Enhanced short-term sensitization of facial compared to limb heat pain

Habituation and sensitization are important features of the individual sensitivity to repetitive noxious stimulation and have been investigated in numerous studies. It is, however, unclear whether these phenomena vary depending on the site of stimulation. Here we compared short-term and long-term effects of painful heat stimulation on the forehead and limb using an established longitudinal heat pain paradigm performed over eight consecutive days in 36 healthy volunteers. Participants were randomized into two groups that received repetitive heat pain stimulation either on the left volar forearm or on the left side of the forehead, respectively. Our data show a comparable degree of habituation over the course of eight days in both groups. However, participants in the trigeminal stimulation group exhibited stronger within-session sensitization (indexed by a higher within-session increase in pain intensity ratings) than those who received the forearm stimulation. Further, we found a correlation between habituation and anxiety showing less habituation over the course of the experiment in subjects with higher trait anxiety scores. Our findings are in line with somatotopic differences in response to painful stimulation and a higher proneness of trigeminal pain to sensitization processes, which might be explained by the biological relevance of the head and facial area for vital functions. The contribution of this sensitivity to the development and maintenance of clinical facial pain and headache disorders warrants further investigation.

PERSPECTIVE: This study uses psychophysical methods to evaluate the differences in long-term habituation and short-term sensitization to heat pain between the trigeminal and spinal system. We found stronger sensitization for trigeminal compared to nociceptive stimuli on the forearm. The contribution of this sensitivity to clinical pain states warrants further investigation.