Cortical correlates of neuromotor development in healthy children

Objective: To examine the relationship between acquisition of fine motor skills in childhood and development of the motor cortex. Methods: We measured finger tapping speed and mirror movements in 43 healthy right-handed subjects (6–26 years of age). While recording surface electromyographic activity from right and left first dorsal interosseus, we delivered focal transcranial magnetic stimulation (TMS) over the hand areas of each motor cortex. We measured motor evoked potential (MEP) threshold, and ipsilateral (iSP) and contralateral (CSP) silent periods. Results: As children got older, finger speeds got faster, MEP threshold decreased, iSP duration increased and latency decreased. Finger tapping speed got faster as motor thresholds and iSP latency decreased, but was unrelated to CSP duration. In all subjects right hemisphere MEP thresholds were higher than those on the left and duration of right hemisphere CSP was longer than that on the left. Children under 10 years of age had higher left hand mirror movement scores, and fewer left hemisphere iSPs which were of longer duration. Conclusions: Maturation of finger tapping skills is closely related to developmental changes in the motor threshold and iSP latency. Studies are warranted to explore the relationship between these measures and other neuromotor skills in children with motor disorders. Significance: TMS can provide important insights into certain functional aspects of neurodevelopment in children.