Crossed spinal soleus muscle communication demonstrated by H-reflex conditioning

Area of Science:

• Neuroscience
• Human Physiology
• Motor Control

Background:

• A conditioning volley to the ipsilateral tibial nerve (iTN) inhibits contralateral soleus (cSOL) electromyographic activity at latencies of 37-41 ms.
• This suggests spinal pathways facilitate communication between muscles in opposing limbs.
• The study aimed to investigate if the cSOL H-reflex is similarly inhibited.

Purpose of the Study:

• To determine if the contralateral soleus (cSOL) H-reflex is inhibited by conditioning volleys to the ipsilateral tibial nerve (iTN).
• To explore interlimb spinal communication pathways.
• To quantify spinal pathway activity using H-reflex conditioning.

Main Methods:

• Thirteen subjects participated in two experiments.
• Stimuli were delivered to the iTN at 85% of maximal M-wave (M-max) with a pre-contracted cSOL.
• Test volleys to the contralateral tibial nerve were delivered at various interstimulus intervals (-6 to 100 ms).

Main Results:

• Significant inhibition of the cSOL H-reflex was observed.
• Inhibition occurred when conditioning stimuli preceded the test H-reflex by 3-33 ms.
• This demonstrates a time-dependent inhibitory effect.

Conclusions:

• The findings confirm spinal muscular communication between opposing limbs.
• H-reflex conditioning provides a quantifiable model for studying this interlimb response.
• This pathway's activity can be measured and further investigated.