Soleus H-reflex excitability during standing with stable and unstable light touch

Area of Science:

• Neuroscience
• Biomechanics
• Human sensorimotor control

Background:

• Light touch can stabilize posture, especially with eyes closed.
• The sensorimotor system rapidly adapts to unexpected changes in sensory input during postural tasks.

Purpose of the Study:

• To investigate the neurophysiological changes in soleus H-reflex excitability during adaptation to repeated unexpected touch displacements.
• To understand how sensorimotor adaptation to light touch affects postural sway.

Main Methods:

• Measured soleus H-reflex and M-wave excitability, and background muscle activity in ten healthy participants.
• Recorded postural sway using a force plate across five standing conditions (eyes open, eyes open with touch, eyes closed, eyes closed with touch, eyes closed with repeated touch displacement).

Main Results:

• H-reflexes were suppressed and sway increased in eyes closed conditions compared to eyes open.
• In the repeated touch displacement condition, H-reflexes were suppressed similarly to eyes closed, but sway did not increase.
• This suggests a shift in sensorimotor processing from using touch as a spatial reference to a target to be maintained.

Conclusions:

• The sensorimotor system rapidly adapts to changes in light touch during postural control within a single trial.
• Adaptation involves a modulation of spinal reflex excitability, indicated by H-reflex suppression.
• This neurophysiological change reflects a strategic shift in how the brain utilizes sensory information for maintaining balance.