REFERRED pain arising in orofacial pain states is probably due to conv
ergence of different somatosensory input onto the medullary dorsal hor
n (MDH). To examine convergence between nociceptive and nonnociceptive
input onto the MDH, the blink reflex (BR) was applied. R1- and R2-com
ponents can be evoked by innocuous stimuli, but only the R2 is elicite
d by painful heat. The BR was elicited by innocuous electrical stimuli
applied to the supraorbital nerve. A conditioning painful heat pulse
which did not evoke any BR was homotopically applied to the left foreh
ead preceding the electrical stimulus by 75 ms. While R1 remained unch
anged, the R2 was facilitated by about 30%. This study demonstrates a
convergence of low-threshold mechanoreceptive and nociceptive inputs o
nto interneurons of the MDH in man. (C) 1998 Lippincott Williams & Wil
kins.