Neurophysiological characterization of the anterolateral spinal cord neurons contributing to pain perception in man.

These studies have examined threshold, frequency, and refractory period characteristics of a neural population in the anterolateral quandrant (ALQ) of the spinal cord of man, stimulation of which produces pain. Subjects were 18 conscious humans undergoing percutaneous anterolateral cordotomy for relief of intractable pain. Pain could be produced by ALQ stimulation in all subjects. Pain thresholds ranged from 120 to 1000 muA (at 50 pulses/sec; 0.2 msec pulses), but the majority of thresholds were below 300 muA. A linear relationship was found between stimulation frequency and percentage of subjects reporting pain. This relationship ranged from 5 to 25 pulses/sec with 100% reporting pain at 25/sec and 0% at 5/sec. In 2 of 3 subjects, increases in stimulation frequency up to 500/sec did not produce pain when stimulation intensity was below threshold at 50/sec. The neuronal refractory period for pain in these subjects ranged between 1.0 and 2.0 msec, but the majority of relative refractory periods fell between 1.0 and 1.5 msec. The threshold, frequency, and refractory period data obtained in this study are similar to those found for wide dynamic range cells in the ventral half of the dorsal horn in the monkey and suggest that activation of these cells is a sufficient condition to produce pain in man.