Postural control and vestibulospinal function in patients selected for cochlear implantation.

Postural control, vestibular and eye motor function were evaluated in seven postlingually deaf patients before cochlear implantation and were compared with 21 control subjects. Vibration to the calf muscles or galvanic electrical stimulation of the vestibular nerves, perturbed stance and body sway velocity, statistical variance of antero-posterior body sway and identification of characteristic parameters of postural dynamics were all evaluated. Vibration-induced body sway was increased among the patients compared with the normal subjects and there were differences in characteristic parameters of postural dynamics, indicating decreased postural control. Galvanic stimulation induced a body sway not significantly different from the control group suggesting that the patients selected for cochlear implantation, and with an otherwise reduced postural control, are sensitive to electrical stimulation of the vestibular nerve. Thus, postlingually deaf subjects who perceive a sensation of sound at electrical promontorial stimulation also respond with increased body sway to electrical stimulation aimed at the vestibular nerves. This finding may contribute an additional hypothesis to the causes of dizziness among cochlear implant patients, complementary to the that of wrongly placed electrodes and peroperative vestibular lesions.