[Auditory synaptopathy/neuropathy: clinical findings and diagnosis]. / Auditorische Synaptopathie/Neuropathie: Klinik und Diagnostik.

Auditory synaptopathy/neuropathy (AS/AN) is a special subtype of sensorineural hearing disorders with heterogeneous phenotypes and underestimated incidence. AS/AN generally develops in infancy, occasionally in adulthood. Symptoms include fluctuating, mostly bilateral hearing loss and abnormally reduced speech comprehension, especially in noisy environments. Within audiological assessments, patients with AS/AN present otoacoustic emissions (TEOAE; DPOAE) and cochlear microphonics (CM), absence of stapedius reflexes (SR) as well as absent or pathologically altered auditory evoked brainstem potentials (ABR). Children with AS/AN cannot be identified within OAE-based newborn hearing screening programs. Clinical findings, transtympanic electrocochleography (ECoG) and further diagnostic tools permit further identification of individual characteristics. In individual cases conventional amplification and the use of FM systems may improve hearing and communication skills. If these interventions, accompanied by intensive hearing, speech and language therapy are unsuccessful, cochlear implants (CI) or alternative forms of communication may be useful options for rehabilitation.

[Diagnosis and therapy of auditory synaptopathy/neuropathy]. / Diagnostik und Therapie der auditorischen Synaptopathie/Neuropathie.

Pathological auditory brainstem responses (lack of responses, elevated thresholds and perturbed waveforms) in combination with present otoacoustic emissions are typical audiometric findings in patients with a hearing impairment that particularly affects speech comprehension or complete deafness. This heterogenous group of disorders first described as "auditory neuropathy" includes dysfunction of peripheral synaptic coding of sound by inner hair cells (synaptopathy) and/or of the generation and propagation of action potentials in the auditory nerve (neuropathy). This joint statement provides prevailing background information as well as recommendations on diagnosis and treatment. The statement focuses on the handling in the german language area but also refers to current international statements.

[Examination of binaural signal processing in normally hearing subjects using electrophysiological and psychoacoustical measurements]. / Elektrophysiologische und psychoakustische Untersuchungen zur binauralen Signalverarbeitung normalhörender Erwachsener.

BACKGROUND AND OBJECTIVE: At present, only a small number of validated, clinically usable methods for the assessment of binaural hearing capabilities exist. A proposed electrophysiological measure is the registration of the brainstem-based binaural difference potentials (BDP). PATIENTS/METHODS: The BDP is calculated as the difference between the binaurally evoked registration and the sum of the two monaural registrations. Detection and stability of the BDP were examined in 24 normally hearing adults within the framework of conventional registration of auditory brainstem responses. Furthermore, the influence of interaural time differences (ITD) on the BDP was determined. In addition, lateralization of the subjects was assessed using a psychoacoustical method. RESULTS: The components of the BDP could be detected in almost all of the subjects. Moreover, they showed sufficient test-retest reliability. The impact of ITD,which causes lateralization of the stimulus,was clearly detectable for the latencies and the amplitudes of the BDP. CONCLUSIONS: Binaural difference potentials, which are easily and reliably detectable reveal a relationship to the outcome of psychoacoustical assessment of lateralization and have the potential to provide a measure for binaural hearing capacity.

[Effect of monaural deprivation on maturation of the auditory pathway in the Mongolian gerbil (Meriones unguiculatus)]. / Einfluss monauraler Deprivation auf die Reifung der Hörbahn bei der mongolischen Wüstenrennmaus (Meriones unguiculatus).

Several investigations prove that monaural acoustic deprivation induces detrimental changes in the auditory pathway. So far the major interest focused on degenerative processes on the deprived side, while effects on the contralateral untreated side were not taken into consideration. This ontogenetic study investigates effects of early monaural acoustic deprivation on the functional development of the acoustically evoked auditory brainstem response (ABR) in the Mongolian gerbil. Young gerbils were deafened by a single intracochlear application of neomycin sulfate. The ABR development on the contralateral side differed in a late developmental period from that of normally hearing animals. These changes persisted until adulthood. Between day 55 and day 90 a significant 5 dB decrease of the ABR thresholds and a significant shortening of the interpeak latency II-V occurred. The results confirm that a complete monaural deprivation during the sensible or critical period leads on the contralateral side to plastic or compensatory changes in the auditory brainstem.

A method for the induction of a cochlea-specific auditory deprivation in the gerbil (Meriones unguiculatus).

The neurophysiological effects of early electrical stimulation on the development and neural plasticity of the central auditory system in prelingually deafened children with cochlear implants are still unknown. Many of these basic questions can be answered systematically only in animal experiments. Meriones unguiculatus is a well-established animal model in hearing research. Deafening is produced by a single intracochlear application of an ototoxic aminoglycoside antibiotic (neomycin sulfate) on the 14th day after birth (DAB), i.e. before the late natural onset of hearing on the 16th DAB. A single application of the antibiotic abolishes auditory brainstem responses (ABR) to clicks completely and reduces sensitivity to low frequency tonebursts by 50 dB SPL. Scanning electron microscopy results show a destruction of the stereocilia of the inner and outer hair cells of the basal and medial cochlear turn and a reduction of those in the apical turn. Our method avoids a systemic application of antibiotics and can be used in studies dealing with the consequences of different forms of auditory deprivation, neuronal compensation processes or with ontogenetic studies and chronic electrostimulation in an animal model.