Cortical silent period in the tongue induced by transcranial magnetic stimulation

Cortical silent period (SP) of the limb muscles is thought to reflect the cortical excitability. However, the lingual SP has not been examined precisely even in normal subjects. We investigated SP in the tongue induced by transcranial magnetic stimulation (TMS) in 18 controls. Surface electrodes were placed on the lingual dorsum using a bipolar technique. A round coil (13.5 cm in outer diameter) connected with Magstim 200 stimulator was placed on the motor cortex of the tongue, and the intensity of the stimulation was increased stepwise to maximum. SP was detected in all subjects especially at the contralateral side to the stimulated side, without contamination of peripheral SP. The duration of SP depended on the stimulus intensity, while the degrees of muscle contraction did not influence SP. SP of the tongue showed similar characteristics to that of limb muscles. This suggests that SP of lingual muscles can be clinically useful for the evaluation of corticobulbar excitability.