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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 knee torque at the beginning of swing increases with shorter initial toe distance from the barrier. (A) Averaged torque profiles hip, knee, and ankle joints for the first 200 ms of the swing phase for long (solid lines) and short (dashed lines) initial toe-to-barrier positions. Note the knee torque is larger for shorter distances for approximately the first 30 ms of swing (shaded area), whereas the initial torques at the ankle and hip joints are very similar at swing onset for both conditions. Knee flexion torques are negative for the geometry of the leg used in the inverse dynamic analysis, while hip and ankle flexion torques are positive. (B) Scatter plot of data from another animal showing the increase in the knee torque at swing onset with decreasing toe-to-barrier distance.
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Figure 5: The knee torque at the beginning of swing increases with shorter initial toe distance from the barrier. (A) Averaged torque profiles hip, knee, and ankle joints for the first 200 ms of the swing phase for long (solid lines) and short (dashed lines) initial toe-to-barrier positions. Note the knee torque is larger for shorter distances for approximately the first 30 ms of swing (shaded area), whereas the initial torques at the ankle and hip joints are very similar at swing onset for both conditions. Knee flexion torques are negative for the geometry of the leg used in the inverse dynamic analysis, while hip and ankle flexion torques are positive. (B) Scatter plot of data from another animal showing the increase in the knee torque at swing onset with decreasing toe-to-barrier distance.

Mentions: In the three adult cats we examined the relationship between the profiles of joint torques, derived from an inverse dynamic analysis of a leading hind leg stepping over the virtual barrier. The joint torque profiles were similar in all three animals. Figure 5A shows, for one animal, the average torque profiles at the hip, knee, and ankle joints for eight trials when the initial toe-to-barrier distance was greater than 16 cm (solid lines), and five trials when this distance was less than 8 cms (dashed lines). At all three joints there was an initial torque in the flexion direction (this is plotted in the negative direction for the knee because, by convention, torques are measured in the anticlockwise direction so the clockwise flexion torque at the knee in the leg geometry we analyzed (Figure 1) is negative. The most notable feature of the plots shown in Figure 5A is that for the hip and ankle joints the flexion torques at the start of swing are similar for the two starting positions, whereas the flexion torque at swing onset at the knee is larger for the steps starting close to the barrier than for the steps starting a long distance from the barrier. Figure 5B is a scatter plot of data from another animal showing a progressive increase in knee torque as the toe-to-barrier distance decreases. This dependency was found to be significant in all three animals (R2 = 0.290, p < 0.001, n = 39; R2 = 0.208, p < 0.001, n = 55; R2 = 0.121, p = 0.003, n = 72; T-tested using TDIST in Microsoft Excel). By contrast, there was no significant dependence of the initial torques at the hip and ankle joints on the initial distance of the toe from the barrier. R2 values for the hip joint were 0.009 (p = 0.82, n = 39), 0.001(p = 0.49, n = 55), and 0.003 (p = 0.63, n = 72) and for ankle they were 0.042 (p = 0.21, n = 55), 0.043 (p = 0.14, n = 55), and 0.002 (p = 0.71, n = 72). The dependence of knee torque on distance indicates that increases in neural commands to knee flexors is required to fully produce the appropriate amount of knee flexion to avoid the remembered barrier when the initial toe position is close to the barrier. That is, increased motor commands to knee flexor muscles are required to produce the needed increase in the initial slope of the toe trajectory.


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 knee torque at the beginning of swing increases with shorter initial toe distance from the barrier. (A) Averaged torque profiles hip, knee, and ankle joints for the first 200 ms of the swing phase for long (solid lines) and short (dashed lines) initial toe-to-barrier positions. Note the knee torque is larger for shorter distances for approximately the first 30 ms of swing (shaded area), whereas the initial torques at the ankle and hip joints are very similar at swing onset for both conditions. Knee flexion torques are negative for the geometry of the leg used in the inverse dynamic analysis, while hip and ankle flexion torques are positive. (B) Scatter plot of data from another animal showing the increase in the knee torque at swing onset with decreasing toe-to-barrier distance.
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Figure 5: The knee torque at the beginning of swing increases with shorter initial toe distance from the barrier. (A) Averaged torque profiles hip, knee, and ankle joints for the first 200 ms of the swing phase for long (solid lines) and short (dashed lines) initial toe-to-barrier positions. Note the knee torque is larger for shorter distances for approximately the first 30 ms of swing (shaded area), whereas the initial torques at the ankle and hip joints are very similar at swing onset for both conditions. Knee flexion torques are negative for the geometry of the leg used in the inverse dynamic analysis, while hip and ankle flexion torques are positive. (B) Scatter plot of data from another animal showing the increase in the knee torque at swing onset with decreasing toe-to-barrier distance.
Mentions: In the three adult cats we examined the relationship between the profiles of joint torques, derived from an inverse dynamic analysis of a leading hind leg stepping over the virtual barrier. The joint torque profiles were similar in all three animals. Figure 5A shows, for one animal, the average torque profiles at the hip, knee, and ankle joints for eight trials when the initial toe-to-barrier distance was greater than 16 cm (solid lines), and five trials when this distance was less than 8 cms (dashed lines). At all three joints there was an initial torque in the flexion direction (this is plotted in the negative direction for the knee because, by convention, torques are measured in the anticlockwise direction so the clockwise flexion torque at the knee in the leg geometry we analyzed (Figure 1) is negative. The most notable feature of the plots shown in Figure 5A is that for the hip and ankle joints the flexion torques at the start of swing are similar for the two starting positions, whereas the flexion torque at swing onset at the knee is larger for the steps starting close to the barrier than for the steps starting a long distance from the barrier. Figure 5B is a scatter plot of data from another animal showing a progressive increase in knee torque as the toe-to-barrier distance decreases. This dependency was found to be significant in all three animals (R2 = 0.290, p < 0.001, n = 39; R2 = 0.208, p < 0.001, n = 55; R2 = 0.121, p = 0.003, n = 72; T-tested using TDIST in Microsoft Excel). By contrast, there was no significant dependence of the initial torques at the hip and ankle joints on the initial distance of the toe from the barrier. R2 values for the hip joint were 0.009 (p = 0.82, n = 39), 0.001(p = 0.49, n = 55), and 0.003 (p = 0.63, n = 72) and for ankle they were 0.042 (p = 0.21, n = 55), 0.043 (p = 0.14, n = 55), and 0.002 (p = 0.71, n = 72). The dependence of knee torque on distance indicates that increases in neural commands to knee flexors is required to fully produce the appropriate amount of knee flexion to avoid the remembered barrier when the initial toe position is close to the barrier. That is, increased motor commands to knee flexor muscles are required to produce the needed increase in the initial slope of the toe trajectory.

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.