Abstract:

Although binaural processing is known to be critical for sound source localization in terrestrial vertebrates, binaural processing for sound source localization in fishes has not been demonstrated. Previous physiological and neuroanatomical studies have indicated that interaural convergence is present in auditory pathway of oyster toadfish (Opsanus tau). In this study, we introduce a reversible method, otolith tipping, to evaluate the presence of binaural inputs. The normal directional response pattern (DRP) was recorded extracellularly for auditory cells in the first‐order descending octaval nucleus (DON) or the midbrain torus semicircularis (TS) using directional stimuli in the horizontal and midsagittal planes. The DRP was re‐evaluated while gently tipping the ipsilateral or contralateral otolith of the saccule to alter the normal relationship with the auditory epithelium. The DRP was also evaluated post‐tipping to ensure no damage had occurred. In the DON, ipsilateral or contralateral tipping most often altered or eliminated spike activity; in the TS, tipping most often caused a change in the shape or orientation of the DRP. The data indicate complex interactions of excitatory and inhibitory inputs, which appear to be associated with the convergence of binaural inputs in the DON and TS. [Work supported by the NIH.]