
authors.forename: Gabriel
authors.initials: G
authors.lastname: Baud-Bovy
authors.forename: Henrik
authors.initials: H
authors.lastname: Jörntell
keywords: degrees of freedom; manipulation; motor cortex; premotor neurons