EMG responses in humans during painful heterosegmentary stimulation.

The amplitude-temporal parameters of the nociceptive flexor reflex evoked in the upper and lower extremities by painful heterosegmentary electrical stimulation were studied in healthy volunteers. This reflex was detected bilaterally in the muscles of the upper and lower extremities independently of the site of painful stimulation. The maximum amplitude of the reflex was observed in the case, when the segmentary muscle innervation and the application site of painful stimulation coincided. The least latency of the nociceptive flexor reflex was observed after painful stimulation of the ear lobe. It was concluded the nociceptive flexor reflex is not an elementary polysysnaptic spinal reaction, but involves also some supraspinal centers.