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.

Musical Haptics

“…Analyses of intra-individual consistency and inter-player agreement in the (nonverbal) preference and attribute judgments showed that while violinists generally agreed on what particular attributes they look for in an instrument, the perceptual evaluation of the same attributes varied dramatically across individuals, thus resulting in large interplayer differences in the preference for violins. A third experiment [58] and studies by Fritz et al [26,27] and Wollman et al [66,67] reached similar conclusions.…”

“…The entire sensorimotor system, much of which is dedicated to the hand, is implemented following a hierarchical organisation with nuclei in the dorsal column, the brain stem, the midbrain, the cerebellum and ultimately several cortical regions. The considerable literature on the subject can be approached through recent books and surveys [10,51,67].…”

Neural basis for hand muscle synergies in the primate spinal cord

“…This finding suggests that PreM-INs contribute to the synergistic control of primate hand movements (9,(13)(14)(15), but this question has not been examined directly. We hypothesize that if PreM-INs underlie the generation of muscle synergies, then (i) the distribution of muscle fields will exhibit significant clustering corresponding to extant muscle synergies, rather than being uniform, and (ii) the activities of PreM-INs will be temporally associated with the muscle synergies.…”

Unvealing the Principal Modes of Human Upper Limb Movements through Functional Analysis

“…At the muscle level, different works explored patterns of muscle activity whose timing and/or amplitude modulation enables the generation of different movements, see d ' Avella and Lacquaniti (2013) for a review. Synergies have also been identified and defined as covariation patterns of joint angles, e.g., hand postural synergies (Santello et al, 1998(Santello et al, , 2013Mason et al, 2001), or covariation patterns among digit forces [for a review see Zatsiorsky and Latash (2004)]. However, to correctly understand human manipulation, in addition to hand analysis, the role of whole upper limb movements should be also taken into account.…”