TY - JOUR
T1 - Transmastoid galvanic stimulation does not affect the vergence-mediated gain increase of the human angular vestibulo-ocular reflex
AU - Migliaccio, Americo A.
AU - Della Santina, Charles C.
AU - Carey, John P.
N1 - Funding Information:
Acknowledgments A.A. Migliaccio was supported by an NHRMRC (Australia) Biomedical CDA 568736 grant and a NIH/ NIDCD (USA) R03 DC007346 grant. C.C Della Santina and J.P. Carey were supported by NIH/NIDCD grants RO1 DC009255 and R01 DC05040, respectively.
PY - 2013/2
Y1 - 2013/2
N2 - Vergence is one of several viewing contexts that require an increase in the angular vestibular-ocular reflex (aVOR) response. A previous monkey study found that the vergence-mediated gain (eye/head velocity) increase of the aVOR was attenuated by 64 % when anodic currents, which preferentially lower the activity of irregularly firing vestibular afferents, were delivered to both labyrinths. We sought to determine whether there was similar evidence implicating a role for irregular afferents in the vergence-mediated gain increase of the human aVOR. Our study is based upon analysis of the aVOR evoked by head rotations, delivered passively while subjects viewed a near (15 cm) or far (124 cm) target and applying galvanic vestibular stimulation (GVS) via surface electrodes. We tested 12 subjects during 2-3 sessions each. Vestibular stimuli consisted of passive whole-body rotations (sinusoids from 0.05-3 Hz and 12-25 /s, and transients with peak ∼15, 50 /s, 500 /s2) and head-on-body impulses (peak ∼30, 150 /s, 3,000 /s2). GVS was on for 10 s every 20 s. All polarity combinations were tested, with emphasis on uni- and bi-lateral anodic inhibition. The average stimulus current was 5.9 ± 1.6 mA (range: 3-9.5 mA), vergence angle (during near viewing) was 22.6 ± 2.8 and slow-phase eye velocity caused by left anodic current stimulation with head stationary was -3.4 ± 1.1 /s, -0.2 ± 0.6 /s and 2.5 ± 1.4 /s (torsion, vertical, horizontal). No statistically significant GVS effects were observed, suggesting that surface electrode GVS has no effect on the vergence-mediated gain increase of the aVOR at the current levels (∼6 mA) tolerated by most humans. We conclude that clinically practical transmastoid GVS does not effectively silence irregular afferents and hypothesize that currents >10 mA are needed to reproduce the monkey results.
AB - Vergence is one of several viewing contexts that require an increase in the angular vestibular-ocular reflex (aVOR) response. A previous monkey study found that the vergence-mediated gain (eye/head velocity) increase of the aVOR was attenuated by 64 % when anodic currents, which preferentially lower the activity of irregularly firing vestibular afferents, were delivered to both labyrinths. We sought to determine whether there was similar evidence implicating a role for irregular afferents in the vergence-mediated gain increase of the human aVOR. Our study is based upon analysis of the aVOR evoked by head rotations, delivered passively while subjects viewed a near (15 cm) or far (124 cm) target and applying galvanic vestibular stimulation (GVS) via surface electrodes. We tested 12 subjects during 2-3 sessions each. Vestibular stimuli consisted of passive whole-body rotations (sinusoids from 0.05-3 Hz and 12-25 /s, and transients with peak ∼15, 50 /s, 500 /s2) and head-on-body impulses (peak ∼30, 150 /s, 3,000 /s2). GVS was on for 10 s every 20 s. All polarity combinations were tested, with emphasis on uni- and bi-lateral anodic inhibition. The average stimulus current was 5.9 ± 1.6 mA (range: 3-9.5 mA), vergence angle (during near viewing) was 22.6 ± 2.8 and slow-phase eye velocity caused by left anodic current stimulation with head stationary was -3.4 ± 1.1 /s, -0.2 ± 0.6 /s and 2.5 ± 1.4 /s (torsion, vertical, horizontal). No statistically significant GVS effects were observed, suggesting that surface electrode GVS has no effect on the vergence-mediated gain increase of the aVOR at the current levels (∼6 mA) tolerated by most humans. We conclude that clinically practical transmastoid GVS does not effectively silence irregular afferents and hypothesize that currents >10 mA are needed to reproduce the monkey results.
KW - Irregular vestibular afferents
KW - Transmastoid galvanic stimulation
KW - Vergence
KW - Vestibulo-ocular reflex
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U2 - 10.1007/s00221-012-3330-2
DO - 10.1007/s00221-012-3330-2
M3 - Article
C2 - 23150093
AN - SCOPUS:84873710734
SN - 0014-4819
VL - 224
SP - 489
EP - 499
JO - Experimental Brain Research
JF - Experimental Brain Research
IS - 3
ER -