Conduction velocity of the spinothalamic tract in humans as assessed by CO2 laser stimulation of C-fibers

Abstract

We measured the conduction velocity (CV) of C-fibers in the spinothalamic tract (STT) following stimulation with a CO2 laser using a new method. We delivered non-painful laser pulses to tiny areas of the skin overlying the vertebral spinous processes at different levels from the 7th cervical (C7) to the 12th thoracic (T12), and recorded cerebral evoked potentials in 11 healthy men. We used the term ‘ultra-late laser evoked potentials’ (ultra-late LEPs), since the peak latency was much longer than that for conventional LEPs related to Aδ-fibers following painful laser stimulation (late LEPs). The mean CV of C-fibers in the STT was 2.2±0.6 m/s, which was significantly lower than the CV of the Aδ-fibers (10.0±4.5 m/s). This technique is novel and simple, and should be useful as a diagnostic tool for assessing the level of spinal cord lesions.