to that observed in the trigeminal complex. They play an important role not only in pain control but also contribute to the organization of contralateral motor responses to noxious stimuli, including movements of the eyes, ears, and mouth. 10 Moreover, Djupsjo ¨backa et al. 2 demonstrated that stimulation of chemosensitive III and IV muscle receptors evoked alterations in both ipsilateral and contralateral muscle spindle afferents modifying the activity of the ␥-muscle-spindle system.
On the other hand, flumanezil, a drug that failed to modify the ␥ motoneuron firing in animals, reverts the effects of diazepam on R1 and R2 but not R3 responses of the BR in man. 1,8 Our results suggest that the alterations in the sensory inflow produced by capsaicin and Shounousui 6 clearly modify the information traveling in the highthreshold unmyelinated fibers present in the trigeminal nerves of man. Such modifications affect the firing of the ipsi-as well as the contralateral ␥ motoneurons producing the changes observed by us in the R3 responses, and, likewise, reinforce previous suggestions that ␥ motoneurons are actually related to the recording of R3 in the BR of man. 4 The three silent periods detected in the BR of man and the unexpected distant effects produced by botulinum toxin injections in patients with hemifacial spasm 3,5 add strength to these new concepts regarding human reflexobiology involving cranial nerve pathways.