Saccular hearing; turtle model for a human prosthesis

Abstract

The saccule is a hearing organ is some vertebrates thought to be responsive to substrate vibration (bone conduction) or low-frequency aerial sound. There was likely some overlap in these functions in the course of evolution after the sensory area to become the cochlea migrated from the saccule. That overlap is preserved in extant turtles by columella (stapes) saccular coupling via fibroelastic strands; thus both organs can respond to air conduction and bone conduction stimulation. Evoked potential data, however, reflect differential AC/BC drive to the inner ear. The columellas inertia provides the force to displace the saccular wall with the tympanum providing damping. Intense AC stimulation likely stimulates the human saccule. A proprietary stapedial saccular strut is described that serves as a surgically implanted coupling device for humans, allowing more efficient use of AC saccular hearing in clinical deafness. The human saccular resonance is about 350 Hz, which should allow for sufficient speech coding for intelligibility assuming connectivity to the auditory neuraxis. BC stimulation through audible ultrasound also likely activates the saccule in individuals with profound deafness. A stand-alone stapedio-saccular strut or one used in combination with an ultrasonic hearing aid offers the potential of communication through saccular hearing.