Background and aims:
Laser-evoked potentials (LEPs) are used for the assesment of human nociceptive fibres (A-delta and C-afferents) and are therefore a useful and well-established method to appraise central pain procession. Repetitively applied painful LEPs lead to habituation, measurable by a decrement of the N2/P2 amplitude in healthy subjects. In contrast, neuropathic pain patients e.g. with painful radiculopathy present reduced or abolished LEP-habituation, which makes the LEP-habituation paradigm an interesting tool to detect central sensitization. Nevertheless, the currently used paradigm lasts too long for a clinical application. The aim of this investigation is to determine whether a shorter interstimulus intervall (ISI) still leads to a significant habituation.

Methods: 
In this study, 21 healthy subjects have been tested by applying 100 painful laser stimuli at the back of the right hand using an ISI of 5-7s in comparison to an ISI of 8-12s in previous studies. Subjects had to rate the perceived laser stimuli on a numerical rating scale (0= no pain, 10= worst pain imaginable) after hearing a ping tone.  

Results: 
The results show significant LEP-habituation during the time-course of repetitively applied laser stimuli. The comparison of the two ISIs (i.e. 8-12s and 5-7s) showed no significant difference regarding the habituation of LEPs and pain, i.e. there was a comparable N2/P2 amplitude and pain rating decrement.

Conclusion: 
These results indicate an equivalence of the shorter ISI, which only lasts 10 minutes (compared to 25), with the previously applied LEP habituation paradigm. Thus, in future studies it might possible to save precious time by resorting to this improved LEP habituation paradigm.

THE IMPROVED LASER-EVOKED POTENTIALS HABITUATION PARADIGM