Modulating motor cortical neuroplasticity with priming paired associative stimulation in young and old adults.
To examine the effect of priming paired associative stimulation (PAS) on the modulation of motor cortex (M1) plasticity in young and old adults.



Fifteen young (20-27yrs) and 15 old (61-79yrs) subjects participated in 3 experimental sessions, with each session involving two consecutive PAS protocols separated by 10mins. The first (priming) protocol was either PASLTP(ISI=N20 latency+2ms), PASLTD(ISI=N20 latency-10ms), or PASControl(ISI=100ms), whereas the second (test) protocol was always PASLTP. Changes in M1 excitability were assessed from motor evoked potentials (MEPs) in a hand muscle.



In young subjects, MEPs were larger after PASLTP+PASLTPthan PASLTD+PASLTP(P<0.0001) and PASControl+PASLTP(P=0.0008), whereas the response to PASControl+PASLTPwas not different to PASLTD+PASLTP(P=0.3). In old subjects, MEPs were smaller after PASLTP+PASLTPcompared with PASControl+PASLTP(P=0.02), whereas PASLTD+PASLTPwas similar to PASControl+PASLTP(P=0.08). Age-related comparisons within each priming condition showed that the response to PASLTP+PASLTPwas significantly greater in young subjects (P=0.03).



Data show that priming with PASLTPwas effective in young but not old subjects.



These findings suggest a limited utility of priming PAS for augmenting plasticity induction in old adults.
Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia.
George M
GM
Opie
Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia; Centre for Human Movement Sciences, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
Aylin K
AK
Post
Robinson Research Institute, School of Medicine, The University of Adelaide, Adelaide, Australia.
Michael C
MC
Ridding
Department of Neurology & Stroke, and Hertie-Institute for Clinical Brain Research, Eberhard Karls University of Tübingen, Tübingen, Germany.
Ulf
U
Ziemann
Discipline of Physiology, School of Medicine, The University of Adelaide, Adelaide, Australia. Electronic address: john.semmler@adelaide.edu.au.
John G
JG
Semmler
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D001244:Association; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000254:growth & development / Q000502:physiology*; D009473:Neuronal Plasticity; D060865:Repetition Priming
Ageing; Metaplasticity; Neuroplasticity; Paired-associative stimulation; Primary motor cortex; Transcranial magnetic stimulation