Operculoinsular cortex encodes pain intensity at the earliest stages of cortical processing as indicated by amplitude of laser-evoked potentials in humans

Currently, early and late LEP components are considered to be differentially sensitive to the subjective variability of pain perception: the late N2-P2 complex strongly correlates with perceived pain, whereas the early N1 component is thought to be a pre-perceptual sensory response. To obtain physiological information on the roles of the pain-related brain areas in healthy humans, we examined the relationship between perceived pain intensity and latency and amplitude of the early (N1) and late (N2, P2) LEP components. We found that the amplitude of the N1 component correlated significantly with the subjective pain ratings, both within and between subjects. Furthermore, we showed that the N2 and P2 late LEP components are differentially sensitive to the perceived sensation, and demonstrated that the N2 component mainly explains the previously described correlation between perceived pain and the amplitude of the N2-P2 vertex complex of LEPs. Our findings confirm the notion that pain intensity processing is distributed over several brain areas, and suggest that the intensity coding of a noxious stimulus occurs already at the earliest stage of perception processing, in the operculoinsular region and, possibly, the primary somatosensory area.