Direct isolation of ultra-late (C-fibre) evoked brain potentials by CO2 laser stimulation of tiny cutaneous surface areas in man.

In this study, it is reported that CO2 laser heat stimulation of tiny skin surface area (0.15 mm2) provides a unique method to directly and selectively activate C-fibre as assessed by the ultra-late brain potentials (peak latencies: N810, P996) evoked consistently across a set of stimulus energy levels. On a larger surface area (15.5 mm2), low energy stimulation also resulted in minute ultra-late potential, while higher intensities induced only late potentials related to A-delta fibre activity (peak latencies: N247, P394). The selective activation of C afferent sensory terminals in the skin by stimulation of tiny surface area is explained by their relative high density and lower activation threshold