Neuropediatrics 2005; 36 - P112
DOI: 10.1055/s-2005-868097

Development of transcallosal inhibition after focal magnetic stimulation in children: a longitudinal study

S Armbruster 1, C Haberl 1, M Walter 2, G Gallistl 1, F Heinen 1
  • 1Dr. von Haunersches Kinderspital der LMU, Abt. für pädiatrische Neurologie und Entwicklungsneurologie, München
  • 2Universitätskinderklinik, Abt. Neuropädiatrie und Muskelerkrankungen, Freiburg

Objectives: Transcranial Magnetic Stimulation (TMS) of the motor cortex evokes a transcallosal inhibition (TI) of the EMG in the corresponding ipsilateral muscle. There is strong evidence that TI depends on transcallosal pathways of the corpus callosum. Preschool children had no detectable TI at the age of 4.6 years. To find out more about the course of age-dependent TI development, we now re-examined the same children several years later.

Material and Methods: Six healthy right-handed children (mean age: 12.5 years) were studied. The surface EMG was recorded from the right and left first dorsal interosseus muscle (FDI). Focal TMS was performed over the hand area of the left motor cortex with a figure of 8-coil. Motor evoked potentials (MEP), active motor thresholds (AMT) and TI were measured. In addition we performed a standardized neurologic examination including mirror movements.

Results: Following TMS, functional TI of the ongoing EMG was detected in all 6 children. None of the children showed ipsilateral muscle evoked potentials. The AMT showed a longitudinal decrease from 80% at the age of 4.6 years to 40% at the age of 12.5 years. None of the children showed significant mirror movements in several motor performance tasks.

Conclusions: TI, which was not detectable at the age of 4.6 years, could be measured in all examined children at the age of 12.5 years. We observed an age-related development of TI.

During the same time period, all children learned to perform dissociated and isolated hand and finger movements with absence of mirror movements. Disappearance of mirror movements is thought to be related to the maturation of transcallosal pathways. Our data suggest an association between maturation of neuromotor skills and development of neurophysiological findings.

The development of TI may reflect morphologic structural as well as functional maturation of the corpus callosum. To investigate the structural changes of interhemispheric pathways in the corpus callosum we additionally performed MRI with diffusion tensor imaging in all children.