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Cochlear implants are considered the gold standard therapy for subjects with severe hearing loss and deafness. Cochlear implants bypass the damaged hair cells and directly stimulate spiral ganglion neurons (SGNs) of the auditory nerve. Hence, the presence of functional SGNs is crucial for speech perception in electric hearing with a cochlear implant. In deaf individuals, SGNs progressively degenerate due to the lack of neurotrophic support, normally provided by sensory cells of the inner ear. Adipose-derived stromal cells (ASCs) are known to produce neurotrophic factors. In a guinea pig model of sensory hearing loss and cochlear implantation, ASCs were autologously transplanted into the scala tympani prior to insertion of a cochlear implant on one side. Electrically evoked auditory brain stem responses (eABR) were recorded 8 weeks after cochlear implantation. At conclusion of the experiment, the cochleae were histologically evaluated. Compared to untreated control animals, transplantation of ASCs resulted in an increased number of SGNs and their peripheral neurites. In ASCtransplanted animals, mean eABR thresholds were lower and suprathreshold amplitudes larger, suggesting a larger population of intact auditory nerve fibers. Moreover, when compared to controls, amplitude-level functions of eABRs in ASC transplanted animals demonstrated steeper slopes in response to increasing interphase gaps (IPGs), indicative of better functionality of the auditory nerve. In summary, results suggest that transplantation of autologous ASCs into the deaf inner ear may have protective effects on the survival of SGNs and their peripheral processes and may thus contribute to longterm benefits in speech discrimination performance in cochlear implant subjects. NeuroReport 32: 776-782

Background Electrically evoked auditory brainstem response (E-ABR) is an evoked potential recorded from the auditory nerve in response to electric stimulation. It is considered a short latency evoked potential. It plays a vital role, especially after the increased number of cochlear implant receivers. Body of abstract E-ABR is characterized by three positive peaks (eII, eIII, and eV) generated from the auditory nerve, cochlear nucleus, and perhaps from neurons in the lateral lemniscus or inferior colliculus. The largest is corresponding to wave V of the acoustic one. There are differences between both acoustic auditory brainstem response (A-ABR) and E-ABR. E-ABR is characterized by larger amplitudes and shorter latencies than the acoustic, and it has a steeper latency-intensity function. There are many variables affecting the E-ABR waveform, including recording-related variables, stimulus-related variables, and subject-related variables. E-ABR has potential clinical applications in cochlear implants (pre, inter, and postoperative). Conclusion After the increase in the number of cochlear implant receivers, E-ABR provides a promising new tool that can be used to evaluate auditory nerve functions. A lot of factors affect its waveform, including recording-related factors and stimulus-related and subject-related variables. E-ABR has many clinical applications, not only in post-implantation situations but also in preimplantation.

Background This research aimed at assessing the white matter microstructural (WM) brain changes in tinnitus patients with bilateral normal peripheral hearing using diffuse tensor imaging to test whether, tinnitus alone without hearing loss can cause WM brain changes or not. Patients and materials Twenty-eight patients were enrolled in this research, 14 patients with bilateral tinnitus without hearing loss (audiometrically proven) and 14 normal hearing controls. All subjects underwent a full basic audiological evaluation, tinnitus matching, and were asked to fill the Tinnitus Handicap Inventory (THI) questionnaire. They underwent diffusion tensor brain imaging, mean diffusivity (MD) and fractional anisotropy (FA) values were measured at special parts of central auditory pathway, and parts of limbic system. A comparison between study and control groups was held as regards MD and FA at different brain sites using an independent sample Student t-test or Mann–Whitney U test. Furthermore, the relationship between THI scores and the MD/FA measures was examined by correlation tests. Results As regards FA values, some regions as [lateral lemniscus (LL), inferior colliculus (IC), frontal arcuate fasciculi (AF) and parahippocampus] showed statistically significant decreased FA values in the tinnitus group compared to Normal Hearing (NH) group (p < 0.05). As regards MD values, tinnitus patients showed significantly higher MD values at (auditory cortex, amygdala, and AF) compared to control group (p < 0.05). As regards correlations, THI scores showed statistically significant positive correlation with MD values measured at Rt Amygdala (r = 0.55, p = 0.04). Conclusions The central auditory pathway affection is proved in tinnitus patients with normal hearing (as least as evidenced by conventional audiological examinations) and the auditory-limbic association is proved so far. The involvement of IC confirms the subcortical auditory centres involvement in the generation of the tinnitus. Auditory associations are also significantly impacted by the effect of tinnitus.