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 CO 2 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 2 suggests that descending drive from the medullary respiratory centres does not independently activate the inspiratory muscles during voluntary inspiratory efforts.