Plantar cutaneous input modulates differently spinal reflexes in subjects with intact and injured spinal cord

Spinal Cord, 2007 · DOI: 10.1038/sj.sc.3101917 · Published: January 1, 2007

Spinal Cord Injury Neurology Rehabilitation

Simple Explanation

The study investigates how stimulating the sole of the foot affects reflexes in people with and without spinal cord injuries. In people with spinal cord injuries, stimulating the foot sole increased both flexor and extensor muscle activity. In normal subjects, the soleus H-reflex was depressed while the late flexion reflex was absent. These findings suggest that spinal cord injuries disrupt the normal inhibitory mechanisms that control reflexes, leading to overactivity in both flexor and extensor muscles.

Study Duration

Not specified

Participants

9 spinal-intact and 8 sensory–motor incomplete SCI subjects

Evidence Level

Not specified

Key Findings

1
In SCI subjects, plantar cutaneous afferent stimulation facilitated the soleus H-reflex and late flexion reflex.
2
In normal subjects, plantar cutaneous afferent stimulation depressed the soleus H-reflex, and the late flexion reflex was absent.
3
The early flexion reflex was irregularly observed in SCI patients, while in normal subjects a bimodal reflex modulation pattern was observed.

Research Summary

This study investigates the effects of plantar cutaneous afferent excitation on the soleus H-reflex and flexion reflex in both subject groups while seated. Excitation of plantar cutaneous afferents resulted in facilitation of the soleus H-reflex and late flexion reflex in SCI subjects. In normal subjects, the soleus H-reflex was depressed while the late flexion reflex was absent. The effects of plantar cutaneous afferents change following a lesion to the spinal cord leading to exaggerated activity in both flexors and extensors, suggesting impaired modulation of the spinal inhibitory mechanisms.

Practical Implications

Rehabilitation Strategies

Findings should be considered in programs aimed to restore sensorimotor function and promote recovery in SCI patients.

Understanding Spasms

Cutaneous input in relaxed seated SCI patients might contribute to reflexive enhanced leg muscle activity (or muscle spasms).

Further Research

Further research is needed on the sensorimotor integration and its relative contribution to the final common pathway in human SCI.

Study Limitations

1
The study was conducted with subjects seated, which may not reflect reflex patterns during assisted walking.
2
Differentiation between post- and presynaptic mechanisms cannot be fully ascribed.
3
Reflexes were tested without a maintained weak muscle contraction.

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