title: Threshold tracking transcranial magnetic stimulation: Effects of age and gender on motor cortical function.
abstract: Recently, the utility of threshold tracking paired-pulse transcranial magnetic stimulation (TTTMS), to measure changes in cortical excitabilitability, has been established for diagnostic purposes across a range of neurological diseases. However, the impact of healthy aging on the GABA-ergic intracortical inhibitory system remains unclear. To improve the clinical applicability, TTTMS was performed across an age spectrum.
  
  
  
  TTTMS, single-pulse TMS and nerve conduction studies (NCS) were performed in 113 healthy subjects aged between 20 and 83years (57 male and 56 female).
  
  
  
  Prolonged motor evoked potential (MEP) latency, increased central motor conduction time, decreased compound muscle action potential (CMAP) amplitude, prolonged F-wave latency and decreased neurophysiological index (NI), calculated from CMAP amplitude, latency and F-wave frequency, were observed as subjects aged. In contrast, short interval intracortical inhibition (SICI) and facilitation did not change. Compared to females, males exhibited a reduced SICI and NI along with longer MEP, CMAP with prolonged F-wave latencies. Multivariate analyses revealed similar results.
  
  
  
  Utilizing clinically applicable TTTMS protocols, findings suggest that GABA mediated intracortical inhibition may be greater in females but does not significantly change with age.
  
  
  
  These findings may better inform the interpretation of diagnostic TTTMS studies in the clinical setting.
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia.
authors.forename: Kazumoto
authors.initials: K
authors.lastname: Shibuya
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia.
authors.forename: Susanna B
authors.initials: SB
authors.lastname: Park
authors.affiliation: Western Clinical School, University of Sydney, Sydney, NSW 2145, Australia.
authors.forename: Nimeshan
authors.initials: N
authors.lastname: Geevasinga
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia.
authors.forename: William
authors.initials: W
authors.lastname: Huynh
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia.
authors.forename: Neil G
authors.initials: NG
authors.lastname: Simon
authors.affiliation: Western Clinical School, University of Sydney, Sydney, NSW 2145, Australia.
authors.forename: Parvathi
authors.initials: P
authors.lastname: Menon
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Howells
authors.affiliation: Western Clinical School, University of Sydney, Sydney, NSW 2145, Australia.
authors.forename: Steve
authors.initials: S
authors.lastname: Vucic
authors.affiliation: Brain and Mind Centre, Sydney Medical School, University of Sydney, Sydney, NSW 2050, Australia. Electronic address: matthew.kiernan@sydney.edu.au.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Kiernan
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000254:growth & development / Q000502:physiology*; D012737:Sex Factors; D050781:Transcranial Magnetic Stimulation
keywords: Age-related change; Cortex function; Gender-related difference; Healthy subject; Intracortical inhibition; Threshold tracking transcranial magnetic stimulation