title: Primary motor cortical metaplasticity induced by priming over the supplementary motor area.
abstract: Motor cortical plasticity induced by repetitive transcranial magnetic stimulation (rTMS) sometimes depends on the prior history of neuronal activity. These effects of preceding stimulation on subsequent rTMS-induced plasticity have been suggested to share a similar mechanism to that of metaplasticity, a homeostatic regulation of synaptic plasticity. To explore metaplasticity in humans, many investigations have used designs in which both priming and conditioning are applied over the primary motor cortex (M1), but the effects of priming stimulation over other motor-related cortical areas have not been well documented. Since the supplementary motor area (SMA) has anatomical and functional cortico-cortical connections with M1, here we studied the homeostatic effects of priming stimulation over the SMA on subsequent rTMS-induced plasticity of M1. For priming and subsequent conditioning, we employed a new rTMS protocol, quadripulse stimulation (QPS), which produces a broad range of motor cortical plasticity depending on the interval of the pulses within a burst. The plastic changes induced by QPS at various intervals were altered by priming stimulation over the SMA, which did not change motor-evoked potential sizes on its own but specifically modulated the excitatory I-wave circuits. The data support the view that the homeostatic changes are mediated via mechanisms of metaplasticity and highlight an important interplay between M1 and SMA regarding homeostatic plasticity in humans.
authors.affiliation: Department of Neurology, Division of Neuroscience, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. mhamada-tky@umin.net
authors.forename: Masashi
authors.initials: M
authors.lastname: Hamada
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hanajima
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Terao
authors.forename: Shingo
authors.initials: S
authors.lastname: Okabe
authors.forename: Setsu
authors.initials: S
authors.lastname: Nakatani-Enomoto
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Shirota
authors.forename: Shinya
authors.initials: S
authors.lastname: Ohminami
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ugawa
mesh_terms: D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006706:Homeostasis; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009433:Neural Inhibition; D009473:Neuronal Plasticity; D050781:Transcranial Magnetic Stimulation / Q000379:methods