Normal summating potential to tone bursts recorded from the tympanic membrane in humans.

The use of tone-burst stimuli for electrocochleography (ECochG) may offer certain advantages over conventional broad-band clicks. Namely, the summating potential (SP) component can be examined at different frequencies and may be easier to define and measure. To apply these findings clinically, it would first be necessary to establish SP amplitudes as a function of tone-burst frequency in normal listeners. The purpose of the present study was to do this using the tympanic membrane (TM) as the primary ECochG recording site. ECochG was recorded from 20 normal ears. Stimuli included 500-, 1000-, 2000-, 4000-, and 8000-Hz tone bursts presented randomly at 90 dB nHL. Mean SP amplitudes at these frequencies were +0.19, +0.17, +0.08, +0.10, and +0.22 microvolts, respectively. Although mean amplitudes were slightly positive regarding baseline, individual amplitudes varied between -0.41 and +0.73 microvolts. This study offers additional evidence that the SP to tone bursts can be recorded from the TM. The normative data provided should be useful for extended studies involving clinical populations.

Human summating potential to tone bursts: observations on tympanic membrane versus promontory recordings in the same patients.

Electrocochleographic responses to tone bursts and clicks were recorded from the tympanic membranes (TMs) and promontories of six suspected Meniere's patients. Although the majority of ears had normal summating potentials (SPs), regardless of recording site and stimulus type, some displayed amplitude-enlarged SPs at both sites and to both types of stimuli. The following observations were made from these patients regarding the choice of recording approaches and stimuli for ECochG: (1) Although SP amplitudes at the promontory were approximately four times larger than corresponding TM values, response "patterns" leading to diagnostic interpretation were the same at both sites; (2) the majority of patients who displayed enlarged SP amplitudes to tone bursts also had enlarged SPs to clicks; and (3) with tone-burst stimuli, the amplitude of the SP alone was sufficient for diagnostic interpretation of the ECochG waveform.

Clinical correlates of sudden auditory-vestibular loss in a cochlear implant patient.

The precise electrophysiologic mechanism for sudden sensorineural auditory-vestibular loss has yet to be defined. No human models exist for this idiopathic phenomenon. A 67-year-old cochlear implant (CI) patient experienced what could be termed a "typical" acute sudden auditory-vestibular loss. Vestibular and CI electrical psychophysical changes were monitored over a 22-month period. Once the acute vestibular problems diminished, CI electrical parameters returned to near pre-episode levels. Some improvement occurred in rotational chair phase lag and asymmetry. While improving, platform posturography continued to show difficulty performing sensory organization tests V and VI. These clinical findings may imply that ganglion cell and neuronal population are responsible for the auditory findings in sudden auditory-vestibular loss. Secondly, a CI patient may serve as an ideal human model for further study of this phenomenon, should it occur.

Feasibility of multichannel human cochlear nucleus stimulation.

Bipolar electrical stimulation of the brainstem cochlear nucleus (CN) following acoustic tumor removal in an only-hearing ear can provide beneficial hearing. However, the benefits of multichannel stimulation have yet to be defined. Following removal of a second acoustic tumor in a patient with neurofibromatosis 2, a Nucleus mini-22 channel implant device was inserted with the electrode array tip from the foramen of Luschka cephalad along the root entry zone of the eighth nerve, secured by a single suture superficially in the brain stem. Initial stimulation on the sixth postoperative day indicated that electrodes 18 to 22 were capable of CN stimulation without seventh nerve stimulation. Presumed electrode migration precluded further CN stimulation 1 month later. This report illustrates the feasibility of brainstem CN stimulation with an existing multichannel system.