Galvanic ocular vestibular evoked myogenic potentials provide new insight into vestibulo-ocular reflexes and unilateral vestibular loss.
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.
Rosengren
Sally M
SM
Prince of Wales Clinical School and Medical Research Institute, University of New South Wales, Randwick, Sydney, NSW 2031, Australia. s.rosengren@unsw.edu.au
Jombik
Peter
P
Halmagyi
G Michael
GM
Colebatch
James G
JG
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