title: Age-related differences in short- and long-interval intracortical inhibition in a human hand muscle.
abstract: BACKGROUND
  Effects of age on the assessment of intracortical inhibition with paired-pulse transcranial magnetic stimulation (TMS) have been variable, which may be due to between-study differences in test TMS intensity and test motor evoked potential (MEP) amplitude.
  
  
  OBJECTIVE
  To investigate age-related differences in short- (SICI) and long-interval intracortical inhibition (LICI) across a range of test TMS intensities and test MEP amplitudes.
  
  
  METHODS
  In 22 young and 18 older subjects, SICI and LICI were recorded at a range of test TMS intensities (110%-150% of motor threshold) while the first dorsal interosseous (FDI) muscle was at rest, or producing a precision grip of the index finger and thumb. Data were subsequently compared according to the amplitude of the MEP produced by the test alone TMS.
  
  
  RESULTS
  When pooled across all test TMS intensities, SICI in resting muscle and LICI in active muscle were similar in young and older adults, whereas SICI in active muscle and LICI in resting muscle were reduced in older adults. Regrouping data based on test MEP amplitude demonstrated similar effects of age for SICI and LICI in resting muscle, whereas more subtle differences between age groups were revealed for SICI and LICI in active muscle.
  
  
  CONCLUSIONS
  Advancing age influences GABA-mediated intracortical inhibition, but the outcome is dependent on the experimental conditions. Age-related differences in SICI and LICI were influenced by test TMS intensity and test MEP amplitude, suggesting that these are important considerations when assessing intracortical inhibition in older adults, particularly in an active muscle.
authors.affiliation: Discipline of Physiology, School of Medical Sciences, The University of Adelaide, Adelaide, South Australia 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, South Australia 5005, Australia. Electronic address: john.semmler@adelaide.edu.au.
authors.forename: John G
authors.initials: JG
authors.lastname: Semmler
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006225:Hand / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D012146:Rest / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Gamma-aminobutyric acid; Motor evoked potential; Muscle activation; Paired-pulse TMS; Transcranial magnetic stimulation