LATENCY JUMP OF RELAXED VERSUS CONTRACTED MOTOR EVOKED-POTENTIALS AS A MARKER OF CORTICOSPINAL MATURATION

Magnetic brain stimulation was carried out in 17 children, aged from 2 to 12 years, in order to investigate the latency difference between relaxed and contracted motor evoked potentials (MEPs) as a function of age. While the latency of contracted MEPs increased in a linear fashion with age and body size, the relaxed MEP latency had a much slower ''maturation,'' which gained the adult value at about 10-12 years of age in parallel with the acquisition of manual skills. The age-related variation of this ''latency jump'' appears to be a specific indicator of maturative phenomena relating to motor systems.