- Oral presentation
- Open Access
Model-based prediction of fusimotor activity during active wrist movements
- Bernard Grandjean1 and
- Marc A Maier1, 2Email author
https://doi.org/10.1186/1471-2202-14-S1-O16
© Grandjean and Maier; licensee BioMed Central Ltd. 2013
- Published: 8 July 2013
Keywords
- Muscle Spindle
- Wrist Movement
- Movement Position
- Direct Quantification
- Forward Calculation
Introduction
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.
Methods
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].
Results
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.
Conclusion
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
References
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Copyright
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 (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
