Influence of a light touch reference on cutaneous reflexes from the hand during standing

Area of Science:

• Neuroscience
• Motor Control
• Somatosensation

Background:

• Light touch of a stable surface aids postural control by reducing body sway.
• Unexpected changes in touch can elicit rapid balance adjustments, initially involving leg muscles and later shifting to arm muscles.

Purpose of the Study:

• To investigate how the excitability of sensorimotor pathways, specifically those originating from finger cutaneous afferents, changes with the reliability of a touch reference.
• To test if interlimb and intralimb cutaneous reflexes are modulated by the stability of a tactile cue during postural tasks.

Main Methods:

• Cutaneous reflexes were evoked using transcutaneous electrical stimulation of the median nerve (MED) and radial nerve (RAD).
• Reflex responses were recorded using electromyography in muscles of the ipsilateral arm (anterior deltoid) and leg (soleus).
• Participants performed standing tasks involving stable touch, unstable touch, or no touch.

Main Results:

• Median nerve (MED) reflexes in the soleus muscle (interlimb) were facilitated with stable touch but reduced with unstable touch.
• Median nerve (MED) reflexes in the anterior deltoid muscle (intralimb) were facilitated when touch was unstable.
• Radial nerve (RAD) reflexes in the soleus muscle were unaffected by touch condition, consistent with its non-involved innervation territory.

Conclusions:

• Cutaneous reflexes originating from the hand are rapidly scaled in response to changes in the reliability of tactile input.
• Spinal sensorimotor pathways demonstrate functional reweighting, adapting reflex activity based on the perceived reliability of tactile afferents.
• These findings highlight the dynamic nature of sensorimotor integration in maintaining balance and adapting motor behavior.