title: Maturation of inhibitory and excitatory motor cortex pathways in children.
abstract: OBJECTIVE
  To study intracortical inhibition and facilitation with paired-pulse transcranial magnetic stimulation in children, adolescents and adults.
  
  
  METHODS
  Paired-pulse transcranial magnetic stimulation (interstimulus intervals (ISI): 1, 3, 5, 10 and 20 ms) was applied over the primary motor cortex (M1) in 30 healthy subjects (range 6-30 years, median age 15 years and 8 months, SD 7,9) divided in three groups: adults (>or=18 years), adolescents (> 10 and < 18 years) and children (<or=10 years).
  
  
  RESULTS
  We observed significantly less intracortical inhibition (SICI) in children's M1 compared to that of adults. Adolescents showed significantly less SICI at the 5 ms interval than did adults. No significant differences were apparent in intracortical facilitation (ICF).
  
  
  CONCLUSIONS
  We postulate that, as in adults, the maturing M1 possesses horizontal glutamatergic cross-links that represent the neuronal substrate of excitatory intracortical pathways. GABAergic interneurons, the neuronal substrate of inhibitory intracortical pathways, mature between childhood and adulthood. Reduced GABAergic inhibition may facilitate neuronal plasticity and motor learning in children.
authors.affiliation: Division of Neuropediatrics and Muscular Disorders, Department of Pediatrics and Adolescent Medicine, University of Freiburg, Mathildenstrasse 1, 79106 Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Walther
authors.forename: Steffen
authors.initials: S
authors.lastname: Berweck
authors.forename: Joachim
authors.initials: J
authors.lastname: Schessl
authors.forename: Michaela
authors.initials: M
authors.lastname: Linder-Lucht
authors.forename: Urban M
authors.initials: UM
authors.lastname: Fietzek
authors.forename: Franz X
authors.initials: FX
authors.lastname: Glocker
authors.forename: Florian
authors.initials: F
authors.lastname: Heinen
authors.forename: Volker
authors.initials: V
authors.lastname: Mall