[Pauses in masseter innervation (silent periods) following stimulation of the median nerve, the cervical plexus and the mental nerve].

In 20 healthy volunteers, a bilateral masseter silent period (Mass SP) was constantly evoked by stimulating the mental nerve (latency: x = 13.95 +/- 4.3 ms) and cervical plexus (latency: x = 20.2 +/- 3.7 ms). This was also the case with median nerve stimulation (latency: x = 54.4 +/- 13.1 ms) in 19 of the 20 subjects. Utilizing magnetic stimulation of the lumbal roots, the Mass SP was elicited in 3 of 10 subjects and showed marked habituation. No Mass SP was observed with stimulation of the long nerves of the lower limbs. The central loop of the reflex represents a stable connection between the spinal cord cervical region and the trigeminal motor nuclei. The Mass SP may be abolished in circumscribed brainstem lesions and thus may serve for localizing lower brainstem involvement.