Morphological Variation in the Nucleus Laminaris of Birds

Abstract

Interaural time differences (ITDs) are one of the cues used for binaural sound localisation. In birds, ITDs are computed in nucleus laminaris (NL), where a place code of azimuthal location first emerges. In chickens, NL consists of a monolayer of bitufted cells that receive segregated inputs from ipsi-and contralateral nucleus magnocellularis (NM). In barn owls, the monolayer organisation, the bitufted morphology, and the segregation of inputs have been lost, giving rise to a derived organisation that is accompanied by a reorganisation of the auditory place code. Although chickens and barn owls have been the traditional experimental models in which to study ITD coding, they represent distant evolutionary lineages with very different auditory specialisations. Here we examined the structure of NL in several bird lineages. We have found only two NL morphotypes, one of which appears to have emerged in association with high frequency hearing.