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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

Types of effects observed in stimulus triggered averages of ankle muscle EMG activity. Column on left: magnitude of the primary poststimulus facilitation (PStF) or poststimulus suppression (PStS) measured as peak percent change from baseline EMG value just before the onset of the effect. Stimulation at 60 μA and 15 Hz repetition rate.
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Figure 2: Types of effects observed in stimulus triggered averages of ankle muscle EMG activity. Column on left: magnitude of the primary poststimulus facilitation (PStF) or poststimulus suppression (PStS) measured as peak percent change from baseline EMG value just before the onset of the effect. Stimulation at 60 μA and 15 Hz repetition rate.

Mentions: For this study, we analyzed StTAs from the four ankle muscles at each cortical site. Poststimulus facilitation (PStF) and suppression (PStS) effects were computer measured as described by Mewes and Cheney (1991). Each average consisted of an 80 ms epoch, 20 ms pre-trigger and 60 ms post-trigger. A poststimulus effect (PStE) was defined as a peak or trough of EMG activity that rose or fell from baseline and maintained a level exceeding two standard deviations of baseline for a period equal to or greater than 0.75 ms. Baseline EMG activity was measured as the 12 ms period preceding the onset of the effect initially determined by visual inspection. Baseline statistics were then used to determine the onset of the effect as the point where the envelope of the record exceeded two standard deviations of baseline. The magnitude of PStEs was expressed as the peak percentage increase (+ppi) or peak percentage decrease (−ppi) in EMG activity above (PStF) or below (PStS) baseline. To avoid skewing of the data from very weak effects, only PStF effects with a ppi ≥15 and PStS effects with a ppi ≤−15 were included in the analysis (Figure 2).


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)

Types of effects observed in stimulus triggered averages of ankle muscle EMG activity. Column on left: magnitude of the primary poststimulus facilitation (PStF) or poststimulus suppression (PStS) measured as peak percent change from baseline EMG value just before the onset of the effect. Stimulation at 60 μA and 15 Hz repetition rate.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Types of effects observed in stimulus triggered averages of ankle muscle EMG activity. Column on left: magnitude of the primary poststimulus facilitation (PStF) or poststimulus suppression (PStS) measured as peak percent change from baseline EMG value just before the onset of the effect. Stimulation at 60 μA and 15 Hz repetition rate.
Mentions: For this study, we analyzed StTAs from the four ankle muscles at each cortical site. Poststimulus facilitation (PStF) and suppression (PStS) effects were computer measured as described by Mewes and Cheney (1991). Each average consisted of an 80 ms epoch, 20 ms pre-trigger and 60 ms post-trigger. A poststimulus effect (PStE) was defined as a peak or trough of EMG activity that rose or fell from baseline and maintained a level exceeding two standard deviations of baseline for a period equal to or greater than 0.75 ms. Baseline EMG activity was measured as the 12 ms period preceding the onset of the effect initially determined by visual inspection. Baseline statistics were then used to determine the onset of the effect as the point where the envelope of the record exceeded two standard deviations of baseline. The magnitude of PStEs was expressed as the peak percentage increase (+ppi) or peak percentage decrease (−ppi) in EMG activity above (PStF) or below (PStS) baseline. To avoid skewing of the data from very weak effects, only PStF effects with a ppi ≥15 and PStS effects with a ppi ≤−15 were included in the analysis (Figure 2).

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