title: Vestibular modulation of muscle sympathetic nerve activity by the utricle during sub-perceptual sinusoidal linear acceleration in humans.
abstract: We assessed the capacity for the vestibular utricle to modulate muscle sympathetic nerve activity (MSNA) during sinusoidal linear acceleration at amplitudes extending from imperceptible to clearly perceptible. Subjects (n = 16) were seated in a sealed room, eliminating visual cues, mounted on a linear motor that could deliver peak sinusoidal accelerations of 30 mG in the antero-posterior direction. Subjects sat on a padded chair with their neck and head supported vertically, thereby minimizing somatosensory cues, facing the direction of motion in the anterior direction. Each block of sinusoidal motion was applied at a time unknown to subjects and in a random order of amplitudes (1.25, 2.5, 5, 10, 20 and 30 mG), at a constant frequency of 0.2 Hz. MSNA was recorded via tungsten microelectrodes inserted into muscle fascicles of the common peroneal nerve. Subjects used a linear potentiometer aligned to the axis of motion to indicate any perceived movement, which was compared with the accelerometer signal of actual room movement. On average, 67% correct detection of movement did not occur until 6.5 mG, with correct knowledge of the direction of movement at ~10 mG. Cross-correlation analysis revealed potent sinusoidal modulation of MSNA even at accelerations subjects could not perceive (1.25-5 mG). The modulation index showed a positive linear increase with acceleration amplitude, such that the modulation was significantly higher (25.3 ± 3.7%) at 30 mG than at 1.25 mG (15.5 ± 1.2%). We conclude that selective activation of the vestibular utricle causes a pronounced modulation of MSNA, even at levels well below perceptual threshold, and provides further evidence in support of the importance of vestibulosympathetic reflexes in human cardiovascular control.
authors: School of Medicine, University of Western Sydney, Locked Bag 1797, Penrith, Sydney, NSW, 2751, Australia.
authors: Elie
authors: E
authors: Hammam
authors: Chui Luen Vera
authors: CL
authors: Hau
authors: Kwok-Shing
authors: KS
authors: Wong
authors: Kenny
authors: K
authors: Kwok
authors: Vaughan G
authors: VG
authors: Macefield
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D010543:Peroneal Nerve / Q000502:physiology*; D012444:Saccule and Utricle / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000502:physiology*; D055815:Young Adult