M. Ishikawa et al., Long latency response of the mentalis muscle following transcranial magnetic stimulation with a circular coil in normal subjects, NEUROL RES, 22(5), 2000, pp. 501-504
Short latency response (SLR), middle latency response and long latency resp
onse (LLR) are elicited in facial muscles by transcranial magnetic stimulat
ion. Although it has been said that the LLRs are elicited by the trigeminal
nerve stimulation, a trigeminofacial reflex is recorded easily in normal s
ubjects by the electrical stimulation in orbicularis oculi muscles as a bli
nd reflex, but a trigeminal-facial reflex recorded in orbicularis oris, nam
ely a snout reflex, is more difficult to record in normal subjects. The aim
of this study is to demonstrate the LLR of lower facial muscles (mentalis
muscle) by the transcranial magnetic stimulation, using a circular coil. Th
e transcranial magnetic stimulations were performed over parieto-occipital
scalp with frequencies of random and 0.3 Hz in I I normal subjects and the
responses in the mentalis muscle were recorded. The LLR of the mentalis mus
cle was recorded in all 11 subjects following SLRs. The latency, duration a
nd LLR/SLR ratio were 37.4 msec, 20.3 msec and 9.1%, respectively. The wave
form of the LLR varied trial to trial showing habituation with a stimulatio
n of 0.3 Hz. At this time the LLR of the masseter muscle was not recorded f
ollowing this transmagnetic stimulation. It was suggested that the LLR of t
he mentalis muscle is recorded by the transcranial magnetic stimulation of
the trigeminal nerve with a circular coil. The ease and reliability of thei
r recording make it possible to apply this LLR clinically as well as a blin
k reflex.