Christine Köppl and Georg Klump: Linking age-related cochlear dysfunction to the perception of temporal fine structure

Despite normal hearing thresholds, elderly people often have difficulties communicating in noisy situations. This may be due to a compromised representation of the temporal fine structure (TFS) of acoustic signals by auditory nerve fibers.
We test the behavioural auditory discrimination of stimuli that relies on TFS in Mongolian gerbils of different ages. Subsequently, the representation of such stimuli by auditory-nerve fibers and the anatomical quantification of afferent synapses in the cochleae is carried out in the same individuals.
By pharmacologically manipulating the cochlear neuropathy in young gerbils and evaluating TFS perception before and after the manipulation, we will further provide evidence for a causal link between the neuropathy and the ability to discriminate stimuli based on TFS.
This combined approach will provide for an unprecedented level of understanding of the processes linking age-related cochlear dysfunction to the perception of TFS.

 

Christine Köppl and Ulrike Sienknecht: Role of the ribbon synapse in high-frequency neural phase locking

In humans and animals with good low-frequency hearing, phase locking by the afferent fibres of the auditory nerve is known to be a salient temporal code for the central auditory system.
This project aims to explore the specific role of the hair-cell ribbon synapse in this process. The chicken is chosen as the model organism because it combines 1) robust auditory-nerve phase-locking into the kHz-range with 2) good accessibility of early embryonic stages in-ovo for established techniques of virus-mediated gene misexpression.
We use chickens with an aberrant phenotype in one ear (generated by virus-mediated gene misexpression) that specifically changes the hair cells and their innervation. We study the consequences for temporal precision of spiking, using different metrics in vivo.
Our bird work complements ongoing work on mouse hair cells by extending the concepts and available toolbox for unravelling the mechanisms for ultrafast processing at this very specialised first synapse in the auditory pathway.

Immunolabelling on a cross-section of the avian (barn owl) basilar papilla. Gray: tall hair cells (labelled by anti-HCS1), Red: presynaptic ribbons (labelled by anti-CtBP2), Cyan: neural terminals (labelled by anti-Na/K-ATPase).