title: Age-related Differences in Pre- and Post-synaptic Motor Cortex Inhibition are Task Dependent.
abstract: BACKGROUND
  Previous research has shown age-related differences in short- (SICI) and long-interval intracortical inhibition (LICI) in both resting and active hand muscles, suggesting that healthy ageing influences post-synaptic motor cortex inhibition. However, it is not known how the ageing process effects the pre-synaptic interaction of SICI by LICI, and how these pre- and post-synaptic intracortical inhibitory circuits are modulated by the performance of different motor tasks in older adults.
  
  
  OBJECTIVE
  To examine age-related differences in pre- and post-synaptic motor cortex inhibition at rest, and during index finger abduction and precision grip.
  
  
  METHODS
  In 13 young (22.3 ± 3.8 years) and 15 old (73.7 ± 4.0 years) adults, paired-pulse transcranial magnetic stimulation (TMS) was used to measure SICI (2 ms inter-stimulus interval; ISI) and LICI (100 and 150 ms ISI), whereas triple-pulse TMS was used to investigate SICI when primed by LICI.
  
  
  RESULTS
  We found no age-related difference in SICI at rest or during index finger abduction, but significantly greater SICI in older subjects during precision grip. Older adults showed reduced LICI in resting muscle (at an ISI of 150 ms), with no age-related differences in LICI during either task. When SICI was primed by LICI, disinhibition of motor cortex was reduced in older adults at rest (100 ms ISI) and during index finger abduction (150 ms ISI), but not during precision grip.
  
  
  CONCLUSIONS
  Our results support age-related differences in pre- and post-synaptic motor cortex inhibition, which may contribute to impaired hand function during task performance in older adults.
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: Robinson Research Institute, School of Paediatrics and Reproductive Health, The University of Adelaide, Adelaide, Australia.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Ridding
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; D000367:Age Factors; D000368:Aged; D019054:Evoked Potentials, Motor; D005260:Female; D018737:Hand Strength; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000254:growth & development / Q000502:physiology*; D009433:Neural Inhibition; D011597:Psychomotor Performance; D009435:Synaptic Transmission; D050781:Transcranial Magnetic Stimulation
keywords: Age; Gamma-aminobutyric acid; Pre-synaptic inhibition; Task; Transcranial magnetic stimulation