Auditory pathway for detection of vibration in the tokay gecko.

Otolithic endorgans such as the saccule were thought to be strictly vestibular in amniotes (reptiles, birds, and mammals), with little evidence supporting the auditory function found in fish and amphibians (frogs and salamanders). Here, we demonstrate an auditory role for the saccule in the tokay gecko (Gekko gecko). The nucleus vestibularis ovalis (VeO) in the hindbrain exclusively receives input from the saccule and projects to the auditory midbrain, the torus semicircularis, via an ascending pathway parallel to cochlear pathways. Single-unit recordings show that VeO is exquisitely sensitive to low-frequency vibrations. Moreover, VeO is present in other lepidosaurs, including snakes and Sphenodon. These findings indicate that the ancestral auditory function of the saccule is likely preserved at least in the lepidosaurian lineage of amniotes and mediates sensitive encoding of vibration. [Display omitted] [Display omitted] • The saccule in the tokay gecko inner ear projects to brainstem nucleus VeO • VeO neurons respond to low-frequency vibration • VeO projects to the higher-order auditory nuclei, including the auditory midbrain • Found in all lepidosaurs examined so far Han and Carr demonstrate a connection between the saccule and the auditory midbrain of the tokay gecko, relayed by nucleus vestibularis ovalis (VeO) in the hindbrain. In vivo recordings show VeO is sensitive to low-frequency vibrations, which are likely perceived concomitantly with sound. VeO is found in all lepidosaurs examined so far. [ABSTRACT FROM AUTHOR]