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Assessment of Homonymous Recurrent Inhibition during Voluntary Contraction by Conditioning Nerve Stimulation

View Article: PubMed Central - PubMed

ABSTRACT

In humans, the amount of spinal homonymous recurrent inhibition during voluntary contraction is usually assessed by using a peripheral nerve stimulation paradigm. This method consists of conditioning the maximal M-wave (SM stimulus) with prior reflex stimulation (S1), with 10 ms inter-stimulus interval (ISI). The decrease observed between unconditioned (S1 only) and conditioned (S1+SM) reflex size is then attributed to recurrent inhibition. However, during a voluntary contraction, a superimposed SM stimulation leads to a maximal M-wave followed by a voluntary (V) wave at similar latency than the H-reflex. This wave can therefore interfere with the conditioned H-reflex when two different stimulation intensities are used (S1 and SM), leading to misinterpretation of the data. The aim of the present study was to assess if conditioning V-wave response instead of H-reflex, by applying SM for both stimuli (test and conditioning), can be used as an index of recurrent inhibition. Conditioned and unconditioned responses of soleus and medial gastrocnemius muscles were recorded in twelve subjects at 25% and at 50% of maximal voluntary contraction at the usual ISI of 10 ms and an optimal inter-stimulus of 15 ms determined upon M- and V-wave latencies. Conditioned H-reflex (obtained with S1+SM paradigm) was significantly lower than the unconditioned by ~30% on average, meaning that the amount of inhibition was 70%. This amount of recurrent inhibition was significantly lower at higher force level with both methods. Regardless of the level of force or the conditioning ISI, results obtained with V-wave conditioning (SM+SM) were similar at both force levels, linearly correlated and proportional to those obtained with H conditioning. Then, V-wave conditioning appears to be a reliable index of homonymous recurrent inhibition during voluntary contraction.

No MeSH data available.


Calculation of the theoretical range of ISIs.In the upper panel the parameters of the formula used to determine appropriate theoretical interstimulus intervals (ISI) to record conditioned response are depicted. Maximal M-wave latency (Mlat) and V-wave latency (Vlat) were used to estimate these ranges in both SOL and MG muscles. ISI 1 represents the minimal ISI to record conditioned response, and ISI 2 the maximal one. In lower panels, ranges of theoretical ISIs for soleus muscle (SOL) and medial gastrocnemius (MG) are plotted against subjects’ height, for 25% MVC (left panel) and for 50% MVC (right panel). Vertical dotted lines indicate the common range of theoretical optimal ISIs for all subjects.
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pone.0167062.g003: Calculation of the theoretical range of ISIs.In the upper panel the parameters of the formula used to determine appropriate theoretical interstimulus intervals (ISI) to record conditioned response are depicted. Maximal M-wave latency (Mlat) and V-wave latency (Vlat) were used to estimate these ranges in both SOL and MG muscles. ISI 1 represents the minimal ISI to record conditioned response, and ISI 2 the maximal one. In lower panels, ranges of theoretical ISIs for soleus muscle (SOL) and medial gastrocnemius (MG) are plotted against subjects’ height, for 25% MVC (left panel) and for 50% MVC (right panel). Vertical dotted lines indicate the common range of theoretical optimal ISIs for all subjects.

Mentions: In the present study, the common ISI of 10ms [10] was used to ensure that in our conditions the results obtained with the H-reflex maneuver are in accordance with the literature. However, due to the limitations of using a fixed ISI without considering inter-subjects’ variability, particularly subjects’ height, we proposed a calculation allowing to define the range of ISI that allows the antidromic collision between stimulation to occur between stimulation site and spinal motoneurons (Fig 3). It is then possible to determine a priori a range of optimal ISIs by determining a range of theoretical ISI. Such type of calculation was already performed to assess the site where descending command and antidromic volley from nerve stimulation collide to lead to the recording of V-wave (see [16]).


Assessment of Homonymous Recurrent Inhibition during Voluntary Contraction by Conditioning Nerve Stimulation
Calculation of the theoretical range of ISIs.In the upper panel the parameters of the formula used to determine appropriate theoretical interstimulus intervals (ISI) to record conditioned response are depicted. Maximal M-wave latency (Mlat) and V-wave latency (Vlat) were used to estimate these ranges in both SOL and MG muscles. ISI 1 represents the minimal ISI to record conditioned response, and ISI 2 the maximal one. In lower panels, ranges of theoretical ISIs for soleus muscle (SOL) and medial gastrocnemius (MG) are plotted against subjects’ height, for 25% MVC (left panel) and for 50% MVC (right panel). Vertical dotted lines indicate the common range of theoretical optimal ISIs for all subjects.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120836&req=5

pone.0167062.g003: Calculation of the theoretical range of ISIs.In the upper panel the parameters of the formula used to determine appropriate theoretical interstimulus intervals (ISI) to record conditioned response are depicted. Maximal M-wave latency (Mlat) and V-wave latency (Vlat) were used to estimate these ranges in both SOL and MG muscles. ISI 1 represents the minimal ISI to record conditioned response, and ISI 2 the maximal one. In lower panels, ranges of theoretical ISIs for soleus muscle (SOL) and medial gastrocnemius (MG) are plotted against subjects’ height, for 25% MVC (left panel) and for 50% MVC (right panel). Vertical dotted lines indicate the common range of theoretical optimal ISIs for all subjects.
Mentions: In the present study, the common ISI of 10ms [10] was used to ensure that in our conditions the results obtained with the H-reflex maneuver are in accordance with the literature. However, due to the limitations of using a fixed ISI without considering inter-subjects’ variability, particularly subjects’ height, we proposed a calculation allowing to define the range of ISI that allows the antidromic collision between stimulation to occur between stimulation site and spinal motoneurons (Fig 3). It is then possible to determine a priori a range of optimal ISIs by determining a range of theoretical ISI. Such type of calculation was already performed to assess the site where descending command and antidromic volley from nerve stimulation collide to lead to the recording of V-wave (see [16]).

View Article: PubMed Central - PubMed

ABSTRACT

In humans, the amount of spinal homonymous recurrent inhibition during voluntary contraction is usually assessed by using a peripheral nerve stimulation paradigm. This method consists of conditioning the maximal M-wave (SM stimulus) with prior reflex stimulation (S1), with 10 ms inter-stimulus interval (ISI). The decrease observed between unconditioned (S1 only) and conditioned (S1+SM) reflex size is then attributed to recurrent inhibition. However, during a voluntary contraction, a superimposed SM stimulation leads to a maximal M-wave followed by a voluntary (V) wave at similar latency than the H-reflex. This wave can therefore interfere with the conditioned H-reflex when two different stimulation intensities are used (S1 and SM), leading to misinterpretation of the data. The aim of the present study was to assess if conditioning V-wave response instead of H-reflex, by applying SM for both stimuli (test and conditioning), can be used as an index of recurrent inhibition. Conditioned and unconditioned responses of soleus and medial gastrocnemius muscles were recorded in twelve subjects at 25% and at 50% of maximal voluntary contraction at the usual ISI of 10 ms and an optimal inter-stimulus of 15 ms determined upon M- and V-wave latencies. Conditioned H-reflex (obtained with S1+SM paradigm) was significantly lower than the unconditioned by ~30% on average, meaning that the amount of inhibition was 70%. This amount of recurrent inhibition was significantly lower at higher force level with both methods. Regardless of the level of force or the conditioning ISI, results obtained with V-wave conditioning (SM+SM) were similar at both force levels, linearly correlated and proportional to those obtained with H conditioning. Then, V-wave conditioning appears to be a reliable index of homonymous recurrent inhibition during voluntary contraction.

No MeSH data available.