Effect of spinal cord injury and its lesion level on stretch reflex modulation by cold stimulation in humans

Abstract

Objective To determine how short-latency stretch reflex amplitude in the soleus muscle is modulated by cold stimulation in able-bodied individuals and individuals with complete spinal cord injury. Methods An initial 100-s baseline period was followed by 50-s cold stimulation periods. Stretch reflex of the right soleus muscle was elicited for 10-s intervals, while cold stimulation was applied to the left thigh. Results Peak-to-peak amplitude of the stretch reflex increased significantly during cold stimulation up to 127 ± 21% of the baseline in the able-bodied group ( n = 9, P < 0.01). Similarly, stretch reflex increased up to 125 ± 11% in a group with injury level at or below thoracic 10 ( n = 4), although this increase was not significant. On the other hand, stretch reflex decreased significantly down to 78 ± 20% in a group with injury level at or above thoracic 6 ( n = 8, P < 0.05). Conclusions Effect of afferent inputs induced by cold stimulation on stretch reflex modulation is different depending on the extent of central nervous systems participating in the modulation. Significance Our findings provide a better understanding of some basic changes in afferent–efferent spinal reflex pathways which are probably not monosynaptic in nature.