[Have we made progress in the development of a vestibular implant?]. / Queues avancées cette année dans le développement d'un implant vestibulaire?

The concept of a vestibular implant to restore balance in patients suffering from bilateral loss of function is similar to that of a cochlear implant. Motion sensors will capture head movements and this information will be transmitted to the central nervous system via electrodes implanted in the vestibular system. However, several key questions must be answered before such prosthesis could be used in humans. One is to restore a baseline neural activity in the system that can be then adequately modulated by the prosthesis, without causing unbearable symptoms. We showed that this is possible in human. This is an important prerequisite for the feasibility of a vestibular implant.

[Development of a vestibular implant for the rehabilitation of bilateral deafness]. / Développement d'un implant vestibulaire pour la réhabilitation des déficits vestibulaires bilatéraux.

The development of a vestibular implant for the rehabilitation of bilateral vestibular loss is funded on a concept comparable to that of the cochlear implant used in the rehabilitation of bilateral deafness. This paper carries an overview of the main aspects of such a development and describes the first experiments done in human subjects in Geneva.

Channel interactions with high-rate biphasic electrical stimulation in cochlear implant subjects.

Channel interactions were assessed using high-rate stimulation in cochlear implant subjects using the Ineraid electrode array. Stimulation currents were applied on one intracochlear electrode and their effects on psychophysical detection thresholds on an adjacent electrode were measured. Stimuli were trains of brief, biphasic, 50-micros/phase pulses presented at a rate of 2000 pulses per second per channel. In experiment I, we studied how the detection of a probe signal was influenced by a sub-threshold perturbation signal presented either simultaneously or non-simultaneously (with no overlap) on an adjacent electrode. Results showed that simultaneous activation led to strong channel interactions, producing threshold changes consistent with instantaneous electric field summation. Non-simultaneous activation revealed much weaker interactions, producing threshold changes of opposite sign. In experiment II, we studied how the temporal delay between perturbation and probe pulses, as well as how the level of the perturbation signal influenced non-simultaneous channel interactions. First, threshold changes when reversing the polarity of the perturbation did progressively vanish when increasing the delay between pulses. This suggested that non-overlapping stimulation of adjacent electrodes produced channel interactions that were in part due to residual polarization of the nerve membrane. Second, increasing the perturbation to supra-threshold levels produced threshold elevations that were independent of the interpulse interval. This suggested channel interactions due to neural masking. These results provide insights into the different concurrently active mechanisms of channel interactions in cochlear implant systems using this type of stimuli.

First field trials with a portable CIS processor for the Ineraid multichannel cochlear implant.

The continuous interleaved sampling (CIS) strategy is a promising sound processing strategy for multichannel cochlear implants which provides immediate improvements in speech recognition when tested on Ineraid users: patients with only a few hours of experience (in laboratory testing) with the CIS strategy score better than with the Ineraid prosthesis they used since they, were implanted. The goal of this study was to evaluate the benefits that can be gained by the use of the new strategy in every day life. Two patients, implanted with the Ineraid multichannel cochlear implant, were equipped with a portable numerical processor programmed to implement a high rate CIS strategy. Their speech recognition was evaluated periodically with consonant and vowel identification tests for more than 6 months of use. Tests were also made with the Ineraid processor during the same experimental sessions and patients were regularly interviewed about their experience. Performance with the portable CIS processor was superior or equal to that obtained previously in the laboratory with the same strategy. Both patients achieved the best scores in 6 years of cochlear implant use. Qualitative reports from the patients suggest that the CIS strategy can improve "hearing" performance of cochlear implant users in many important situations of every day life. Altogether, these results hold great promises for all users of the Ineraid multichannel cochlear implant.

A mutant of human insulin-like growth factor II (IGF II) with the processing sites of proinsulin. Expression and binding studies of processed IGF II.

A mutant of human insulin-like growth factor II (IGF II) was constructed by site-directed mutagenesis: the nucleotides coding for Ser33 and Ser39 were changed to yield Arg and Lys, respectively, thus creating two pairs of basic residues, Arg-Arg and Lys-Arg, as flanking sequences of the remaining C domain. [Arg33, Lys39]IGF II was expressed in NIH-3T3 cells as a processed two-chain peptide with a deletion of amino acid residues 37-40 and crosslinked by three disulfide bonds. This des(37-40)[Arg33]IGF II showed 3.6-fold and 7.4-fold reduced affinities to the type 1 and type 2 IGF receptor overexpressing cells, respectively, whereas the thymidine incorporation potency was the same as that of wild-type IGF II. We speculate that the discrepancy between the reduced binding to the type 1 IGF receptor and the full thymidine incorporation potency is due to the 6.1-fold reduced affinity of the expressed mutant to the co-expressed IGF binding protein 3 (IGFBP-3). The results suggest that des(37-40)[Arg33]IGF II assumes a conformation very similar to IGF II, and that the entire length of the C domain is not essential for biological activity.