Joseph A. Sisneros and Paul M. Forlano
Project Title: Collaborative Research: Mechanisms of Sound Source Localization Underlying an Ancestral Mode of Vertebrate Hearing
Proposal #: IOS-1456700 and IOS-1456743
The proposed research investigates the mechanisms used by fish to localize sound sources. The ability to locate sound sources enables animals to detect prey, avoid predators and communicate with others and is thus basic to survival in many species. While decades of behavioral, physiological and neuroanatomical research have revealed the physical cues and neural mechanisms that terrestrial animals use to localize sound, surprisingly little is known about the localization mechanisms used by fish, the oldest extant vertebrate group. Sound source localization by fishes remains an important topic in biology and the mechanisms used by fish for sound source localization remain a mystery. Collectively, the proposed experiments will elucidate the mechanisms of sound localization utilized by fish that likely formed the evolutionary foundation for more recent modes of vertebrate hearing and sound localization. As an integral part of this research program, the PIs will host 2-4 GK-12 teachers every summer and invite them to participate in field and laboratory experiments at the Friday Harbor Labs (FHL) and will develop lesson plans, student projects and an educational website with the teachers at their home institutions. The PIs will train and mentor both graduate and undergraduate students and give annual public lectures regarding the supported research at FHL.
The investigation will take an integrated behavioral, anatomical, and brain activational approach to determine whether fish are fundamentally similar to other studied vertebrates, and use binaural information (information from both ears) to localize sound, or are fundamentally different, and achieve robust localization on the basis of monaural (single-ear) information alone. The central hypothesis to be tested is that binaural integration is essential for sound source localization in midshipman. To test this hypothesis, the investigators will 1) determine which inner ear endorgans are required for sound localization behavior by testing animals in our established sound playback paradigm before and after systematic unilateral or bilateral removal of each endorgan’s otolith (saccule, lagena, utricle), 2) characterize the ipsilateral and contralateral projections of inner ear afferents from all three endorgans to known auditory processing regions in the hindbrain by bulk labeling each endorgan separately or in double or triple combination with different fluorescent-labeled dextran amine tracers, and 3) characterize the brain activation patterns resulting from controlled auditory directional stimulation in intact animals and in those that have undergone systematic endorgan removal, using c-Fos as a marker for neural activation.