BME PhD Defense: Adam Dziorny

Exposure to an Augmented Acoustic Environment (AAE) Improves Neural Correlates of Auditory Processing

Supervised by Prof. Anne Luebke and Prof. Joseph Walton

Abstract

Each year as many as 3/1000 children are diagnosed with congenital sensorineural hearing loss. Common in these children are delays in grammar comprehension, vocabulary retention and speech development. Many children also show deficits in fundamental sound perception such as temporal processing. Previous studies in a mouse model (DBA/2) of congenital sensorineural hearing loss suggest that early exposure to an augmented acoustic environment (AAE) limits outer hair cell death and maintains peripheral auditory thresholds. We hypothesized that a temporally complex AAE would also have beneficial effects on neural correlates of temporal processing in the central auditory system. We assessed peripheral auditory function using ABR and DPOAE measures, and investigated central auditory function using multiunit recordings from the inferior colliculus of the DBA/2 mouse.

In Aim I, we presented a temporally-complex AAE containing silent gaps embedded in noise bursts to mice from birth to P30. Exposure to the AAE resulted in preserved peripheral function, and auditory midbrain neurons showed significant improvement in excitatory receptive fields. A gap-in-noise paradigm was used to assess neural correlates of temporal acuity. We found that units from AAE exposed mice displayed shorter neural gap thresholds when compared to controls. In Aim II, we asked whether delaying the exposure onset or altering its duration modified the improvements in neural processing observed in Aim I. We found that the time of onset of the AAE exposure is of little importance in improving auditory function, however continued exposure is essential to maintain the beneficial effects and limit the functional loss.

Overall, our results demonstrate that exposure to AAE preserves peripheral structure and function, and improves central auditory processing. Moreover, the type and duration of AAE exposure is critical in delaying the progression of sensorineural hearing loss. These experiments pave the way for possible therapeutic AAE intervention in infants diagnosed with congenital sensorineural hearing loss.