title: Single motor unit responses underlying cervical vestibular evoked myogenic potentials produced by bone-conducted stimuli.
abstract: OBJECTIVE
  Cervical vestibular evoked myogenic potentials (cVEMPs) are muscle reflexes recorded from the sternocleidomastoid (SCM) neck muscles following vestibular activation with air- or bone-conducted (BC) stimulation. We investigated the effect of different forms of BC stimulation on the single motor unit response underlying the cVEMP.
  
  
  METHODS
  We tested 8 healthy human subjects with 5 different stimuli. Motor units were recorded with thin concentric needle electrodes; surface potentials were recorded simultaneously.
  
  
  RESULTS
  The polarity of the initial change (at approx. 15 ms) in single motor unit activity reflected the polarity of the surface cVEMPs: a short-latency decrease in activity (inhibition) was seen with the four stimuli that produced a positive surface potential (p13), while an initial increase in activity (excitation) was seen with the stimulus that produced a negative surface potential.
  
  
  CONCLUSIONS
  BC stimulation with common clinical stimuli usually produces an inhibition in single motor unit activity in the ipsilateral SCM muscle. However the projections activated by BC stimulation are not exclusively inhibitory in nature and depend upon the shape and direction of the stimulus.
  
  
  CONCLUSIONS
  The utricle is likely to contribute to some BC cVEMPs, as some stimuli clearly evoke an excitation that is not likely to be saccular in origin.
authors.affiliation: Neurology Department, Royal Prince Alfred Hospital, Sydney, Australia; Central Clinical School, University of Sydney, Australia. Electronic address: sally@srosengren.org.
authors.forename: Sally M
authors.initials: SM
authors.lastname: Rosengren
authors.affiliation: Prince of Wales Clinical School and Medical Research Institute, University of New South Wales, Sydney, Australia.
authors.forename: James G
authors.initials: JG
authors.lastname: Colebatch
authors.affiliation: Neurology Department, University Hospital Zurich, Switzerland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Straumann
authors.affiliation: Neurology Department, University Hospital Zurich, Switzerland; Ophthalmology Department, University Hospital Zurich, Switzerland.
authors.forename: Konrad P
authors.initials: KP
authors.lastname: Weber
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods*; D000328:Adult; D001844:Bone Conduction / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009334:Neck Muscles / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012444:Saccule and Utricle / Q000502:physiology; D058585:Vestibular Evoked Myogenic Potentials / Q000502:physiology*; D014722:Vestibule, Labyrinth / Q000502:physiology; D055815:Young Adult
keywords: Bone conduction; Otolith; Single motor unit; Sternocleidomastoid muscle; VEMP; Vestibular evoked myogenic potential; Vibration