Junichi Matsushima

Electrical stimulation of the auditory nerve in deaf kittens: Effects on cochlear nucleus morphology

The present study examines the effects of long-term electrical stimulation of the auditory nerve on the morphology of neurons in the cochlear nucleus in young, sensorineural deaf animals. Kittens, systemically deafened using kanamycin and ethacrynic acid, received bilateral cochlear implants and were stimulated unilaterally for periods of up to four months. After sacrifice, cross-sectional areas of neuron somata were measured with an image-analysis system and compared using nonparametric statistics. The areas of cell somata within the anteroventral cochlear nucleus (AVCN) on the stimulated side were significantly larger than those of corresponding somata on the control, unstimulated side (P less than 0.001). However, there was no statistically significant difference among dorsal cochlear nucleus (DCN) neurons. These results indicate that long-term electrical stimulation of the auditory nerve can at least partially negate some effects of early postnatal auditory deprivation at the level of the cochlear nucleus.

A portable digital speech-rate converter for hearing impairment

A real-time hand-sized portable device that slows speech speed without changing the pitch is proposed for hearing impairment. By using this device, people can listen to fast speech at a comfortable speed. A combination of solid-state memory recording and real-time digital signal processing with a single chip processor enables this unique function. A simplified pitchsynchronous, time-scale-modification algorithm is proposed to minimize the complexity of the DSP operation. Unlike the traditional algorithm, this dynamic-processing algorithm reduces distortion even when the expansion rate is only just above 1. Seven out of 10 elderly hearing-impaired listeners showed improvement in a sentence recognition test when using speech-rate conversion with the largest expansion rate, although no improvement was observed in a word recognition test. Some subjects who showed large improvement had limited auditory temporal resolution, but the correlation was not significant. The results suggest that, unlike conventional hearing aids, this device can be used to overcome the deterioration of auditory ability by improving the transfer of information from short-term (echoic) memory into a more stable memory trace in the human auditory system.

Proposal of a new method for narrowing and moving the stimulated region of cochlear implants: animal experiment and numerical analysis

The authors have proposed the tripolar electrode stimulation method (TESM) for narrowing the stimulation region and continuously moving the stimulation site for cochlear implants. The TESM stimulates the auditory nerve array using three adjacent electrodes which are selected among the electrodes of an electrode array within the lymphatic fluid. Current is emitted from each of the two lateral electrodes and received by the central electrode. The current received by the central electrode is made equal to the sum of the currents emitted from the lateral electrodes. Here, the authors evaluate whether or not TESM works according to a theory which is based on numerical analysis using an electrical equivalent circuit model of the auditory nerve fibers. In this simulation, the sums of the excited model fibers are compared to the compound action potentials (CAPs) which the authors obtained through animal experiments. To identify the main parameter while maintaining the amplitude of the CAP (the sum of the fired fibers), the authors assumed the presence of some parameters from the radial current density profile. In the case of the width value among the parameters being kept constant, the amplitude of the CAP was almost constant; thus, the number of the fired fibers was also almost constant. The width value equals the distance between the points at which the profile of the radial current density of the electrode array and the line of the radial threshold current density of the electrode array intersect. It is possible to determine the measure of the stimulation region or site by controlling the width value and the ratios of the currents emitted from the lateral electrodes. As a result, the authors succeeded in narrowing the stimulation region by controlling the sum of the currents emitted from the two lateral electrodes. Also they succeeded in continuously moving the stimulation site by modifying the currents emitted from the two lateral electrodes.

Chromosomal localization of a gene responsible for vestibulocochlear defects of BUS/Idr mice: identification as an allele of waltzer.

Mice of the bustling mutant strain BUS/Idr have vestibulocochlear defects. bus/bus homozygotes, but not heterozygotes, are hyperactive and display an abnormal behavior such as circling, head bobbing and head tilting. To characterize BUS mice further, the auditory brain-stem response of the mutant was examined. In +/bus heterozygotes as well as control animals, the auditory brain-stem response was developmentally first recorded as early as 11 days of age and heterozygous and normal adults showed typical auditory brain-stem responses with five peaks in a threshold of 40-45 dB SPL. In contrast, bus/bus homozygotes showed no auditory brain-stem response at any age in response to stimuli up to 130 dB SPL, indicating that they are deaf throughout life. Linkage analysis revealed that the responsible gene, originally designated as bus, maps on chromosome 10, 1.09+/-0.9 cM distal to D10Mit127 and D10Mit59, and 0.72+/-0.51 cM proximal to three markers, D10Mit48, D10Mit112 and D10Mit258, at a site indistinguishable from that of the Albany waltzer, v(A/b). The results of allelism tests between BUS and Albany waltzer indicated that bus is allelic with v(Alb). From these data, we propose here that the bus mutation could represent another allele of waltzer, now designated v(bus).

Glycolipids in Rat Cochlea

In recent years, the functions of glycolipids have been intensively studied. Before the research of the roles of glycolipids in the inner ear, it seemed to be necessary to demonstrate the composition of glycolipids at first. Therefore, rat cochlea has been examined for glycolipid composition in the present study. Glycolipids extracted from 200 cochlea samples were separated into neutral and acidic glycolipid fractions. Each fraction was analyzed by thin-layer chromatography. The neutral glycolipid was almost exclusively galactosylceramide (cerebroside) with trace amounts of globoside and unidentified glycolipids. In acidic glycolipids, sulfated galactosylceramide (cerebroside sulfate) was most abundant. Of the gangliosides (sialic acid-containing glycolipids), ganglioside GM3 (51.8%) was the predominant component, and GM2 (6.0%), GM1 (8.8%), GD3 (10.7%), GD1a (8.7%), GD1b (5.9%), and GT1b (3.6%) were also detected. In addition to these, rat cochlea also contained several, minor, unidentified gangliosides. This pattern of the cochlear acidic glycolipids is very similar to that of the renal acidic glycolipids. This finding seems to be very interesting when considering that the toxic side effects of aminoglycosides occur only in the kidney and the inner ear.

A new model of auditory prosthesis using a digital signal processor

Abstract A new model of an extracochlear prosthesis has been developed using a digital signal processor. As a speech coding method, a new idea has been proposed to simulataneously transmit the pitch signal and the second formant frequency through an electrode. A digital signal processor was used to extract both pitch and second formant frequencies in real time. This new method of speech coding has proven effective for discrimination of the five Japanese vowels.

Design of an implantable tinnitus suppressor by electrical cochlear stimulation

The elecmcal cochlear stimulation was applied 123 times in total to tinnitus treatment using a tinnitus suppressing system with magnetic coupling coils. From the subjective responses, it was found that the treatment was effective for 63.3 % of the patients. The treatment effeicacy was more than 60 % when the stimulation frequency was one of 200, 600, and loo0 Hz although it decreased to 40 % at 2000 Hz. The efficacy was about 80 % for the patients who have suffered from tinnitus for less than one year. Our system was implanted in this year so that the tinnitus can be suppressed whenever it appears. INTRODUCTION It has been known that fifty or sixty percent of hearing impaired patients suffer from tinnitus which causes them , stress and sleeplessness. In 1976. House reported that electrical stimulation lo the cochlea suppresses tinnitus to some extent1). This effect was also observed in the course of developing our single channel extracochlear prosthesis. We have treated tinnitus patients using a tinnitus suppressor which we had developed. With this treatment about sixty percent of the patients answered that the tinnitus was suppressed and any side effects were not observed. This method, however, suppresses tinnitus for only a short period of time, so many tinnims sufferers have long been waiting for an implant system which can suppress tinnitus whenever it appears. The effect of tinnitus suppression by the electrical cochlear stimulation was evaluated for 128 patients and an implantable tinnitus suppressor was developed using a technology of a single channel exuacochIear prosthesis. METHOD The tinnitus suppressor consists of a wave generator, a primary coil inside the ear, a secondary chip coil implanted under the skin of an extemal ear and a Pt-Ir electrode placed on the promontory of the cochlea as shown in Figure 1. Before implantation of the tinnitus suppressor, a signal transmitter consisting of the primary and the secondary coils was set up outside of the body in order to check whether the transmitter works well. The sinsoidal wave generated by a computer was sent to the primary coil through a D/A converter. The current induced in the secondary coi1 was transmitted to the Pt-Ir electrode. The induced current was monitored by a current probe and recorded on the computer memory. Figure 1. Schematic representation of an implantable tinnitus suppressor After local anesthesia, the Pt-Ir electrode was inserted through an incision hole of the eardrum and placed on the apex of the cochlea. An Ag/AgCl retum electrode was fixed to the ear lobe of the patient. The sinsoidal waves with 200, 600, lo00 and 2000 Hz frequencies were used for the stimuli although it was reported that the higher frequency than 200 Hz decreased the efficacy of treatment2). The stimulus current was gradually increased from 0 pA. After that, the current increase was stopped when either the patient complained about it or the current reached 150 pA(0 to peak). The maximum stimulus time was 2 minutes. Each patient was treated using only one of stimuli with 200,600, loo0 and 2000 Hz frequency. According to the patients subjective report, the effect was classified into five categories: Tinnitus (1) completely disappeared, (2) was significantly reduced, (3) slightly reduced, (4) not reduced at all. The first three categories (1). (2) and (3) were considered to indicate some degree of effectiveness. On the other hand, the remaining category was considered to indicate no degree of effectiveness. 92 sensorineural impaired patients underwent this tinnitus suppressing treatment. The total number of patients receiving the treatment was 128.58 of the patients were male, and 34 were female. There were 47 bilateral patients and 45 unilateral ones. 0-7803-1377-1/93

Thyroplasty Type I with Ceramic Shim

3.00 01993 TEEE 1349 RESULTS and DISCUSSION The stimulation frequency was 200 Hz in 19 cases, 600 & in 52 cases, 1000 ~z in 42 cases and 2000 & in 15 cases. Figure 2 shows the degree that tinnitus was effected: stimulation frequency was more than 200 Hz, no effect was observed2). OUr results show that the effectiveness WaS not lower even when the stimulation frequency was more than 200 Hz. The effectiveness, however. was lower when the stimulation frequency was 2000 Hz. This treatment was effective for 80 % of the patients who have suffered from tinnitus for less than one year, and for only 60 % of the patients who have suffered for more than one year. It is considered that electrical stimulation is more effective in the early stage in suppressing tinnitus. There are no meaningful effects caused by the variable of age, sex, and the threshold of the current. CONCLUSION It was found that the electrical cochlear stimulation was effective for 63.3 % of the tinnitus patients. The treatment efficacy was more than 60 % at the stimulation frequencies of 200,600, and lo00 Hz although it was 40 % at 2000 Hz. The efficacy was about 80 % for the patients who have suffered from tinnitus for less than one year.

Evaluation of the Tripolar Electrode Stimulation Method by Numerical Analysis and Animal Experiments for Cochlear Implants

To prevent side effects from a silicone shim in Isshiki thyroplasty type I, we used a ceramic shim in 10 patients with unilateral recurrent laryngeal nerve paralysis. No published reports have described the use of ceramic in this type of surgery. According to the degree of glottic insufficiency, ceramic shims of various heights were inserted into the fenestration made in the thyroid ala. All patients experienced subjective improvement of voice postoperatively. Laryngoscopies in most cases showed that glottic insufficiency improved postoperatively. In the postoperative examination, the maximum phonation time improved an average of 3.7 s, and the mean flow rate improved an average of 331 ml/s. We have analyzed the relationship of these improvements to the degree of glottic insufficiency and have compared our results with those of other investigators.

Rapidly Progressive Sensorineural Hearing Loss (Rapid Deafness)

We have proposed the Tripolar Electrode Stimulation Method (TESM) which may enable us to narrow the stimulation region and to move continuously the stimulation site for the cochlear implants. We evaluated whether or not TESM works according to a theory based on numerical analysis using the auditory nerve fiber model. In this simulation, the sum of the excited model fibers were compared with the compound actions potentials obtained from animal experiments. As a result, this experiment showed that TESM could narrow a stimulation region by controlling the sum of the currents emitted from the electrodes on both sides, and continuously move a stimulation site by changing the ratio of the currents emitted from the electrodes on both sides.