WABLE J., VAN DEN ABBEELE T., GALLEGO S., et al : Mismatch negativity: a tool for the assessment of stimuli discrimination in cochlear implant subjects. Clinical Neurophysiology 2000;111:743-751 

Abstract:
Objectives: The performance of cochlear implants varies among users. This variability may be due to the ability to process auditory information. The mismatch negativity should provide an index of discrimination in cochlear implantees (Krauss N, McGee T, Carrell T, Sharma A. Neurophysiologic bases of speech discrimination. Ear Hear. 1995;16:19-37). Our aim was to analyse MMN in cochlear implant (Digisonic) subjects to assess electrode discrimination and to study the relationship between MMN and speech performance.

Methods:
The mismatch was determined by stimulating three pairs of different electrodes. Two sessions were performed with both standard and deviant stimuli reversed. Speech recognition abilities were evaluated using 4 speech tests. The statistics included the result of 6 subjects. They indicated that MMN may be obtained when stimulating two different electrodes. A difference occured between standard and deviant stimuli within a session but also when the response to the deviant stimulus was compared to the response of the same stimulus in a standard condition, validating the discrimination process. MMN latency was about 140 ms, and amplitude about -2.8 µV. No differencies were shown with respect to electrode spacing. No relationship between MMN and speech performance was found. A clinical application of this method might be to assess the auditory processing of electrical stimuli in congenitally deaf subjects at the pre-implantation stage.

CHOUARD C.H., OUAYOUN M., MEYER B., et al. : Speech Coding Strategies of the Digisonic Fully Digitized Cochlear Implant. Acta Otolaryngol (Stockh) 1994;115:264-268 

Abstract:
The Digisonic is a fully digitized cochlear implant. Because of its articulated array, its 15 electrodes can be inserted in the cochlea. Each electrode is recessed in a special silastic compartment of the array and has a very large stimulation area thanks to its large microrelief surface area. The small volume of its implanted receiver (flat cylinder diam 29 mm, 6.9 mm thick) allows it to be placed in a 2-year-old children. The 128 point FFT of this device supply the patient with a full set of sound information between 64 and 7800 Hz. Electrode stimulation mode is sequential and stimulation rhythm is programmable. Electric crosstalk is decreased by the shape of the electrode array, and optionally by special programming of the neighboring electrodes. The speech therapist may select the width and peak value of each frequency band handled by each functional electrode. Because the versatility of this digitized emitter, many speech coding strategies can be easily programmed as a function of electrode responses or particular scientific considerations. A special version of this device, consisting of a 10 separate electrodes, has been designed for use in patients with total obstruction of the cochlea. These insulated wires may be inserted one by one in the inner ear in 10 different recesses gently drilled in the bony cochlea. This device was placed in 46 patients between 1992 and 1994, including 8 young children (aged 2-9 years, mean 5 years) and 9 patients with total cochlear obstruction.

TRIGLIA J.M., BELIAEFF M., FAUGERE G. : Cochlear Implantation in a Pacemaker Patient. Laryngoscope 1996;106:1184-1186 

Abstract:
The authors present their experience with cochlear implantation in a 22 year-old patient who had a cardiac pacemaker because of a complete atrioventricular block. The question of compatibility between the cochlear implant (multichanel Digisonic DX10/E) and the pacemaker (Biotronic Nanos-01/E) was raised. After consulting the two manufacturers regarding the risk of electrical interference, the authors decided to program the pacemaker i a locked mode (VOO) and then perform cochlear implantation. When the cochlear implant was switched on for the first time, electrocardiograms were obtained to ensure that the two devices were compatible. Absolutely no interference was detected. After a 3-year follow-up, cochlear implant performance remains excellent.

VINCENT C., ZINI C., GANDOLFI A., et al. : Results of the MXM Digisonic Auditory Brainstem Implant Clinical Trials in Europe. Otol Neurotol 2002; 23:56-60 

Abstract:
Objective: To assess the potential benefit of the MXM auditory brainstem implant for patients with neurofibromatosis type 2.
Study Design: Retrospective case review.
Setting: Tertiary referral centers.
Patients: Fourteen patients with neurofibromatosis type 2 and bilateral acoustic neuromas underwent implantation with the MXM brainstem implant during surgery to remove the second-side tumor.
Results: There were no complications related to the auditory brainstem implantation. Auditory sensations were present for 12 of 14 patients (86%). Global results indicated an improved quality of life for the patients receiving auditory sensations, in part because of their auditory orientation within the environment. Eighty-nine percent of patients tested with an open-set sentence test demonstrated enhancement of speech understanding as a result of lip-reading improvement when auditory brainstem implant sound was combined with lip-reading. A few patients (36%) had some speech understanding in sound-only mode. One patient was able to have limites phone conversations.
Conclusion: These results indicate that significant auditory benefit can be derived from the MXM auditory brainstem implant.

DI NARDO W., DI GIROLAMO S., DI GIUDA D., et al. : SPET monitoring of auditory cortex by electric stimulation in patient with auditory brainstem implant. Ear Arch Otorhinolaryngol 2001;258:496-500 

Abstract:
Auditory cortex activation following multifrequency acoustic stimulation has been evaluated by means of single photon emission tomography (SPET) in one patient before and after an auditory brainstem implant (ABI). No activation could be observed after acoustic stimulation before ABI. After ABI stimulation in the coronal and axial slices, the activation within the temporal cortex controlateral to the stimulated ear was twice (43,76%) that of normal controls (23,94±2,74%). This marked difference was not present in other selected cortical auditory areas (homolateral temporal, homolateral and contralateral parietal cortices). The temporal cortex was also examined with six consecutive sagittal slices from 18.75 mm up to 56.25 mm lateral to the midline. A very strong activation (51.20%) compared with that of normal controls (9,94±7.45%) was detected in the 25.26 mm sagittal slice of the temporal cortex contralateral to the stimulated side. The remaining sagittal slices showed an almost normal post-stimulatory activation. As the 25.26 mm sagittal slice corresponds to the medial part of the auditory temporal cortex, its activation suggests that electrode stimulation is concentrated on the region of the cochlear nucleus in which the neurons that transduce high frequencies are located. SPET can be considered useful, in combinaison with electric auditory-evoked potentials, to obtain information on ABI placement and function, effectiveness of acoustic stimulation, degree of cortical stimulation and tonotopic spatial distribution of auditory cortex activation.

GALLEGO S., TRUY E., MORGON A., et al. : EABRs and Surface Potentials with a Transcutaneous Multielectrode Cochlear Implant. Acta Otolaryngol (Stockh) 1997;117 

Abstract:
In a previous study, the authors described a technique for recording ipsilateral EABRs using the DIGISONIC MXM cochlear implant (Gallego et al, Acta Otolaryngol (Stockh) 116: 228-233) and showed that the EABR input/output functions were very similar across electrodes. In the present study a test of electrode functioning based on the recording of surface potentials is presented. Then, for each electrode the relationship between EABR thresholds and hearing thresholds was determined. Lastly, the relationship between EABR parameters and patients’ performances was studied. The results show that the functioning of each implanted electrode can be assessed quickly, accurately and objectively. Furthermore it is demonstrated that a strong correlation between EABR and hearing threshold can be obtained using an automatic EABR wave detection technique. Finally, it is shown that EABR inter-peak intervals are related to patient performance. These results are of the utmost importance for cochlear implant setting in children as they indicate a method of objective assessment of the functioning of each electrode of the corresponding hearing threshold.

GALLEGO S., MICHEYL C., BERGER-VACHON C., et al. : Ipsilateral ABR with Cochlear Implant. Acta Otolaryngol (Stockh) 1996;116:228-233 

Abstract:
Ipsilateral ABR recording technique was developed with the MXM DIGISONIC DX10 cochlear implant, involving, firstly, setting of recording variables with regard to implant and ABR constraints, and, secondly, enhancement of recording quality by signal processing. The resulting recording quality then enabled us to characterize ABR latency, amplitude and wave reproductibility according to stimulus intensity and stimulation site (electrode stimulated). The findings agree with those of the literature on controlateral human and ipsilateral animal studies. Waves III and V amplitude increased with stimulus intensity. Waves III and V latency was insensitive to stimulus intensity or site. ABR quality diminished basally.

GALLEGO S., BELIAEFF M., FRACHET B., et al. : Long-term change in threshold and confort levels and dynamics in Digisonic cochlear implant bearers. 

Abstract:
Variations in thresholds level (TL), confort level (CL) and dynamics were studied in a population of 80 subjects fitted with the Digisonic cochlear implant, a French multichannel implant manufactured by the MXM company. Statistical analysis, by Anova, showed very significant changes in CL and dynamics over implantation time. This may be explained by neuronal plasticity faciliting auditory system adaptation to the electrical stimulation. Results for TL over implantation time further showed the implant system to be stable and not destructive of the auditory nervous system. This may be due to the fact that each electrode of the Digisonic implant has an in-series capacity which very accurately controls and balances the number of positive and negative charges. Such a charge balance is vital to avoid electrolysis between electrode and physiological environment.

GALLEGO S., GARNIER S., MICHEYL C., et al. : Loudness growth functions and EABR characteristics in Digisonic cochlear implantees. 

Abstract:
Electrically-evoked auditory brainstem responses (EABRs) and loudness functions were measured in 14 subjects equipped with an MXM Digisonic cochlear implant. EABRs were evoked by 75Hz pulse trains presented on the apical electrode. Loudness functions at the same rate and at a rate more conventional for psychoacoustic measurements - 300Hz - were measured using a categorical loudness-scaling procedure. The results revealed a significant difference in the loudness functions measured at 75 and 300Hz, loudness increasing more steeply with stimulus intensity for the latter rate. Significant correlations between EABR wave V thresholds and perceptual thresholds measured at both 75 and 300 Hz were observed. Furthermore, in 8 out of the 14 patients, EABR wave V satured at a stimulus level corresponding precisely to the loudest bearable, i.e., “Too loud” level for the 300 Hz stimulation rate; this same level corresponded itself to the “Comfortable” loudness level for the 75 Hz stimulation rate. On average, a nearly linear relationship was observed over the first half of the loudness range between the stimulus intensity expressed as a pulse duration in log units and wave V amplitude in dB. Although further investigation is required before maximum comfort levels can be predicted reliably from EABR measures in individual subjects, these results delineate new directions regarding the estimation of perceptual dynamic-range limits on the basis of EABR measures in cochlear implantees.

GALLEGO S., TRUY E., DURRANT J. : Electrically Auditory Brainstem Responses in cochlear implant assessment : possibility and interest. 

Abstract:
The present study is the feasibility of recording electrically auditory brainstem responses (EABR) with a temporary stimulating electrode. Preliminary study of the literature confirmed the physiological and technical feasibility of EABR with electro-stimulation of the round-window or of the promontorium. This enabled a EABR recording design to be drawn up: stimulating and recording electrode positions, recording parameters and post-recording and data processing. Finally, preliminary results for 9 cases are described. Optimising the technique enabled EABRs to be recorded in 78% of cases.