title: Priming theta burst stimulation enhances motor cortex plasticity in young but not old adults.
abstract: Primary motor cortex neuroplasticity is reduced in old adults, which may contribute to the motor deficits commonly observed in the elderly. Previous research in young subjects suggests that the neuroplastic response can be enhanced using non-invasive brain stimulation (NIBS), with a larger plastic response observed following priming with both long-term potentiation (LTP) and depression (LTD)-like protocols. However, it is not known if priming stimulation can also modulate plasticity in older adults.
  
  
  
  To investigate if priming NIBS can be used to modulate motor cortical plasticity in old subjects.
  
  
  
  In 16 young (22.3 ± 1.0 years) and 16 old (70.2 ± 1.7 years) subjects, we investigated the response to intermittent theta burst stimulation (iTBS; LTP-like) when applied 10 min after sham stimulation, continuous TBS (cTBS; LTD-like) or an identical block of iTBS. Corticospinal plasticity was assessed by recording changes in motor evoked potential (MEP) amplitude.
  
  
  
  In young subjects, priming with cTBS (cTBS + iTBS) resulted in larger MEPs than priming with either iTBS (iTBS + iTBS; P = 0.001) or sham (sham + iTBS; P < 0.0001), while larger MEPs were seen following iTBS + iTBS than sham + iTBS (P < 0.0001). In old subjects, the response to iTBS + iTBS was not different to sham + iTBS (P > 0.9), whereas the response to cTBS + iTBS was reduced relative to iTBS + iTBS (P = 0.02) and sham + iTBS (P = 0.04).
  
  
  
  Priming TBS is ineffective for modifying M1 plasticity in older adults, which may limit the therapeutic use of priming stimulation in neurological conditions common in the elderly.
authors.affiliation: Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia.
authors.forename: George M
authors.initials: GM
authors.lastname: Opie
authors.affiliation: Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia.
authors.forename: Eleni
authors.initials: E
authors.lastname: Vosnakis
authors.affiliation: Robinson Research Institute, School of Medicine, The University of Adelaide, Adelaide, Australia.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Ridding
authors.affiliation: Department of Neurology & Stroke, Hertie-Institute for Clinical Brain Research, Eberhard Karls University of Tübingen, Tübingen, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Ziemann
authors.affiliation: Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia. Electronic address: john.semmler@adelaide.edu.au.
authors.forename: John G
authors.initials: JG
authors.lastname: Semmler
mesh_terms: D000367:Age Factors; D000368:Aged; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D017774:Long-Term Potentiation / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D019635:Neurosurgical Procedures; D013238:Stereotaxic Techniques; D013826:Theta Rhythm / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Ageing; Metaplasticity; Priming; Theta burst stimulation; Transcranial magnetic stimulation