Attention-related modifications of ultra-late CO2 laser evoked potentials to human trigeminal nerve stimulation

Our study aimed at investigating the scalp topography of ultra-late CO₂ laser evoked potentials (LEPs), which are related to C fiber activation, and at exploring the effect of attention deviation on ultra-late LEPs. Brain responses to non-painful CO₂ laser stimuli were recorded in ten healthy subjects in three different conditions: (i) neutral condition in which subjects did not have any task; (ii) distraction condition in which subjects were asked to perform a mathematical task; and (iii) attention condition in which subjects had to count the number of stimuli. In all subjects, also Ao fiber-related late LEPs were recorded after painful CO₂ laser stimulation. The ultra-late LEPs in attention condition included an earlier negative potential (ultra-late N1) in the contralateral temporal region and a simultaneous frontal positive response (ultra-late P1). Later, a vertex biphasic component (ultra-late N2a and ultra-late P2) was identifiable. The vertex ultra-late LEP amplitude was significantly decreased in both neutral and distraction condition. Ultra-late LEPs showed a longer latency than late LEPs, but the scalp distributions of both ultra-late and late LEPs were very similar, thus suggesting that the same cerebral areas may be involved in their generation. Since attention deviations have a strong effect on ultra-late LEP amplitude, the subject's attention should be addressed to CO₂ laser stimuli when ultra-late LEPs are used for clinical purposes.