Figure 1. Experimental arrangement used to impose thumb movements and location of hypertonic saline injection sites.

Pain was initiated at 4 locations (dots in figure): the flexor pollicis longus muscle (FPL), a subcutaneous site over FPL (same spot), flexor carpi radialis muscle (FCR), and a subcutaneous site on the dorso-medial aspect of the thumb proximal phalanx. The forearm and hand were supported on a padded splint, which was tilted upward with the forearm at an angle of ∼20 deg.