To evaluate and compare the organization of descending motor pathways to upper extremity muscles among healthy children.
The healthy children were 16 males and 7 females aged 1-19 years (average, 9 years), and eight healthy adults were enrolled as the control group. Transcranial magnetic stimulation was applied to bilateral motor cortices, and motor evoked potentials (MEPs) were recorded using surface electrodes from the first dorsal interossei (FDI), the biceps brachii (BIC), and the deltoid (DEL) muscles. The onset latency, central motor conduction time (CMCT), and amplitude were obtained during a relaxed state.
MEPs of FDI were obtained from subjects aged 13 months. The frequency of obtaining MEPs in proximal and distal muscles increased with age, although there was a less frequent incidence of obtaining MEPs in the proximal BIC and DEL muscles compared with those in the distal FDI muscle. MEP amplitudes increased with age, whereas latencies were relatively constant. CMCTs showed a similar pattern of maturation, and adult values were obtained by 13-years-of-age.
These results suggest that the proximal and distal muscles of the upper extremities show different maturation and organization patterns.
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