title: TMS-evoked silent periods in scalene and parasternal intercostal muscles during voluntary breathing.
abstract: Transcranial magnetic stimulation (TMS) during voluntary muscle contraction causes a period of reduced electromyographic (EMG) activity (EMG). This is attributed to cortical inhibition and is known as the 'silent period'. Silent periods were compared in inspiratory muscles following TMS during voluntary inspiratory efforts during normocapnia, hypercapnia, and hypocapnia. TMS was delivered during isometric and dynamic contractions of scalenes and parasternal intercostals at 25% maximum inspiratory pressure. Changing end-tidal CO2 did not affect the duration of the silent period nor suppression of EMG activity during the silent period. In scalenes, silent periods were shorter for dynamic compared to isometric contractions (p<0.05); but contraction type did not alter the degree of suppression of EMG during the silent period. In parasternal intercostal, no significant differences in silent period parameters occurred for the different contraction types. The lack of effect of end-tidal CO2 suggests that descending drive from the medullary respiratory centres does not independently activate the inspiratory muscles during voluntary inspiratory efforts.
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick 2031, NSW, Australia; The University of New South Wales, Sydney 2052, NSW, Australia.
authors.forename: Billy L
authors.initials: BL
authors.lastname: Luu
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick 2031, NSW, Australia; The University of New South Wales, Sydney 2052, NSW, Australia.
authors.forename: Julian P
authors.initials: JP
authors.lastname: Saboisky
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick 2031, NSW, Australia; The University of New South Wales, Sydney 2052, NSW, Australia.
authors.forename: Janet L
authors.initials: JL
authors.lastname: Taylor
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick 2031, NSW, Australia; The University of New South Wales, Sydney 2052, NSW, Australia.
authors.forename: Simon C
authors.initials: SC
authors.lastname: Gandevia
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick 2031, NSW, Australia; The University of New South Wales, Sydney 2052, NSW, Australia. Electronic address: j.butler@neura.edu.au.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Butler
mesh_terms: D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007366:Intercostal Muscles / Q000502:physiology*; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D012119:Respiration; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Cortical; Drive; Hypercapnia; Inhibition; Magnetic stimulation; Respiratory