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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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Related in: MedlinePlus

Distribution of PStF (right) and PStS (left) effects obtained from four ankle muscles of the hindlimb at 15, 30, and 60 μA stimuli. Gray bars: fast muscles. Black bars: slow muscle. Muscle abbreviations are the same as in Figure 1.
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Figure 5: Distribution of PStF (right) and PStS (left) effects obtained from four ankle muscles of the hindlimb at 15, 30, and 60 μA stimuli. Gray bars: fast muscles. Black bars: slow muscle. Muscle abbreviations are the same as in Figure 1.

Mentions: Figure 5 shows the distribution of PStF and PStS effects observed in each of the ankle muscles sampled at 15, 30, and 60 μA. Both PStF and PStS effects were observed in each muscle at each stimulus intensity. Overall, PStF was more common than PStS in all four muscles. PStS was most common in SOL, especially at 15 μA where the incidence of PStS was equal to the incidence of PStF. At higher intensities the incidence of PStF compared to PStS in SOL shifted in favor of PStF. Both monkeys exhibited these trends. However, it should be noted that the increased incidence of facilitation with increasing stimulus intensity is likely to be a consequence of the fact that, for clarity, we based the sign of an effect (facilitation or suppression) on the earliest latency component. Because output zones in cortex are mixed and PStF has a shorter latency than PStS, as stimulus intensity increases, changes in the incidence of facilitation and suppression will be biased toward facilitation. Accordingly, results at the 15 μA intensity are likely to be most meaningful relative to questions about the prevalence of facilitation versus suppression in different muscles.


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 (right) and PStS (left) effects obtained from four ankle muscles of the hindlimb at 15, 30, and 60 μA stimuli. Gray bars: fast muscles. Black bars: slow muscle. 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 5: Distribution of PStF (right) and PStS (left) effects obtained from four ankle muscles of the hindlimb at 15, 30, and 60 μA stimuli. Gray bars: fast muscles. Black bars: slow muscle. Muscle abbreviations are the same as in Figure 1.
Mentions: Figure 5 shows the distribution of PStF and PStS effects observed in each of the ankle muscles sampled at 15, 30, and 60 μA. Both PStF and PStS effects were observed in each muscle at each stimulus intensity. Overall, PStF was more common than PStS in all four muscles. PStS was most common in SOL, especially at 15 μA where the incidence of PStS was equal to the incidence of PStF. At higher intensities the incidence of PStF compared to PStS in SOL shifted in favor of PStF. Both monkeys exhibited these trends. However, it should be noted that the increased incidence of facilitation with increasing stimulus intensity is likely to be a consequence of the fact that, for clarity, we based the sign of an effect (facilitation or suppression) on the earliest latency component. Because output zones in cortex are mixed and PStF has a shorter latency than PStS, as stimulus intensity increases, changes in the incidence of facilitation and suppression will be biased toward facilitation. Accordingly, results at the 15 μA intensity are likely to be most meaningful relative to questions about the prevalence of facilitation versus suppression in different muscles.

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