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First published online May 1, 2009
Journal of Experimental Biology 212, 1483-1493 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026898

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Physiological evidence for binaural directional computations in the brainstem of the oyster toadfish, Opsanus tau (L.)

Peggy L. Edds-Walton^1,* and Richard R. Fay²

¹ Parmly Hearing Institute, Loyola University Chicago, Chicago, IL 60626, USA
² Neuroscience Institute, Marine Biological Laboratory, Woods Hole, MA 02543, USA

^* Author for correspondence (e-mail: plewalton{at}yahoo.com)

Accepted 23 February 2009

Comparisons of left and right auditory input are required for sound source localization in most terrestrial vertebrates. Previous physiological and neuroanatomical studies have indicated that binaural convergence is present in the ascending auditory system of the toadfish. In this study, we introduce a new technique, otolith tipping, to reversibly alter directional auditory input to the central nervous system of a fish. 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 particle motion stimuli in the horizontal and mid-sagittal planes. The same stimuli were used during tipping of the saccular otolith to evaluate changes in the DRPs. Post-tipping DRPs were generated and compared with the pre-tipping DRPs to ensure that the data had been collected consistently from the same unit. In the DON, ipsilateral or contralateral tipping most often eliminated spike activity, but changes in spike rate (±) and DRP shape were also documented. In the TS, tipping most often caused a change in spike rate (±) and altered the shape or best axis of the DRP. The data indicate that there are complex interactions of excitatory and inhibitory inputs in the DON and TS resulting from the convergence of binaural inputs. As in anurans, but unlike other terrestrial vertebrates, binaural processing associated with encoding the direction of a sound source begins in the first-order auditory nucleus of this teleost.

Key words: auditory, descending octaval nucleus, torus semicircularis, directional hearing

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