Evaluation of auditory stream segregation in individuals with cochlear pathology and auditory neuropathy spectrum disorder

Background and Aim: The central auditory nervous system has the ability to perceptually group similar sounds and segregates different sounds called auditory stream segregation or auditory streaming or auditory scene analysis. Identification of a change in spectral profile when the amplitude of a component of complex tone is changed is referred to as Spectral profile analysis. It serves as an important cue in auditory stream segregation as the spectra of the sound source vary. The aim of the study was to assess auditory stream segregation in individuals with cochlear pathology (CP) and auditory neuropathy spectrum disorder. Methods: In the present study, three groups of participants were included. Experimental groups included 21 ears in each group with cochlear hearing loss or auditory neuropathy spectrum disorders (ANSD) and control group with 21 ears with normal hearing. Profile analysis was asse­ssed using "mlp" toolbox, which implements a maximum likelihood procedure in MATLAB. It was assessed at four frequencies (250 Hz, 500 Hz, 750 Hz, and 1000 Hz) for all three groups. Results: The results of the study indicate that the profile analysis threshold (at all four frequ­encies) was significantly poorer for individuals with CP or ANSD compared to the control group. Although, cochlear pathology group performed better than ANSD group. Conclusion: This could be because of poor spec­tral and temporal processing due to loss of outer hair cells at the level of the basilar membrane in cochlear pathology patients and due to the demyelination of auditory neurons in individuals with ANSD. Keywords: Auditory stream segregation; auditory scene analysis; spectral profiling; spectral profile analysis; cochlear pathology; auditory neuropathy spectrum disorders

A study on the outcome of various methods of administration of intratympanic dexamethasone in tinnitus of cochlear pathology

<p class="abstract"><strong>Background:</strong> The aim of the study was to compare the outcome of various methods of injecting intra tympanic steroids in patients with tinnitus of cochlear pathology.</p><p class="abstract"><strong>Methods:</strong> A prospective study was conducted on 56 patients with subjective tinnitus of cochlear pathology who were then divided into three groups. After thorough otological and audiological evaluation using standard questionnaire, ENT examination, pure tone audiometry, tone decay test, tinnitogram, CT scans of temporal bone and brain. Each patient underwent one of the three chosen methods of intra tympanic steroids administration randomly. The methods are 1-Tympanomeatal flap elevationand application of steroid soaked gelfoam sponge; 2-Transtympanic steroid injection; 3-Grommet insertion followed by steroid administration. These methods were performed for subjects with tinnitus of cochlear pathology from 2009 to 2011 at a neurotological clinic at Chennai. After following up on 1st, 3rd and 6 months the observations were statistically analysed. </p><p class="abstract"><strong>Results:</strong> Success rate for techniques viz tympanomeatal flap was 70%, transtympanic - 63%, grommet - 50%. But when comparing statistically all the three methods were equally successful.</p><p class="abstract"><strong>Conclusions:</strong> Intratympanic steroids for tinnitus (cochlear pathology) are a safe, simple and promising treatment option. Though all the methods of intra tympanic steroids injection had similar success rate, the tympanomeatal flap elevation method may be preferred since it can be done in a single sitting. However transtympanic injection remains the easiest and cost effective compared to the other two methods.</p>

Neural Hyperactivity of the Central Auditory System in Response to Peripheral Damage

It is increasingly appreciated that cochlear pathology is accompanied by adaptive responses in the central auditory system. The cause of cochlear pathology varies widely, and it seems that few commonalities can be drawn. In fact, despite intricate internal neuroplasticity and diverse external symptoms, several classical injury models provide a feasible path to locate responses to different peripheral cochlear lesions. In these cases, hair cell damage may lead to considerable hyperactivity in the central auditory pathways, mediated by a reduction in inhibition, which may underlie some clinical symptoms associated with hearing loss, such as tinnitus. Homeostatic plasticity, the most discussed and acknowledged mechanism in recent years, is most likely responsible for excited central activity following cochlear damage.