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Cortical output to fast and slow muscles of the ankle in the rhesus macaque.

Hudson HM, Griffin DM, Belhaj-Saïf A, Cheney PD - Front Neural Circuits (2013)

Bottom Line: Although it is generally agreed that cortical stimulation yields short latency facilitation of fast muscles, the effects on the slow muscle, soleus, remain controversial.However, while poststimulus suppression (PStS) was observed in all muscles, it was more common in the slow muscle compared to the fast muscles and was as common as facilitation at low stimulus intensities.Overall, our results demonstrate that cortical facilitation of soleus has an organization that is very similar to that of the fast ankle muscles.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City KS, USA.

ABSTRACT
The cortical control of fast and slow muscles of the ankle has been the subject of numerous reports yielding conflicting results. Although it is generally agreed that cortical stimulation yields short latency facilitation of fast muscles, the effects on the slow muscle, soleus, remain controversial. Some studies have shown predominant facilitation of soleus from the cortex while others have provided evidence of differential control in which soleus is predominantly inhibited from the cortex. The objective of this study was to investigate the cortical control of fast and slow muscles of the ankle using stimulus triggered averaging (StTA) of EMG activity, which is a sensitive method of detecting output effects on muscle activity. This method also has relatively high spatial resolution and can be applied in awake, behaving subjects. Two rhesus macaques were trained to perform a hindlimb push-pull task. Stimulus triggered averages (StTAs) of EMG activity (15, 30, and 60 μA at 15 Hz) were computed for four muscles of the ankle [tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus] as the monkeys performed the task. Poststimulus facilitation (PStF) was observed in both the fast muscles (TA, MG, and LG) as well as the slow muscle (soleus) and was as common and as strong in soleus as in the fast muscles. However, while poststimulus suppression (PStS) was observed in all muscles, it was more common in the slow muscle compared to the fast muscles and was as common as facilitation at low stimulus intensities. Overall, our results demonstrate that cortical facilitation of soleus has an organization that is very similar to that of the fast ankle muscles. However, cortical inhibition is organized differently allowing for more prominent suppression of soleus motoneurons.

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Distribution of PStF onset latencies for ankle muscles at 15, 30, and 60 μA stimuli. The values given in parentheses for each graph represent the mean ± SD of the onset latency of the PStF. Muscle abbreviations are the same as in Figure 1.
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Figure 3: Distribution of PStF onset latencies for ankle muscles at 15, 30, and 60 μA stimuli. The values given in parentheses for each graph represent the mean ± SD of the onset latency of the PStF. Muscle abbreviations are the same as in Figure 1.

Mentions: Figure 3 shows the distribution of PStF onset latencies for the ankle muscles at 15, 30, and 60 μA (all effects included). There was a similar distribution of latencies among all muscles, although TA had a clear suggestion of bimodality that was not present in the distributions for other muscles. The minimum onset latency of PStF decreased by 1.9 ms from 15 to 30 μA and by 0.3 ms from 30 to 60 μA (Table 2A). Regardless of muscle, the minimum latency was approximately 12–13 ms (30 and 60 μA). The only exceptions were two effects in MG at 60 μA that were 8 and 10 ms.


Cortical output to fast and slow muscles of the ankle in the rhesus macaque.

Hudson HM, Griffin DM, Belhaj-Saïf A, Cheney PD - Front Neural Circuits (2013)

Distribution of PStF onset latencies for ankle muscles at 15, 30, and 60 μA stimuli. The values given in parentheses for each graph represent the mean ± SD of the onset latency of the PStF. Muscle abbreviations are the same as in Figure 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585439&req=5

Figure 3: Distribution of PStF onset latencies for ankle muscles at 15, 30, and 60 μA stimuli. The values given in parentheses for each graph represent the mean ± SD of the onset latency of the PStF. Muscle abbreviations are the same as in Figure 1.
Mentions: Figure 3 shows the distribution of PStF onset latencies for the ankle muscles at 15, 30, and 60 μA (all effects included). There was a similar distribution of latencies among all muscles, although TA had a clear suggestion of bimodality that was not present in the distributions for other muscles. The minimum onset latency of PStF decreased by 1.9 ms from 15 to 30 μA and by 0.3 ms from 30 to 60 μA (Table 2A). Regardless of muscle, the minimum latency was approximately 12–13 ms (30 and 60 μA). The only exceptions were two effects in MG at 60 μA that were 8 and 10 ms.

Bottom Line: Although it is generally agreed that cortical stimulation yields short latency facilitation of fast muscles, the effects on the slow muscle, soleus, remain controversial.However, while poststimulus suppression (PStS) was observed in all muscles, it was more common in the slow muscle compared to the fast muscles and was as common as facilitation at low stimulus intensities.Overall, our results demonstrate that cortical facilitation of soleus has an organization that is very similar to that of the fast ankle muscles.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City KS, USA.

ABSTRACT
The cortical control of fast and slow muscles of the ankle has been the subject of numerous reports yielding conflicting results. Although it is generally agreed that cortical stimulation yields short latency facilitation of fast muscles, the effects on the slow muscle, soleus, remain controversial. Some studies have shown predominant facilitation of soleus from the cortex while others have provided evidence of differential control in which soleus is predominantly inhibited from the cortex. The objective of this study was to investigate the cortical control of fast and slow muscles of the ankle using stimulus triggered averaging (StTA) of EMG activity, which is a sensitive method of detecting output effects on muscle activity. This method also has relatively high spatial resolution and can be applied in awake, behaving subjects. Two rhesus macaques were trained to perform a hindlimb push-pull task. Stimulus triggered averages (StTAs) of EMG activity (15, 30, and 60 μA at 15 Hz) were computed for four muscles of the ankle [tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus] as the monkeys performed the task. Poststimulus facilitation (PStF) was observed in both the fast muscles (TA, MG, and LG) as well as the slow muscle (soleus) and was as common and as strong in soleus as in the fast muscles. However, while poststimulus suppression (PStS) was observed in all muscles, it was more common in the slow muscle compared to the fast muscles and was as common as facilitation at low stimulus intensities. Overall, our results demonstrate that cortical facilitation of soleus has an organization that is very similar to that of the fast ankle muscles. However, cortical inhibition is organized differently allowing for more prominent suppression of soleus motoneurons.

Show MeSH
Related in: MedlinePlus