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Leg mechanics contribute to establishing swing phase trajectories during memory-guided stepping movements in walking cats: a computational analysis.

Pearson KG, Arbabzada N, Gramlich R, Shinya M - Front Comput Neurosci (2015)

Bottom Line: However, an additional contribution of neuronal motor commands was indicated by the fact that the simulated slopes of paw trajectories were significantly less than the observed slopes.Previous studies have shown that a shift in paw position prior to stepping over a barrier changes the paw trajectory to be appropriate for the new paw position.Our data indicate that both mechanical and neuronal factors contribute to this updating process, and that any shift in leg position during the delay period modifies the working memory of barrier location.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Alberta Edmonton, AB, Canada.

ABSTRACT
When quadrupeds stop walking after stepping over a barrier with their forelegs, the memory of barrier height and location is retained for many minutes. This memory is subsequently used to guide hind leg movements over the barrier when walking is resumed. The upslope of the initial trajectory of hind leg paw movements is strongly dependent on the initial location of the paw relative to the barrier. In this study, we have attempted to determine whether mechanical factors contribute significantly in establishing the slope of the paw trajectories by creating a four-link biomechanical model of a cat hind leg and driving this model with a variety of joint-torque profiles, including average torques for a range of initial paw positions relative to the barrier. Torque profiles for individual steps were determined by an inverse dynamic analysis of leg movements in three normal cats. Our study demonstrates that limb mechanics can contribute to establishing the dependency of trajectory slope on the initial position of the paw relative to the barrier. However, an additional contribution of neuronal motor commands was indicated by the fact that the simulated slopes of paw trajectories were significantly less than the observed slopes. A neuronal contribution to the modification of paw trajectories was also revealed by our observations that both the magnitudes of knee flexor muscle EMG bursts and the initial knee flexion torques depended on initial paw position. Previous studies have shown that a shift in paw position prior to stepping over a barrier changes the paw trajectory to be appropriate for the new paw position. Our data indicate that both mechanical and neuronal factors contribute to this updating process, and that any shift in leg position during the delay period modifies the working memory of barrier location.

No MeSH data available.


Slopes of toe trajectories produced by the simulation are generally lower than the slopes for the observed toe trajectories. Each data point in the scatter plots represents the slope of toe trajectory from the simulation (simulated slope) and the slope observed (observed slope) for a single trail. The three sets of data are from trials in three different animals. Note the divergence from the identity line (dashed) as slope increases. The matching of the data points at the low slopes is because the simulations were driven by average torque profiles of a subset of trials at long toe-to-barrier distances that are associated with low slopes (see Figure 3).
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Figure 4: Slopes of toe trajectories produced by the simulation are generally lower than the slopes for the observed toe trajectories. Each data point in the scatter plots represents the slope of toe trajectory from the simulation (simulated slope) and the slope observed (observed slope) for a single trail. The three sets of data are from trials in three different animals. Note the divergence from the identity line (dashed) as slope increases. The matching of the data points at the low slopes is because the simulations were driven by average torque profiles of a subset of trials at long toe-to-barrier distances that are associated with low slopes (see Figure 3).

Mentions: The divergence of the slopes observed in the simulations and in the behaving animals was clearly revealed in scatter plots of model-slope vs. actual-slope (Figure 4). The data points for all three animals are linearly related with the best fitting lines (solid lines) having slopes of 0.34, 0.20, and 0.41 (the dashed lines in Figure 4 are the identity lines with slopes of 1). This dependency was found to be significant in all three animals (R2 = 0.53, p < 0.001, n = 39; R2 = 0.34, p < 0.001, n = 55; R2 = 0.0.56, p < 0.001, n = 72; T-tested using TDIST in Microsoft Excel). Because larger slopes are associated with trials with short toe-to-barrier distance (Figure 3), the plots in Figure 4 show that the increase in model-slopes with shorter toe-to-barrier distance was less pronounced than the increase in actual-slopes with shorter toe-to-barrier distance. The matching of the model-slopes and actual-slopes at low slope values (close to the intersection of the solid and dashed lines) again reflects the fact that the simulation was driven by torque profiles associated with trials starting with large initial toe-to-barrier distance.


Leg mechanics contribute to establishing swing phase trajectories during memory-guided stepping movements in walking cats: a computational analysis.

Pearson KG, Arbabzada N, Gramlich R, Shinya M - Front Comput Neurosci (2015)

Slopes of toe trajectories produced by the simulation are generally lower than the slopes for the observed toe trajectories. Each data point in the scatter plots represents the slope of toe trajectory from the simulation (simulated slope) and the slope observed (observed slope) for a single trail. The three sets of data are from trials in three different animals. Note the divergence from the identity line (dashed) as slope increases. The matching of the data points at the low slopes is because the simulations were driven by average torque profiles of a subset of trials at long toe-to-barrier distances that are associated with low slopes (see Figure 3).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585078&req=5

Figure 4: Slopes of toe trajectories produced by the simulation are generally lower than the slopes for the observed toe trajectories. Each data point in the scatter plots represents the slope of toe trajectory from the simulation (simulated slope) and the slope observed (observed slope) for a single trail. The three sets of data are from trials in three different animals. Note the divergence from the identity line (dashed) as slope increases. The matching of the data points at the low slopes is because the simulations were driven by average torque profiles of a subset of trials at long toe-to-barrier distances that are associated with low slopes (see Figure 3).
Mentions: The divergence of the slopes observed in the simulations and in the behaving animals was clearly revealed in scatter plots of model-slope vs. actual-slope (Figure 4). The data points for all three animals are linearly related with the best fitting lines (solid lines) having slopes of 0.34, 0.20, and 0.41 (the dashed lines in Figure 4 are the identity lines with slopes of 1). This dependency was found to be significant in all three animals (R2 = 0.53, p < 0.001, n = 39; R2 = 0.34, p < 0.001, n = 55; R2 = 0.0.56, p < 0.001, n = 72; T-tested using TDIST in Microsoft Excel). Because larger slopes are associated with trials with short toe-to-barrier distance (Figure 3), the plots in Figure 4 show that the increase in model-slopes with shorter toe-to-barrier distance was less pronounced than the increase in actual-slopes with shorter toe-to-barrier distance. The matching of the model-slopes and actual-slopes at low slope values (close to the intersection of the solid and dashed lines) again reflects the fact that the simulation was driven by torque profiles associated with trials starting with large initial toe-to-barrier distance.

Bottom Line: However, an additional contribution of neuronal motor commands was indicated by the fact that the simulated slopes of paw trajectories were significantly less than the observed slopes.Previous studies have shown that a shift in paw position prior to stepping over a barrier changes the paw trajectory to be appropriate for the new paw position.Our data indicate that both mechanical and neuronal factors contribute to this updating process, and that any shift in leg position during the delay period modifies the working memory of barrier location.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Alberta Edmonton, AB, Canada.

ABSTRACT
When quadrupeds stop walking after stepping over a barrier with their forelegs, the memory of barrier height and location is retained for many minutes. This memory is subsequently used to guide hind leg movements over the barrier when walking is resumed. The upslope of the initial trajectory of hind leg paw movements is strongly dependent on the initial location of the paw relative to the barrier. In this study, we have attempted to determine whether mechanical factors contribute significantly in establishing the slope of the paw trajectories by creating a four-link biomechanical model of a cat hind leg and driving this model with a variety of joint-torque profiles, including average torques for a range of initial paw positions relative to the barrier. Torque profiles for individual steps were determined by an inverse dynamic analysis of leg movements in three normal cats. Our study demonstrates that limb mechanics can contribute to establishing the dependency of trajectory slope on the initial position of the paw relative to the barrier. However, an additional contribution of neuronal motor commands was indicated by the fact that the simulated slopes of paw trajectories were significantly less than the observed slopes. A neuronal contribution to the modification of paw trajectories was also revealed by our observations that both the magnitudes of knee flexor muscle EMG bursts and the initial knee flexion torques depended on initial paw position. Previous studies have shown that a shift in paw position prior to stepping over a barrier changes the paw trajectory to be appropriate for the new paw position. Our data indicate that both mechanical and neuronal factors contribute to this updating process, and that any shift in leg position during the delay period modifies the working memory of barrier location.

No MeSH data available.