Laser evoked brain potentials in response to painful trigeminal nerve activation.

Long latency brain potentials were evoked by infrared laser stimuli (LEPs) applied to the right forehead in order to activate the thinnest cutaneous A-delta afferents of the upper branch of the trigeminal nerve thus inducing a painful sensation. Ten healthy male subjects participated in 4 identical subsequent sessions, one week apart, receiving 4 blocks of 40 stimuli each. This way the individual trigeminal LEPs, as well as their inter- and intraindividual reliability were determined. Five major components could be identified, denoted by polarity and peak latencies: N150, P230, N300, P360, N480. The LEP waveforms were found to be highly stable within subjects, peak latencies varied by less than 5%. Great variation in waveform appeared amongst subjects, peak latencies varied by more than 15%. The last two components exhibited the largest variability and were not identified in all subjects.