Evidence of different spinal pathways for the warmth evoked potentials

Objective: to investigate the presence of multiple spinothalamic pathways for warmth in the human spinal cord. Methods: laser evoked potentials to C-fiber stimulation (C-LEPs) were recorded in 15 healthy subjects after warmth stimulation of the dorsal midline at C5, T2, T6, and T10 vertebral levels. This method allowed us to calculate the spinal conduction velocity (CV) in two different ways: (1) the reciprocal of the slope of the regression line was obtained from the latencies of the different C-LEP components, and (2) the distance between C5 and T10 was divided by the latency difference of the responses at the two sites. In particular, we considered the C-N1 potential, generated in the second somatosensory (SII) area, and the late C-P2 response, generated in the anterior cingulate cortex (ACC). Results: the calculated CV of the spinal fibers generating the C-N1 potential (around 2.5 m/s) was significantly different (p < 0.01) from the one of the pathway producing the P2 response (around 1.4 m/s). Conclusions: our results suggest that the C-N1 and the C-P2 components are generated by two parallel spinal pathways. Significance: warmth sensation is subserved by parallel spinothalamic pathways, one probably reaching the SII area, the other the ACC