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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.


Related in: MedlinePlus

Slope of toe trajectories increase with shorter initial toe distances from the barrier in the behaving animal (dash lines and open squares) and in the forward model (solid line and filled circles) driven by averaged torque profiles calculated for a subset of trials starting with toe-to-barrier distances in the range of 16–25 cms. The initial geometry of the leg in each simulated trial was the same as initial geometry of the leg in the corresponding trial of the behaving animal. Note the divergence of the best best-fitting curves as the initial toe-to-barrier distance decreases due to the lower dependence of the modeled slopes on initial distance from the barrier. The three data sets are from three different animals.
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Figure 3: Slope of toe trajectories increase with shorter initial toe distances from the barrier in the behaving animal (dash lines and open squares) and in the forward model (solid line and filled circles) driven by averaged torque profiles calculated for a subset of trials starting with toe-to-barrier distances in the range of 16–25 cms. The initial geometry of the leg in each simulated trial was the same as initial geometry of the leg in the corresponding trial of the behaving animal. Note the divergence of the best best-fitting curves as the initial toe-to-barrier distance decreases due to the lower dependence of the modeled slopes on initial distance from the barrier. The three data sets are from three different animals.

Mentions: To estimate the contribution of mechanical factors in increasing the slope of the trajectory of the toe when its initial position is close to the remembered barrier, we drove the four-link forward model of the hind leg with the same profile of torques for all initial positions of the hind leg. The torque profiles we chose were the averages of torque profiles for the subset of trials in which the initial toe position was at the longest distance from the barrier. Examples of torque profiles for the hip, knee, and ankle joints are shown in Figure 5A. Assuming that the initial mechanical arrangement of the leg does contribute to increasing the slope of the toe trajectory as the toe distance from the barrier decreases as described previously in behaving animals (Pearson and Gramlich, 2010), the main prediction of our forward modeling analysis was that the slopes of the toe trajectories produced by the simulation should increase as the initial toe distance from the barrier decreases. This prediction was found to be correct for the simulations based on biological data from three animals (Figure 3). Figure 3 shows scatter plots of the toe trajectory slopes vs. initial toe distances observed in the behaving animals (dotted lines, open squares) and produced by the simulation (solid line, filled circles). Both sets of data (biological and simulated) show the slope increasing as the toe-to-barrier distance decreases, but the rate of increase is greater for the behavioral data. The reasonably close correspondence between the observed and simulated slopes at large initial toe-to-barrier distances was expected because the simulation was driven by the average profiles of joint torques and angular velocities calculated for the subset of trials starting at large initial toe-to-barrier distances.


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)

Slope of toe trajectories increase with shorter initial toe distances from the barrier in the behaving animal (dash lines and open squares) and in the forward model (solid line and filled circles) driven by averaged torque profiles calculated for a subset of trials starting with toe-to-barrier distances in the range of 16–25 cms. The initial geometry of the leg in each simulated trial was the same as initial geometry of the leg in the corresponding trial of the behaving animal. Note the divergence of the best best-fitting curves as the initial toe-to-barrier distance decreases due to the lower dependence of the modeled slopes on initial distance from the barrier. The three data sets are from three different animals.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: Slope of toe trajectories increase with shorter initial toe distances from the barrier in the behaving animal (dash lines and open squares) and in the forward model (solid line and filled circles) driven by averaged torque profiles calculated for a subset of trials starting with toe-to-barrier distances in the range of 16–25 cms. The initial geometry of the leg in each simulated trial was the same as initial geometry of the leg in the corresponding trial of the behaving animal. Note the divergence of the best best-fitting curves as the initial toe-to-barrier distance decreases due to the lower dependence of the modeled slopes on initial distance from the barrier. The three data sets are from three different animals.
Mentions: To estimate the contribution of mechanical factors in increasing the slope of the trajectory of the toe when its initial position is close to the remembered barrier, we drove the four-link forward model of the hind leg with the same profile of torques for all initial positions of the hind leg. The torque profiles we chose were the averages of torque profiles for the subset of trials in which the initial toe position was at the longest distance from the barrier. Examples of torque profiles for the hip, knee, and ankle joints are shown in Figure 5A. Assuming that the initial mechanical arrangement of the leg does contribute to increasing the slope of the toe trajectory as the toe distance from the barrier decreases as described previously in behaving animals (Pearson and Gramlich, 2010), the main prediction of our forward modeling analysis was that the slopes of the toe trajectories produced by the simulation should increase as the initial toe distance from the barrier decreases. This prediction was found to be correct for the simulations based on biological data from three animals (Figure 3). Figure 3 shows scatter plots of the toe trajectory slopes vs. initial toe distances observed in the behaving animals (dotted lines, open squares) and produced by the simulation (solid line, filled circles). Both sets of data (biological and simulated) show the slope increasing as the toe-to-barrier distance decreases, but the rate of increase is greater for the behavioral data. The reasonably close correspondence between the observed and simulated slopes at large initial toe-to-barrier distances was expected because the simulation was driven by the average profiles of joint torques and angular velocities calculated for the subset of trials starting at large initial toe-to-barrier distances.

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.


Related in: MedlinePlus