Soleus H and Lower Limb Posterior Root Muscle Reflexes During Stepping After Incomplete SCI

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation Science

Background:

• The soleus H reflex and posterior root muscle (PRM) reflex are crucial for maintaining posture and locomotion.
• Spinal cord injury (SCI) significantly impacts motor control and reflex pathways.
• Understanding reflex modulation during the step cycle is essential for assessing neurological function.

Purpose of the Study:

• To compare step cycle-related modulation of soleus H and PRM reflexes in individuals with and without SCI.
• To investigate the influence of SCI on reflex amplitudes and their modulation during standing and stepping.
• To determine the relationship between reflex modulation and lower extremity motor scores in SCI patients.

Main Methods:

• Recruited 10 neurologically intact subjects and 15 subjects with SCI.
• Utilized a robotic gait orthosis for standing and stepping tasks.
• Measured soleus H reflex and lower limb PRM reflex amplitudes during standing, mid-stance, and mid-swing phases.
• Assessed lower extremity motor scores in the SCI group.

Main Results:

• Both H and PRM reflexes showed step cycle-related modulation in all subjects, but with differing degrees between reflexes.
• The H reflex exhibited greater step cycle-related modulation than the PRM reflex.
• Subjects with SCI displayed higher soleus H and PRM reflex amplitudes and reduced modulation during the step cycle compared to controls.
• Modulation of the soleus H reflex, but not the PRM reflex, correlated with lower extremity motor scores in the SCI group.

Conclusions:

• Impaired step cycle-related reflex modulation in SCI may result from decreased supra-spinal regulation of motoneuron excitability.
• Altered reflex modulation patterns could serve as an indicator of SCI severity and its impact on motor function.
• This study highlights the potential for targeted interventions to improve reflex control and motor recovery in SCI.