title: Skull tap induced vestibular evoked myogenic potentials: an ipsilateral vibration response and a bilateral head acceleration response?
abstract: OBJECTIVE
  To explore the mechanisms for skull tap induced vestibular evoked myogenic potentials (VEMP).
  
  
  METHODS
  An electro-mechanical "skull tapper" (that provided a constant stimulus intensity) was used to test the effects of different midline stimulus sites/directions in healthy subjects (n=10) and in patients with severe unilateral loss of vestibular function (n=8).
  
  
  RESULTS
  The standardized midline skull taps caused highly reproducible VEMP. There were highly significant differences in amplitude and latency in both normals and patients depending on site/direction of tapping (suggesting a stimulus direction dependency). Occiput skull taps caused, in comparisons to forehead and vertex taps, larger amplitude VEMP with more pronounced differences between the lesioned and the healthy side in the patients.
  
  
  CONCLUSIONS
  The present data, in conjunction with earlier findings, support a theory that skull tap VEMP are mediated by two different mechanisms. It is suggested that skull tapping causes both skull vibration and head acceleration. Further, the VEMP would be the sum of the direction-independent vibration-induced response (from the sound-sensitive part of the saccule) and the direction-dependent head acceleration response (from other parts of the labyrinth).
  
  
  CONCLUSIONS
  Skull tap VEMP, as a diagnostic test, is not equivalent to sound-induced VEMP.
authors.affiliation: Department of Audiology, Karolinska Hospital, 171 76 Stockholm, Sweden. krister.brantberg@karolinska.se
authors.forename: Krister
authors.initials: K
authors.lastname: Brantberg
authors.forename: Lennart
authors.initials: L
authors.lastname: Löfqvist
authors.forename: Magnus
authors.initials: M
authors.lastname: Westin
authors.forename: Arne
authors.initials: A
authors.lastname: Tribukait