Contribution of attentional and cognitive factors to laser evoked brain potentials.

Painful stimuli delivered by infrared laser stimulators elicit laser-evoked potentials (LEP) or magnetic fields in respective electroencephalogram (EEG) and magnetoencephalogram (MEG). Evidence is reviewed that LEP represent a series of event-related potentials (ERP) that depend on vigilance and arousal, selective spatial attention and contextual task variables. Paradigms adopted from other stimulus modalities in the assessment of attention and cognition in ERP and applied to LEP allow the view that middle-latency (N1) and long latency (N2-P2) components of LEP can be overlapped or supplemented by endogenous components such as the processing negativity and distinct members (P3a and P3b) of the "P300" activities, each of which is considered in detail in this review. This composite entity needs to be considered when LEP are experimentally or clinically used in the assessment of sensory and cognitive phenomena and abnormalities of pain sensation.