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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.


The magnitude of EMG activity in knee flexor muscles semitendinosus (ST) and medial sartorius (Sartm) increases with shorter initial toe distance from the barrier. The magnitudes of the EMGs were measured over the first 150 ms of burst onset. Data in (A) and (B) are from two different animals. EMG amplitudes measured in arbitrary units (AU).
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Figure 6: The magnitude of EMG activity in knee flexor muscles semitendinosus (ST) and medial sartorius (Sartm) increases with shorter initial toe distance from the barrier. The magnitudes of the EMGs were measured over the first 150 ms of burst onset. Data in (A) and (B) are from two different animals. EMG amplitudes measured in arbitrary units (AU).

Mentions: The results from both the inverse dynamic analysis and the examination of the properties of the forward model indicated that changes in neuronal commands, in addition to changes in leg geometry, are involved in establishing the inverse relationship between the slope of toe trajectories and the initial toe-to-barrier distance (Figure 3). Thus, we predicted that the magnitude of bursts of activity in one or more leg flexor muscles would depend on the initial toe-to-barrier distance. We focused primarily on the activity in knee flexor muscles (ST and Sartm) because the inverse dynamic analysis showed that the knee flexion torque increased as the toe-to-barrier distance decreased (Figure 5). Consistent with this observation we found that the magnitude of the initial burst activity in both ST in all three animals and Sartm in two animals (recording electrodes in the third malfunctioned) increased the closer the initial toe position was to the barrier (Figure 6). This dependency was found to be significant in all cases (p < 0.001; T-tested using TDIST in Microsoft Excel). EMG recordings from the hip flexor IP muscle in two animals did not reveal any dependence on the initial toe-to-barrier distance (p > 0.1 in both animals), which was consistent with the absence of any dependency of the initial hip torque on distance (see previous section).


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)

The magnitude of EMG activity in knee flexor muscles semitendinosus (ST) and medial sartorius (Sartm) increases with shorter initial toe distance from the barrier. The magnitudes of the EMGs were measured over the first 150 ms of burst onset. Data in (A) and (B) are from two different animals. EMG amplitudes measured in arbitrary units (AU).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: The magnitude of EMG activity in knee flexor muscles semitendinosus (ST) and medial sartorius (Sartm) increases with shorter initial toe distance from the barrier. The magnitudes of the EMGs were measured over the first 150 ms of burst onset. Data in (A) and (B) are from two different animals. EMG amplitudes measured in arbitrary units (AU).
Mentions: The results from both the inverse dynamic analysis and the examination of the properties of the forward model indicated that changes in neuronal commands, in addition to changes in leg geometry, are involved in establishing the inverse relationship between the slope of toe trajectories and the initial toe-to-barrier distance (Figure 3). Thus, we predicted that the magnitude of bursts of activity in one or more leg flexor muscles would depend on the initial toe-to-barrier distance. We focused primarily on the activity in knee flexor muscles (ST and Sartm) because the inverse dynamic analysis showed that the knee flexion torque increased as the toe-to-barrier distance decreased (Figure 5). Consistent with this observation we found that the magnitude of the initial burst activity in both ST in all three animals and Sartm in two animals (recording electrodes in the third malfunctioned) increased the closer the initial toe position was to the barrier (Figure 6). This dependency was found to be significant in all cases (p < 0.001; T-tested using TDIST in Microsoft Excel). EMG recordings from the hip flexor IP muscle in two animals did not reveal any dependence on the initial toe-to-barrier distance (p > 0.1 in both animals), which was consistent with the absence of any dependency of the initial hip torque on distance (see previous section).

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.