title: Galvanic ocular vestibular evoked myogenic potentials provide new insight into vestibulo-ocular reflexes and unilateral vestibular loss.
abstract: OBJECTIVE
  Synchronous extraocular muscle activity can be recorded from around the eyes at the beginning of a vestibular-evoked eye movement (ocular vestibular evoked myogenic potentials, OVEMPs). As galvanic vestibular stimulation (GVS) evokes the vestibulo-ocular reflex, we wished to investigate GVS-evoked OVEMPs.
  
  
  METHODS
  We stimulated 10 normals and 6 patients with unilateral vestibular loss (uVL) with bi/unipolar 4 mA, 2 ms current steps at the mastoid. OVEMPs were recorded from electrodes placed superior and inferior to the eyes.
  
  
  RESULTS
  OVEMPs were present beneath both eyes in all normal subjects: an initial positivity ipsilateral to the cathodal electrode (peak latency 9.9 ms, amplitude 1.3 microV) and an initial negativity contralateral to the cathode (8.8 ms, 2.4 microV). In the patients, stimulation of the affected side produced little or no response. Stimulation of the intact side produced only contralateral responses.
  
  
  CONCLUSIONS
  The infra-orbital response is likely produced primarily by the inferior obliques, producing conjugate torsion away from the cathode. The projection to the ipsilateral eye depends upon normal vestibular function on the contralateral side.
  
  
  CONCLUSIONS
  OVEMPs can be evoked by GVS. While bilateral effects are obtained with unilateral stimulation in normals, the primary vestibular pathway to the inferior oblique in humans is crossed.
authors.affiliation: Prince of Wales Clinical School and Medical Research Institute, University of New South Wales, Randwick, Sydney, NSW 2031, Australia. s.rosengren@unsw.edu.au
authors.forename: Sally M
authors.initials: SM
authors.lastname: Rosengren
authors.forename: Peter
authors.initials: P
authors.lastname: Jombik
authors.forename: G Michael
authors.initials: GM
authors.lastname: Halmagyi
authors.forename: James G
authors.initials: JG
authors.lastname: Colebatch
mesh_terms: D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D009334:Neck Muscles / Q000294:innervation / Q000502:physiology* / Q000503:physiopathology; D009434:Neural Pathways / Q000502:physiology; D009801:Oculomotor Muscles / Q000294:innervation / Q000502:physiology* / Q000503:physiopathology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D015837:Vestibular Diseases / Q000175:diagnosis / Q000503:physiopathology*; D014722:Vestibule, Labyrinth / Q000502:physiology* / Q000503:physiopathology; D055815:Young Adult