Fig. 1. The methodology used for assessment of lidocaine block duration is illustrated. (A ) Stimulation of the caudal brainstem evoked an antidromic action potential in this masseter muscle afferent fiber. (B ) An electronic Von Frey hair was used to determine the mechanical threshold of the afferent as indicated. (C ) Injection of 1,000 mm glutamate (black triangle) into the afferent fiber mechanoreceptive field substantially decreased the mechanical threshold of this afferent fiber. Injection of 37 mm lidocaine into the afferent fiber mechanoreceptive field 40 min later (white triangle) significantly elevated the mechanical threshold of this afferent fiber (solid black bars) for 3 min. (Inset ) Afferent fiber discharge evoked by injection of glutamate into the masseter muscle. Solid gray line = mean threshold; dotted line =+ 2 SD.