Criticality and Active Dynamics in Mechanical Detection by the Inner Ear

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

The auditory (hearing) and vestibular (balance) systems provide us with rich information about the world around us. To achieve this, these sensory systems perform remarkable mechanical detection, responding to very small movements in the hair cells of the inner ear. This sensitivity has to be achieved even in a noisy environment in order to allow individuals to distinguish sounds that they want to hear and interpret from background noise. While the fundamental process of hearing is known, the processes that support acuity of hearing (being able to clearly detect the important sounds) are not well understood. This project will look at the fundamental mechanics and physics of the response of hair cells in order to better understand the dynamics of the hearing process. Beyond advancing understanding of this important physiological process, the knowledge gained from the research may also inform the development of sensor systems that mimic the process of the ear. The award will enable the inclusion of undergraduate researchers, recruited through programs that broaden the participation of students from under-represented minorities. The laboratory will also include high school students in the research project, focusing on encouraging women to pursue studies in this field. This project has two guiding hypotheses. First, that the coupling between hair cells changes the dynamics of the system, poising it closer to criticality. Second, that the presence of weak chaos in the coupled system enhances its sensitivity. In order to investigate thse hypotheses, this project will use in vitro preparations of the bullfrog sacculus to assess how coupled systems of hair bundles achieve their detection. Specifically, the research will look for signatures of criticality, which would be a regime that leads to a highly sensitive response and a broad range of power-law behavior. The project will also explore the role of chaotic dynamics in the fully coupled system in order to determine how chaoticity in individual bundles is modified by the coupling, as well as how it affects the performance of the full system. To elucidate the role of these dynamic regimes, the project will use preparations that incorporate different coupling conditions. For one set of experiments, it will use hybrid preparations, in which different numbers of hair bundles will be connected to build arrays of different sizes. For another set of experiments, semi-intact systems will be used, which preserve the innate, overlying membrane. The researcher hypothesizes that the system is poised near criticality, on the weakly oscillatory side, and that the critical oscillations exhibit chaotic dynamics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.