Association and dissociation between laser-evoked potentials and pain perception.

We investigated the relation between the subjective sensation of pain and two different components of the laser evoked potential, namely the vertex response (N220-P350) and an earlier lateralized response (middle-latency NP160). Brain responses to laser stimuli were obtained in 15 subjects under attentive and distractive conditions. Although stimulus intensity was kept constant, it was perceived as significantly higher when subjects attended the stimulation. There was a positive correlation between subjective intensity perception and the amplitude of the vertex potential, but no correlation existed with the middle-latency component. While laser vertex potentials may reflect attentional/perceptual mechanisms that determine subjective experience, the NP160 behaves as a pre-perceptual sensory response that should be advantageous in the assessment of early cortical pain processing.