A BIOADAPTIVE APPROACH FOR EXPERIMENTAL PAIN RESEARCH IN HUMANS USINGLASER-EVOKED BRAIN POTENTIALS

In order to find an experimental approach counteracting habituation in experimental pain research using short infrared laser stimulation in humans we developed a bioadaptive method based on subject's report on painfulness of stimulation (pain report; PR). After determination of t he initial relationship between the energy of the laser stimulus and t he corresponding PRs, the approach continuously adjusts the intensity of noxious stimuli so that PR is kept constant across time. Each diffe rence between the PR evoked by the actual laser stimulus and the desir ed PR leads to an increase or decrease of the laser output energy valu e for the next stimulation with the desired PR proportional to the PR difference as well as to the slope of the initial correlation function between laser energy and corresponding PRs. This method has been appl ied in a study with nine volunteers. Results show that the approach le ads to a constant PR by increasing the laser output energy by 0.01 mJ/ s per mm(2) on the average. Furthermore, an analysis of the laser-evok ed brain potentials (LEPs) recorded from Cz was performed for the firs t and second half of stimuli. However, no significant changes in laten cies or amplitudes of the main LEP components recorded at 210 ms (N210 ) and 350 ms (P350) were found. The method seems to be useful for diff erent approaches in experimental and clinical pain research. (C) 1997 Elsevier Science ireland Ltd.