Cutaneomuscular reflexes recorded from the lower limb in man during different tasks

Area of Science:

• Neuroscience
• Human Physiology
• Motor Control

Background:

• Cutaneomuscular reflexes are neural responses to cutaneous stimulation.
• These reflexes involve both spinal and supraspinal pathways.
• Understanding reflex modulation during different muscle activation states is crucial for motor control research.

Purpose of the Study:

• To investigate the characteristics of cutaneomuscular reflexes in various lower limb and trunk muscles.
• To compare reflex responses during voluntary muscle contraction versus postural muscle activity.
• To elucidate the role of supraspinal pathways in modulating these reflexes.

Main Methods:

• Electrical stimulation of digital nerves in the second toe.
• Electromyography (EMG) recordings from extensor digitorum brevis (EDB), tibialis anterior (TA), soleus (Sol), quadriceps femoris (Quad), and erector spinae (ES) muscles.
• Recordings were performed during voluntary muscle activation and postural muscle activity.

Main Results:

• Reflex responses comprised three components: E1 (early excitation), I1 (inhibition), and E2 (late excitation).
• E1 and I1 were localized to ankle and foot muscles, while E2 was observed in multiple muscles, notably EDB.
• The E2 component was significantly larger during voluntary contraction compared to postural activity.

Conclusions:

• Spinal pathways mediate E1 and I1 components.
• E2 component relies on supraspinal pathways including the sensorimotor cortex and corticospinal tract.
• Supraspinal pathways are more active during voluntary muscle contraction than during postural activity, modulating cutaneomuscular reflexes.