Evidence of different spinal pathways for the warmth evoked potentials

ObjectiveTo investigate the presence of multiple spinothalamic pathways for warmth in the human spinal cord.MethodsLaser 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).ResultsThe 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).ConclusionsOur results suggest that the C-N1 and the C-P2 components are generated by two parallel spinal pathways.SignificanceWarmth sensation is subserved by parallel spinothalamic pathways, one probably reaching the SII area, the other the ACC.

► Conduction velocities of the spinothalamic fibers generating either the C-N1 or the C-P2 LEP components are different.
► Warmth spinal pathways have a parallel organization.
► Warmth has a parallel processing in SII area and cingulate gyrus.