Skip to content


  • Oral presentation
  • Open Access

Model-based prediction of fusimotor activity during active wrist movements

BMC Neuroscience201314 (Suppl 1) :O16

  • Published:


  • Muscle Spindle
  • Wrist Movement
  • Movement Position
  • Direct Quantification
  • Forward Calculation


Muscle spindles, whose activity is determined by muscle length changes and by fusimotor drive (i.e. γ-drive), provide critical information about movement position and velocity [1]. However, task-dependent fusimotor drive remains largely unknown [2], since no fusimotor neurons have ever been recorded during active, voluntary upper limb movements, whether in animals nor in humans. So far an estimation of γ-drive could only be obtained through an indirect inference of fusimotor activity from observed muscle spindle activity. Our aim was to model the effect of γ-drive on muscle spindles and to simulate voluntary wrist movements for which the spindle responses are empirically known.


Our conceptually simple computational model (an adaptation of [3]) allows for a direct quantification of γ-drive. A forward calculation predicts spindle responses based on time-varying γ-drive and muscle length changes. This computational model thus links a biomechanical (musculo-tendon) wrist model to length- and γ-drive-dependent transfer functions of group Ia and group II muscle spindles. These transfer functions were calibrated (Figure 1A) with extant data from passive movements in the cat [4].
Figure 1
Figure 1

A. Fit between passive [4](dotted lines) and simulated (lines) Ia responses during sinusoidal stretch under constant γ D -drive (125 Hz) and 4 different rates of γ S -drive (top to bottom: 125, 75, 50, 0 Hz). B. Simulated Ia responses (left column) during active muscle contraction for 4 different γS-drives (right column): no, phasic, tonic and phasic-tonic drive. * indicates simulated responses similar to empirically observed Ia responses [5].


Our simulations suggest that (i) empirically observed muscle spindle activity profiles can to a large part be explained by a strongly task-dependent γ-drive (Figure 1B), (ii) observed differences between individual muscle spindle response profiles can be explained by a corresponding variability in the γ-drive (Figure 1B), and (iii) observed phase advance of spindle responses can to a large part be explained by appropriate γ-drive.


Our simulation predicts that γ-drive is strongly modulated and task-dependent and that appropriate γ-drive can explain many empirically observed aspects of group Ia and II muscle spindle responses during active movements.

Authors’ Affiliations

CNRS UMR 8194, Université Paris Descartes, Sorbonne Paris Cité, Paris, F-75006, France
Univ Paris Diderot, Sorbonne Paris Cité, Paris, F-75013, France


  1. Prochazka A: Proprioceptive feedback and movement regulation. Handbook of Physiology Exercise: Regulation and Integration of Multiple Systems. Bethesda, MD, Am Physiol Soc, sect. 12, part I, p. 89-127Google Scholar
  2. Windhorst U: Muscle spindles are multi-functional (Technical comment). Brain Res Bull. 2008, 75: 507-508. 10.1016/j.brainresbull.2007.11.009.View ArticlePubMedGoogle Scholar
  3. Maltenfort MG, Burke RE: Spindle model responsive to mixed fusimotor inputs and testable predictions of beta feedback effects. J Neurophysiol. 2003, 89 (5): 2797-2809. 10.1152/jn.00942.2002.View ArticlePubMedGoogle Scholar
  4. Hulliger M, Matthews PBC, Noth J: Static and dynamic fusimotor action on the response of Ia fibres to low frequency sinusoidal stretching of widely ranging amplitudes. J Physiol (Lond). 1977, 267: 811-836.View ArticleGoogle Scholar
  5. Flament D, Fortier PA, Fetz EE: Response patterns and post-spike effects of peripheral afferents in dorsal root ganglia of behaving monkeys. J Neurophysiol. 1992, 67: 875-889.PubMedGoogle Scholar


© Grandjean and Maier; licensee BioMed Central Ltd. 2013

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.