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

We measured the conduction velocity (CV) of C-fibers in the spinothalamic t ract (STT) following stimulation with a CO2 laser using a new method. We de livered non-painful laser pulses to tiny areas of the skin overlying the ve rtebral spinous processes at different levels from the 7(th) cervical (C7) to the 12(th) 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 convention al LEPs related to A delta -fibers following painful laser stimulation (lat e 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 Ab-fibers (10.0 +/- 4.5 m/s). This t echnique is novel and simple, and should be useful as a diagnostic tool for assessing the level of spinal cord lesions. (C) 2001 Published by Elsevier Science Ireland Ltd.