title: The influence of short-interval intracortical facilitation when assessing developmental changes in short-interval intracortical inhibition.
abstract: OBJECTIVE
  Measures of short-interval intracortical inhibition (SICI) can be contaminated by excitatory influences of short-interval intracortical facilitation (SICF), unless examined at individually-optimized interstimulus intervals (ISIs). We hypothesized that age-related differences in SICF would explain previously reported reduced SICI in children and adolescents compared with adults.
  
  
  METHODS
  Fifty-one participants, aged 8-29years, underwent transcranial magnetic stimulation. SICF curves were constructed to determine the ISI at which SICF was minimal (i.e. the first trough). SICI curves were constructed at this individually-determined ISI with conditioning stimulus (S1) intensities of 60-110% of active motor threshold.
  
  
  RESULTS
  There was no effect of age on the ISI corresponding with the SICF trough. However, there was a main effect of age on the amplitude of the conditioned motor-evoked potential at the different ISIs, such that children aged 8-12years demonstrated greater SICF than those aged 16-18 and 19-21years. There was no effect of age on SICI, and no interaction between age group and S1 intensity.
  
  
  CONCLUSIONS
  Compared with that in older adolescents and young adults, SICF is enhanced in children aged 8-12years. Surprisingly, this enhanced SICF does not appear to reduce the degree of SICI that can be evoked at the first trough in this age group.
  
  
  CONCLUSIONS
  This is the first report of enhanced SICF in young children. It remains possible that enhanced SICF may have confounded earlier reports of reduced SICI in children less than 8years.
authors.affiliation: Robinson Research Institute, Paediatrics & Reproductive Health, School of Medicine, University of Adelaide, Adelaide 5005, Australia.
authors.forename: L A
authors.initials: LA
authors.lastname: Schneider
authors.affiliation: Robinson Research Institute, Paediatrics & Reproductive Health, School of Medicine, University of Adelaide, Adelaide 5005, Australia.
authors.forename: M R
authors.initials: MR
authors.lastname: Goldsworthy
authors.affiliation: Robinson Research Institute, Paediatrics & Reproductive Health, School of Medicine, University of Adelaide, Adelaide 5005, Australia.
authors.forename: J P
authors.initials: JP
authors.lastname: Cole
authors.affiliation: Robinson Research Institute, Paediatrics & Reproductive Health, School of Medicine, University of Adelaide, Adelaide 5005, Australia.
authors.forename: M C
authors.initials: MC
authors.lastname: Ridding
authors.affiliation: Robinson Research Institute, Paediatrics & Reproductive Health, School of Medicine, University of Adelaide, Adelaide 5005, Australia. Electronic address: julia.pitcher@adelaide.edu.au.
authors.forename: J B
authors.initials: JB
authors.lastname: Pitcher
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002657:Child Development / Q000502:physiology*; D003213:Conditioning, Psychological / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: children; gamma-aminobutyric acid; motor-evoked potential; paired-pulse TMS; transcranial magnetic stimulation