Inhibitory period and late muscular responses after transcranial magnetic stimulation in healthy children

Transcranial magnetic stimulation (TMS) was investigated in 24 healthy children between the ages of 3 and 14 years in order to study late muscular responses (as they are observed in adults) as a function of age and maturation. Muscular responses were recorded bilaterally from the biceps muscle. An early muscular response and several late phenomena can be elicited in children. (i) An inhibitory period following the primary response could preferentially be recorded contralaterally. (ii) During facilitation, a late response was recorded bilaterally. (iii) Without facilitation (during ‘relaxation’), late responses were recorded bilaterally with a latency of between 50–400 ms. The latency of the latter responses depended on the age of the children, and may therefore be useful in monitoring the maturation of the central motor system in infants. Due to small side-to-side differences, the inhibitory period may be diagnostic value in children for detection of unilateral dysfunction of the central nervous system.