PhD defence A. (Andrius) Plauška

The ability to localize sounds is important for many species, including humans. We need both ears to localize sounds accurately in the horizontal plane. Sound coming from -say- the left side reaches the left ear earlier than the other one. Our brain uses these tiny differences in arrival times of low-frequency sounds to compute where they are coming from. This computation is done by the medial superior olive (MSO), a nucleus in the brainstem. MSO neurons have a simple structure: they have only two main dendrites, each receiving sound information from only a single ear. These neurons preferentially fire when information arrives simultaneously at both dendrites, meaning that the difference in travel time between both ears to the neuron must somehow compensate for the difference in arrival time at both ears of the sound.

In this thesis, we investigated in Mongolian gerbils, which have good low-frequency hearing, how the MSO neurons integrate information from both ears. We found that MSO neurons sum the incoming information from both ears linearly at their cell body (1+1=2), but that their firing probability is a nonlinear function of the size of the incoming information (1+1 is >3). Furthermore, we obtained evidence that the most likely source for the difference in travel time for the information coming from both ears lies within the brainstem, whereas the inner ear and the MSO itself are much less likely candidates. The elucidation of these cellular mechanisms will hopefully aid further research into sound localization and hearing restoration.

Due to corona, the PhD defences do not take place publicly in the usual way in the Senate Hall or in the Professor Andries Querido Room. The candidates will defend their dissertation either in a small group or online.