Behavioral assessment of Zwicker tone percepts in rodents

The Zwicker tone illusion can serve as an interesting model for acute tinnitus, an auditory phantom percept still not fully understood. Recent mechanistic models suggest that the underlying neural mechanisms of both percepts are similar. However, to date it is not clear if animals do perceive the Zwicker tone at all, as up to now no behavioral paradigms are available to objectively assess the presence of this phantom percept. Here we introduce, for the first time, a modified version of the gap pre-pulse inhibition of the acoustic startle reflex (GPIAS) paradigm - usually used to assess the presence of a tinnitus percept in animals - to test if it is possible to induce a Zwicker tone percept in our rodent model, the Mongolian gerbil. Furthermore, we developed a new aversive conditioning shuttle box learning paradigm and compare the two approaches. We found a significant increase in the GPIAS effect when presenting a notched noise compared to flat white noise gap pre-pulse inhibition, indicating that the animals actually perceived a Zwicker tone. However, in the aversive conditioning learning paradigm, no clear effect could be observed in the discrimination performance of the tested animals. When investigating the CR+ responses, an effect of a possible Zwicker tone percept can be seen, i.e. animals show identical behavior as if a pure tone was presented, but the paradigm needs to be further improved.