Anisotropy of callosal motor fibers in combination with transcranial magnetic stimulation in the course of motor development.

OBJECTIVES: The corpus callosum (CC) represents a key structure for hand motor development and is accessible to investigation by diffusion tensor magnetic resonance imaging (DTI) and transcranial magnetic stimulation (TMS). To identify quantifiable markers for motor development, we combined DTI with TMS.

MATERIALS AND METHODS: We examined groups of 11 healthy preschool-aged children, 10 healthy adolescents, and 10 healthy adults with both, DTI and TMS/ipsilateral silent period (iSP). DTI-values for fractional anisotropy (FA) were calculated for areas I to V of the CC. ISP-values for latency, duration, and extent of electromyography suppression were calculated.

RESULTS: FA was significantly lower in areas II to IV of the CC in children as compared with adults (P < 0.05). In area III, where callosal motor fibers cross the CC, FA differed significantly between children and adolescents (P < 0.05). TMS parameters demonstrated significant age-related differences in duration and extent of iSP (P < 0.05). No significant differences were detected regarding latency of iSP.

CONCLUSIONS: The maturation of callosal motor fiber connectivity seems to reflect the degree of interhemispheric inhibition between the motor cortices with anisotropy of callosal motor fibers being a potential marker for motor development.