Peripheral sensitization reduces laser-evoked potential habituation

Summary Objective Laser-evoked potential (LEP) habituation was investigated under the influence of capsaicin-induced peripheral and central sensitization. Material and methods Fifteen subjects received 100 repetitive painful laser stimuli at the right hand dorsum at primary (application area; condition I) and secondary areas (beyond application area; condition II) in two different sessions after applying capsaicin topically. Conditions I and II were compared to a control condition without capsaicin application. N1, N2, and P2 latencies and N1 and N2/P2 amplitudes were recorded by EEG. Quantitative sensory testing (QST) and the Liewald Diary reaction time experiment were used as control tests. Results QST documented heat hyperalgesia as a sign of peripheral sensitization in the primary area and pinprick hyperalgesia in the primary and secondary area as a sign of central sensitization, after applying capsaicin. The N2/P2 amplitude habituation was significantly reduced in the primary area compared to controls (the primary area represents peripheral sensitization). The LEPs of the secondary area (the secondary area represents central sensitization) showed no significant N2/P2 amplitude habituation compared to controls. The comparison between conditions I vs. II showed no significant difference regarding N2/P2 amplitude and laser pain rating. Conclusion Capsaicin-induced central sensitization does not alter LEP habituation. The physiological habituation of LEP amplitudes is reduced due to peripheral mechanisms after applying capsaicin topically. These findings form a basis for future studies, which use the habituation paradigm to investigate pain conditions promoted by sensitization phenomena.