Postexcitatory Silent Period and Transcallosal Inhibition by the Focal Magnetic Stimulation in Normal Children

J Korean Assoc EMG Electrodiagn Med 2000;2(1):44-48.
Published online May 9, 2000.

Abstract

Objectives : Focal transcranial magnetic stimulation can suppress ongoing voluntary electromyographic activity in contralateral and ipsilateral hand muscles, these inhibitions are known as postexcitatory silent period (PSP) and transcallosal inhibition (TI). The purpose of this study was to determine the pattern of PSP, TI and cortically elicited muscle response in nor- mal children below the age of 10 years (group A : n=5; mean age, 7.8 years) and above the age of 10 years (group B: n=5; mean age, 12.6 years) Methods : We used focal transcranial magnetic stimulation for hand associated motor cortex, under the conditions of standard tonic voluntary contraction of small hand muscle Results : PSP was detected in all subjects, mean duration was 130.3 msec in group A and 182.5 msec in group B. TI was totally absent in group A but detected in 4 subjects of group B and mean duration was 18.3 msec. The motor threshold for cortically elicited muscle response was 82% of maximal stimulus intensity in group A and 61% in guoup B. Onset latency of cortically elicited muscle response was not significantly differnet in two groups. Conclusion : PSP duration was shorter and TI was totally absent in group A while PSP and TI in group B were nealy attained the adult value. We proposed that maturation of some direct corticospinal fiber occurred in early childhood but corticospinal and callosal mediated inhibitory function fully developed in late childhood, around the age of 10 years.

Key Words: Magnetic stimulation, Postexcitatory silent period, Transcallosal inhibition