title: Electrical vestibular stimulation after vestibular deafferentation and in vestibular schwannoma.
abstract: BACKGROUND
  Vestibular reflexes, evoked by human electrical (galvanic) vestibular stimulation (EVS), are utilized to assess vestibular function and investigate its pathways. Our study aimed to investigate the electrically-evoked vestibulo-ocular reflex (eVOR) output after bilateral and unilateral vestibular deafferentations to determine the characteristics for interpreting unilateral lesions such as vestibular schwannomas.
  
  
  METHODS
  EVOR was recorded with dual-search coils as binocular three-dimensional eye movements evoked by bipolar 100 ms-step at EVS intensities of [0.9, 2.5, 5.0, 7.5, 10.0] mA and unipolar 100 ms-step at 5 mA EVS intensity. Five bilateral vestibular deafferented (BVD), 12 unilateral vestibular deafferented (UVD), four unilateral vestibular schwannoma (UVS) patients and 17 healthy subjects were tested with bipolar EVS, and five UVDs with unipolar EVS.
  
  
  RESULTS
  After BVD, bipolar EVS elicited no eVOR. After UVD, bipolar EVS of one functioning ear elicited bidirectional, excitatory eVOR to cathodal EVS with 9 ms latency and inhibitory eVOR to anodal EVS, opposite in direction, at half the amplitude with 12 ms latency, exhibiting an excitatory-inhibitory asymmetry. The eVOR patterns from UVS were consistent with responses from UVD confirming the vestibular loss on the lesion side. Unexpectedly, unipolar EVS of the UVD ear, instead of absent response, evoked one-third the bipolar eVOR while unipolar EVS of the functioning ear evoked half the bipolar response.
  
  
  CONCLUSIONS
  The bidirectional eVOR evoked by bipolar EVS from UVD with an excitatory-inhibitory asymmetry and the 3 ms latency difference between normal and lesion side may be useful for detecting vestibular lesions such as UVS. We suggest that current spread could account for the small eVOR to 5 mA unipolar EVS of the UVD ear.
authors.affiliation: Central Clinical School, University of Sydney, Sydney, Australia ; Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Swee Tin
authors.initials: ST
authors.lastname: Aw
authors.affiliation: Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Michael John
authors.initials: MJ
authors.lastname: Todd
authors.affiliation: Neurology, Ludwig-Maximilians University, German Centre for Vertigo and Balance Disorders, Munich, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Lehnen
authors.affiliation: Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Grace Elizabeth
authors.initials: GE
authors.lastname: Aw
authors.affiliation: Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Konrad Peter
authors.initials: KP
authors.lastname: Weber
authors.affiliation: Neurology, Ludwig-Maximilians University, German Centre for Vertigo and Balance Disorders, Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Eggert
authors.affiliation: Central Clinical School, University of Sydney, Sydney, Australia ; Institute of Clinical Neuroscience, Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Gabor Michael
authors.initials: GM
authors.lastname: Halmagyi
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000473:pathology; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D004558:Electric Stimulation; D004599:Electric Stimulation Therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000473:pathology* / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D013997:Time Factors; D014722:Vestibule, Labyrinth / Q000294:innervation* / Q000473:pathology* / Q000503:physiopathology