title: Increased intracortical inhibition in elderly adults with anterior-posterior current flow: A TMS study.
abstract: OBJECTIVE
  All previous studies using TMS to assess short-interval intracortical inhibition (SICI) in older adults have used a conventional coil orientation, which produces posterior-to-anterior (PA) current flow in the motor cortex. However, no studies have examined SICI in older adults by reversing the coil to induce anterior-to-posterior (AP) current flow, which is considered more sensitive at detecting SICI. Therefore, we investigated age-related changes in SICI using both PA and AP TMS across different conditioning stimulus intensities and muscle activation states.
  
  
  METHODS
  In 22 young and 20 older adults, SICI was assessed using PA and AP coil orientations, across a range of conditioning stimulus intensities (70-90% active motor threshold), and whilst participants kept their first dorsal interosseous (FDI) muscle either relaxed or active (2N force).
  
  
  RESULTS
  There were no age-related differences in SICI using conventional PA TMS in resting or active FDI muscle. However, SICI was increased in elderly participants when assessed with reverse coil AP TMS in resting FDI.
  
  
  CONCLUSIONS
  Coil orientation is a key factor to consider when assessing age-related differences in SICI.
  
  
  CONCLUSIONS
  Reverse coil AP TMS can reveal age-related changes in SICI, which were previously not evident with conventional PA TMS. This may have implications for the assessment of SICI in some clinical populations that may show subtle differences in SICI circuitry.
authors.affiliation: Queensland Brain Institute, The University of Queensland, St Lucia, QLD 4072, Australia.
authors.forename: Martin V
authors.initials: MV
authors.lastname: Sale
authors.affiliation: School of Physiotherapy and Exercise Science, Curtin University, Bentley, WA 6102, Australia.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Lavender
authors.affiliation: Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.
authors.forename: George M
authors.initials: GM
authors.lastname: Opie
authors.affiliation: Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Nordstrom
authors.affiliation: Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia. Electronic address: john.semmler@adelaide.edu.au.
authors.forename: John G
authors.initials: JG
authors.lastname: Semmler
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult
keywords: Ageing; Intracortical inhibition; Motor cortex; Movement control; Transcranial magnetic stimulation