title: Older adults exhibit more intracortical inhibition and less intracortical facilitation than young adults.
abstract: BACKGROUND
  Aging results in decreased neuromuscular function, which is likely associated with neurologic alterations. At present little is known regarding age-related changes in intracortical properties.
  
  
  METHODS
  In this study we used transcranial magnetic stimulation (TMS) to measure intracortical facilitation (ICF), short- and long-interval intracortical inhibition (SICI and LICI), motor evoked potential amplitude, and silent period duration in young and older adults (21.4+/-0.8years and 70.9+/-1.8years). These variables were assessed from the flexor carpi radialis muscle of the non-dominant arm under resting conditions, and during a submaximal contraction (intensity 15% maximum strength).
  
  
  RESULTS
  Older adults exhibited increased SICI and LICI in comparison to young adults (SICI: 29.0+/-9.2% vs. 46.2+/-4.8% of unconditioned pulse; LICI: 6.5+/-1.7% vs. 15.8+/-3.3% of unconditioned pulse; P=0.04), and less ICF under resting conditions (74.6+/-8.7% vs. 104.9+/-6.9% of unconditioned pulse; P=0.02). These age-related differences disappeared during contraction, although the older adults did exhibit a longer silent period during contraction (112.5+/-6.5 vs. 84.0+/-3.9ms; P<0.01).
  
  
  CONCLUSIONS
  Collectively, these findings suggest increased GABA mediated intracortical inhibition with age.
authors.affiliation: Institute for Neuromusculoskeletal Research, Ohio University, United States; Department of Biomedical Sciences, Ohio University, United States.
authors.forename: Marisa
authors.initials: M
authors.lastname: McGinley
authors.forename: Richard L
authors.initials: RL
authors.lastname: Hoffman
authors.forename: David W
authors.initials: DW
authors.lastname: Russ
authors.forename: James S
authors.initials: JS
authors.lastname: Thomas
authors.forename: Brian C
authors.initials: BC
authors.lastname: Clark
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000368:Aged; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009044:Motor Cortex / Q000254:growth & development* / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D014955:Wrist Joint / Q000254:growth & development / Q000502:physiology; D055815:Young Adult