The silent period threshold as a measure of corticospinal inhibition.

Corticomotor threshold is a clinically useful concept for defining motor cortex excitability using transcranial magnetic stimulation. Although the silent period duration can be a quantitative measure of corticospinal inhibitory function, its threshold value has not been formally determined. The authors studied 20 right-handed normal subjects and found that silent period threshold was a reproducible parameter that did not vary with age and sex. Its value was significantly lower with left-sided transcranial magnetic stimulation and right-hand recordings. The silent period threshold may be a novel parameter useful for future studies of cortical inhibitory function.