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Spinal mechanisms may provide a combination of intermittent and continuous control of human posture: predictions from a biologically based neuromusculoskeletal model.

Elias LA, Watanabe RN, Kohn AF - PLoS Comput. Biol. (2014)

Bottom Line: Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface.These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control.Another finding was the occurrence of the so-called "paradoxical" behaviour of muscle fibre lengths as a function of postural sway.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Engineering Laboratory, Escola Polit├ęcnica, University of Sao Paulo, Sao Paulo, Brazil.

ABSTRACT
Several models have been employed to study human postural control during upright quiet stance. Most have adopted an inverted pendulum approximation to the standing human and theoretical models to account for the neural feedback necessary to keep balance. The present study adds to the previous efforts in focusing more closely on modelling the physiological mechanisms of important elements associated with the control of human posture. This paper studies neuromuscular mechanisms behind upright stance control by means of a biologically based large-scale neuromusculoskeletal (NMS) model. It encompasses: i) conductance-based spinal neuron models (motor neurons and interneurons); ii) muscle proprioceptor models (spindle and Golgi tendon organ) providing sensory afferent feedback; iii) Hill-type muscle models of the leg plantar and dorsiflexors; and iv) an inverted pendulum model for the body biomechanics during upright stance. The motor neuron pools are driven by stochastic spike trains. Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface. Interesting findings were that: i) an intermittent pattern of muscle activation emerged from this posture control model for two of the leg muscles (Medial and Lateral Gastrocnemius); and ii) the Soleus muscle was mostly activated in a continuous manner. These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control. Another finding was the occurrence of the so-called "paradoxical" behaviour of muscle fibre lengths as a function of postural sway. The simulations confirmed previous conjectures that reciprocal inhibition is possibly contributing to this effect, but on the other hand showed that this effect may arise without any anticipatory neural control mechanism.

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Pooled histogram of centre of mass (COM) displacements from the simulations performed on Model 2.The mean values of COM displacement (mean equilibrium positions of the inverted pendulum) were subtracted from each simulated COM time series so that the data from different simulation runs could be pooled and hence plotted in the same graph. Note that the histogram exhibits a clear bimodal shape (see text for details).
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pcbi-1003944-g003: Pooled histogram of centre of mass (COM) displacements from the simulations performed on Model 2.The mean values of COM displacement (mean equilibrium positions of the inverted pendulum) were subtracted from each simulated COM time series so that the data from different simulation runs could be pooled and hence plotted in the same graph. Note that the histogram exhibits a clear bimodal shape (see text for details).

Mentions: A final quantitative validation was based on the pooled histogram of COM displacements (1-mm bins) as shown in Figure 3 (data are from the simulations of Model 2). The histogram shape was bimodal, with two peaks around the equilibrium position of the inverted pendulum (value 0 in the abscissa). The Jarque-Bera goodness-of-fit test was applied to verify if this histogram could be fitted by a typical Gaussian probability density function [11]. The -hypothesis (the histogram comes from an unimodal Gaussian function) was rejected (). The same result was obtained for Model 1.


Spinal mechanisms may provide a combination of intermittent and continuous control of human posture: predictions from a biologically based neuromusculoskeletal model.

Elias LA, Watanabe RN, Kohn AF - PLoS Comput. Biol. (2014)

Pooled histogram of centre of mass (COM) displacements from the simulations performed on Model 2.The mean values of COM displacement (mean equilibrium positions of the inverted pendulum) were subtracted from each simulated COM time series so that the data from different simulation runs could be pooled and hence plotted in the same graph. Note that the histogram exhibits a clear bimodal shape (see text for details).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230754&req=5

pcbi-1003944-g003: Pooled histogram of centre of mass (COM) displacements from the simulations performed on Model 2.The mean values of COM displacement (mean equilibrium positions of the inverted pendulum) were subtracted from each simulated COM time series so that the data from different simulation runs could be pooled and hence plotted in the same graph. Note that the histogram exhibits a clear bimodal shape (see text for details).
Mentions: A final quantitative validation was based on the pooled histogram of COM displacements (1-mm bins) as shown in Figure 3 (data are from the simulations of Model 2). The histogram shape was bimodal, with two peaks around the equilibrium position of the inverted pendulum (value 0 in the abscissa). The Jarque-Bera goodness-of-fit test was applied to verify if this histogram could be fitted by a typical Gaussian probability density function [11]. The -hypothesis (the histogram comes from an unimodal Gaussian function) was rejected (). The same result was obtained for Model 1.

Bottom Line: Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface.These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control.Another finding was the occurrence of the so-called "paradoxical" behaviour of muscle fibre lengths as a function of postural sway.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Engineering Laboratory, Escola Polit├ęcnica, University of Sao Paulo, Sao Paulo, Brazil.

ABSTRACT
Several models have been employed to study human postural control during upright quiet stance. Most have adopted an inverted pendulum approximation to the standing human and theoretical models to account for the neural feedback necessary to keep balance. The present study adds to the previous efforts in focusing more closely on modelling the physiological mechanisms of important elements associated with the control of human posture. This paper studies neuromuscular mechanisms behind upright stance control by means of a biologically based large-scale neuromusculoskeletal (NMS) model. It encompasses: i) conductance-based spinal neuron models (motor neurons and interneurons); ii) muscle proprioceptor models (spindle and Golgi tendon organ) providing sensory afferent feedback; iii) Hill-type muscle models of the leg plantar and dorsiflexors; and iv) an inverted pendulum model for the body biomechanics during upright stance. The motor neuron pools are driven by stochastic spike trains. Simulation results showed that the neuromechanical outputs generated by the NMS model resemble experimental data from subjects standing on a stable surface. Interesting findings were that: i) an intermittent pattern of muscle activation emerged from this posture control model for two of the leg muscles (Medial and Lateral Gastrocnemius); and ii) the Soleus muscle was mostly activated in a continuous manner. These results suggest that the spinal cord anatomy and neurophysiology (e.g., motor unit types, synaptic connectivities, ordered recruitment), along with the modulation of afferent activity, may account for the mixture of intermittent and continuous control that has been a subject of debate in recent studies on postural control. Another finding was the occurrence of the so-called "paradoxical" behaviour of muscle fibre lengths as a function of postural sway. The simulations confirmed previous conjectures that reciprocal inhibition is possibly contributing to this effect, but on the other hand showed that this effect may arise without any anticipatory neural control mechanism.

Show MeSH
Related in: MedlinePlus