Acoustic to Electric Pitch Comparisons in Cochlear Implant Subjects with Residual Hearing

The aim of this study was to assess the frequency-position function resulting from electric stimulation of electrodes in cochlear implant subjects with significant residual hearing in their nonimplanted ear. Six cochlear implant users compared the pitch of the auditory sensation produced by stimulation of an intracochlear electrode to the pitch of acoustic pure tones presented to their contralateral nonimplanted ear. Subjects were implanted with different Clarion® electrode arrays, designed to lie close to the inner wall of the cochlea. High-resolution radiographs were used to determine the electrode positions in the cochlea. Four out of six subjects presented electrode insertions deeper than 450°. We used a two-interval (one acoustic, one electric), two-alternative forced choice protocol (2I-2AFC), asking the subject to indicate which stimulus sounded the highest in pitch. Pure tones were used as acoustic stimuli. Electric stimuli consisted of trains of biphasic pulses presented at relatively high rates [higher than 700 pulses per second (pps)]. First, all electric stimuli were balanced in loudness across electrodes. Second, acoustic pure tones, chosen to approximate roughly the pitch sensation produced by each electrode, were balanced in loudness to electric stimuli. When electrode insertion lengths were used to describe electrode positions, the pitch sensations produced by electric stimulation were found to be more than two octaves lower than predicted by Greenwood's frequency-position function. When insertion angles were used to describe electrode positions, the pitch sensations were found about one octave lower than the frequency-position function of a normal ear. The difference found between both descriptions is because of the fact that these electrode arrays were designed to lie close to the modiolus. As a consequence, the site of excitation produced at the level of the organ of Corti corresponds to a longer length than the electrode insertion length, which is used in Greenwood's function. Although exact measurements of the round window position as well as the length of the cochlea could explain the remaining one octave difference found when insertion angles were used, physiological phenomena (e.g., stimulation of the spiral ganglion cells) could also create this difference. From these data, analysis filters could be determined in sound coding strategies to match the pitch percepts elicited by electrode stimulation. This step might be of main importance for music perception and for the fitting of bilateral cochlear implant

Frey syndrome treatment with botulinum toxin

The goal of this work is to present our results of the intradermic infiltration with botulinum toxin in patients with Frey syndrome. Sixteen hemifaces in 15 patients were studied. Gustatory stimulation was evoked by sucking on a slice of lemon while measurements were done on both hemifaces, with the normal side being used as a control. Skin temperature and color (erythema) were measured with a digital surface thermometer and a skin chromameter, respectively. Sweat quantity and surface were measured by using the previously described blotting paper and iodine-sublimated paper histogram methods, respectively. Testing was repeated 2 weeks after skin infiltration with botulinum toxin (dilution of 50 U/mL). The interinjection distances were 1 cm, and 0.1 mL (5 U) was infiltrated at each injection site. Frey syndrome complaints disappeared in all patients. Small residual amounts of sweat were measurable. The difference in sweat quantity before and after botulinum toxin infiltration was significant in every patient (P < 0.001). Skin temperature and color measurement gave inconclusive results. In conclusion, Frey syndrome treatment with botulinum toxin is an efficient and well-tolerated technique. Further work should address the optimal injection parameters

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

Functional MRI of auditory cortex activated by multisite electrical stimulation of the cochlea

Electrical stimulation of the ear of deaf patients via cochlear implants offers a unique occasion to study activity of central auditory pathways with fMRI, without bias due to scanner noise. Such measurements, however, require one to control the possible interference between fMRI acquisition and the implanted electrodes. A series of measurements on a customized phantom designed to characterize the level of induced currents during MRI acquisition is presented. These experiments demonstrate that the major artifactual contribution is due to radiofrequency interaction and that safe experimental conditions can be obtained with proper shielding of the stimulation cables. The induced currents could be reduced to low levels (<50 microA for a duration <2 ms), below the acoustic perceptual threshold of cochlear implant subjects. Subsequent fMRI experiments on a patient using an Ineraid cochlear implant were conducted. Results revealed bilateral localized activation of the primary auditory cortex. Stimulation of two different intracochlear electrodes elicited activity in two neighboring, but different, regions, in agreement with the known tonotopical organization of the auditory cortex. This work paves the way for fMRI studies of a broad selection of auditory paradigms without interference from unwanted noise

Prevention of Frey syndrome during parotidectomy

To evaluate the incidence of Frey syndrome (auriculotemporal nerve syndrome) after parotidectomy with and without placement of a subcutaneous implant and to examine the relationship between different implants and postoperative wound complications (hematoma, seroma, salivary fistula)

New objective and quantitative tests for gustatory sweating

Two newly developed tests for gustatory sweating, providing both quantitative and topographic information, are presented. In both tests a paper stencil shaped to fit the complex anatomy of the parotid region is used. The blotting paper technique uses the difference in weight before and after gustatory stimulation to measure the amount of sweating. The iodine-sublimated paper histogram (ISPH) uses iodine sublimated office paper that changes colour when wet. The paper stencil is than digitized and a histogram algorithm applied to measure the area of sweating. A calibration of these tests with known and appropriate quantities of saline is presented

Perception du langage des utilisateurs d'implants cochléaires récents

Une grande partie des implants cochléaires de dernière génération utilisent des stratégies du codage des sons, dites CIS, dont les particularités essentielles sont de stimuler toujours les mêmes électrodes implantées, les unes après les autres, à une vitesse très rapide. Nous décrivons ici la perception du langage de deux groupes d'adultes utilisant ce type de codage des sons sur deux systèmes d'implants cochléaires très différents : un système développé il y a presque vingt ans mais bénéficiant d'un nouveau processeur de recherche et un système commercial très récent. Cette étude montre que tous ces patients obtiennent grâce au codage CIS une bonne perception du langage, permettant à la majorité d'entre eux de converser au téléphone