title: The supplementary motor area exerts a tonic excitatory influence on corticospinal projections to phrenic motoneurons in awake humans.
abstract: BACKGROUND
  In humans, cortical mechanisms can interfere with autonomic breathing. Respiratory-related activation of the supplementary motor area (SMA) has been documented during voluntary breathing and in response to inspiratory constraints. The SMA could therefore participate in the increased resting state of the respiratory motor system during wake (i.e. "wakefulness drive to breathe").
  
  
  METHODS
  The SMA was conditioned by continuous theta burst magnetic stimulation (cTBS, inhibitory) and 5 Hz conventional rTMS (5 Hz, excitatory). The ensuing effects were described in terms of the diaphragm motor evoked response (DiMEPs) to single-pulse transcranial magnetic stimulation over the motor cortex. DiMEPs were recorded at baseline, and at 3 time-points ("post1", "post2", "post3") up to 15 minutes following conditioning of the SMA.
  
  
  RESULTS
  cTBS reduced the amplitude of DiMEPs from 327.5 ± 159.8 µV at baseline to 243.3 ± 118.7 µV, 217.8 ± 102.9 µV and 240.6 ± 123.9 µV at post 1, post 2 and post 3, respectively (F = 6.341, p = 0.002). 5 Hz conditioning increased the amplitude of DiMEPs from 184.7 ± 96.5 µV at baseline to 270.7 ± 135.4 µV at post 3 (F = 4.844, p = 0.009).
  
  
  CONCLUSIONS
  The corticospinal pathway to the diaphragm can be modulated in both directions by conditioning the SMA. This suggests that the baseline respiratory activity of the SMA represents an equipoise from which it is possible to move in either direction. The resting corticofugal outflow from the SMA to phrenic motoneurones that this study evidences could putatively contribute to the wakefulness drive to breathe.
authors.affiliation: Université Paris 6, ER10UPMC, Paris, France.
authors.forename: Louis
authors.initials: L
authors.lastname: Laviolette
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Niérat
authors.forename: Anna L
authors.initials: AL
authors.lastname: Hudson
authors.forename: Mathieu
authors.initials: M
authors.lastname: Raux
authors.forename: Etienne
authors.initials: E
authors.lastname: Allard
authors.forename: Thomas
authors.initials: T
authors.lastname: Similowski
mesh_terms: D019054:Evoked Potentials, Motor / Q000502:physiology; D006801:Humans; D009044:Motor Cortex / Q000502:physiology*; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D050781:Transcranial Magnetic Stimulation; D014851:Wakefulness / Q000502:physiology