Representation of particle motion in the developing midbrain

Abstract

In underwater organisms such as tadpoles, both particle motion and pressure components provide important information about ambient sound sources. Using both anatomical and physiological techniques, we examined the representation of these components in the developing midbrain. Afferents from the lateral line and from the saccule both project to the medial vestibular nucleus in the medulla which, in turn, sends projections to the laminar nucleus of the torus semicircularis in the midbrain. Extracellular recordings from the laminar nucleus of tadpoles from early larval through metamorphic climax stages show robust responses to particle motion, but across a more constrained frequency range than observed in the medulla. Combined with earlier data showing good responses to the pressure component of sound sources, these data suggest that the laminar nucleus may be a site of integration of particle motion and pressure sensitivity.