Heteronymous feedback from quadriceps onto soleus in stroke survivors

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation Science

Background:

• Altered heteronymous feedback from quadriceps to soleus may contribute to abnormal coactivation after stroke.
• There is a lack of consensus on whether post-stroke individuals exhibit altered heteronymous reflexes and their underlying mechanisms (increased excitation and/or decreased inhibition).

Purpose of the Study:

• To examine heteronymous excitation and inhibition from quadriceps onto soleus in paretic, nonparetic, and control limbs.
• To determine if increased excitation is due to excitatory or reduced inhibitory reflex circuits.
• To investigate the relationship between heteronymous reflex magnitudes and clinical measures of lower limb recovery and walking ability.

Main Methods:

• Investigated heteronymous excitation and inhibition from quadriceps onto soleus in 14 post-stroke individuals and 14 age-matched controls.
• Elicited heteronymous feedback via femoral nerve and quadriceps muscle stimulation during soleus tonic activation.
• Assessed Fugl-Meyer, 10-m walk test, and Mini-BESTest in stroke survivors.

Main Results:

• No significant differences in heteronymous excitation/inhibition onset, duration, or magnitude were found between paretic, nonparetic, and control limbs.
• Quadriceps stimulation yielded half the excitation magnitude compared to femoral nerve stimulation.
• Femoral nerve-elicited paretic limb excitation showed a positive correlation with walking speed in a subset of participants.

Conclusions:

• Heteronymous feedback from quadriceps to soleus, assessed in a seated posture, appears unimpaired post-stroke.
• Quadriceps stimulation may offer a better estimation of heteronymous inhibition in individuals with exaggerated excitation.
• Paretic limb heteronymous excitation, within the normal range, may positively influence walking speed post-stroke.