title: Emerging and disappearing synergies in a hierarchically controlled system.
abstract: The purpose of the study was to explore the ability of the central nervous system (CNS) to organize synergies at two levels of a hypothetical control hierarchy involved in two-hand, multi-finger tasks. We investigated indices (DeltaV) of finger force co-variation across trials as reflections of synergies stabilizing the total force (F (TOT)). Subjects produced constant force with one or two finger-pairs (from one hand or two hands). In trials starting with one finger-pair, subjects added another finger-pair without changing F (TOT). In trials starting with two finger-pairs, subjects removed one of the finger-pairs without changing F (TOT). Adding or removing a finger-pair resulted in a transient drop in DeltaV computed for the finger-pair that remained active throughout the trial. This drop in DeltaV was seen simultaneously with force changes. Compared to the original steady-state, addition of a finger-pair led to a significant drop in DeltaV at the newly established steady-state. This drop eliminated negative co-variation among finger forces that had stabilized F (TOT). In contrast, in trials starting with two finger-pairs, no negative co-variation between finger forces within-a-pair was seen. Removing a finger-pair led to the emergence of negative co-variation between finger forces at the new steady-state. The DeltaV index computed across two finger-pairs confirmed the existence of negative force co-variation. The emergence and disappearance of force stabilizing synergies within a finger-pair may signal limitations in the ability of the CNS in forming synergies at two different hierarchical levels.
authors: Department of Kinesiology, The Pennsylvania State University, Rec.Hall-21, University Park, PA 16802, USA. slg220@psu.edu
authors: Stacey L
authors: SL
authors: Gorniak
authors: Vladimir M
authors: VM
authors: Zatsiorsky
authors: Mark L
authors: ML
authors: Latash
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D005260:Female; D005385:Fingers / Q000502:physiology*; D007839:Functional Laterality; D006225:Hand / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D015233:Models, Statistical; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time; D013647:Task Performance and Analysis; D013997:Time Factors
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