Offset analgesia and onset hyperalgesia with different stimulus ranges
ABSTRACTOffset analgesia (OA), a large reduction in pain following a brief increase in intensity of an otherwise stable painful stimulus, has been established by a large body of research. But the opposite effect, onset hyperalgesia (OH), a disproportional hyperalgesic response following a briefly decreased intensity of a painful stimulus, has only been investigated in one previous study. The aim of this study was to induce OA and OH in healthy participants and explore the effects of different stimulus ranges on OA and OH. A total of 62 participants were tested in two identical experiments. OA and OH conditions included two different temperature deviations (±1°C/±2°C) from baseline and were compared to a constant temperature (control). OA was successfully elicited in three out of four conditions. A dose-response relationship was demonstrated between the increase of temperature and the resulting hypoalgesic response. OH was only elicited in one out of four conditions (OH2°C in experiment 1). Exploratory analysis showed that OA and OH responses were only weakly correlated. The asymmetry between pain responses following a brief temperature increase and decrease could be seen as evidence for different mechanisms involved in the pain responses to increasing and decreasing temperature. This asymmetry may also be explained by high temperatures in OA condition (+1°C/+2°C above baseline) that could be seen as salient “learning signals”, which augment the response to following changes in temperature.