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Static and dynamic changes in body orientation modulate spinal reflex excitability in humans
Maria Knikou1, William Zev Rymer
1Feinberg School of Medicine, Northwestern University, 345 East Superior, Chicago, IL 60611, USA. m-knikou@northwestern.edu
Experimental Brain Research
|August 9, 2003
Summary
Body angle changes significantly modulate the soleus H reflex. Upright positions depress the reflex, while supine positions facilitate it, demonstrating vestibular system
Area of Science:
- Neuroscience
- Human Physiology
- Motor Control
Background:
- The soleus H reflex is a valuable tool for assessing spinal cord excitability.
- Understanding reflex modulation is crucial for comprehending posture and balance control.
Purpose of the Study:
- To investigate how static and dynamic changes in body angle affect the soleus H reflex in healthy individuals.
- To explore the influence of body orientation and movement on reflex modulation.
Main Methods:
- Soleus H reflexes were recorded in subjects in supine and erect positions.
- Body angle was manipulated using a motorized tilt table from horizontal to beyond upright.
- Subjects were secured with elastic bands to maintain position during tilt.
Main Results:
- The soleus H reflex was significantly depressed (40% of control) in the vertical position.
- Significant reflex facilitation (140-180% of control) was observed at various supine angles.
- Dynamic tilting induced substantial reflex facilitation (up to 300% of control).
Conclusions:
- Body orientation changes profoundly modulate soleus motoneurone excitability.
- Vestibular system stimulation significantly impacts reflex activity, independent of specific angle or movement direction.
- Findings offer insights into the neural mechanisms underlying posture maintenance.