Auditory Deprivation Leads to Shrinkage in Low Best Frequency Nucleus Magnocellularis Neurons

Abstract

During development in barn owls (Tyto furcata), the interaural time differences (ITDs) circuit undergoes a progressive augmentation. At the core of the ITD detection mechanism lies the nucleus magnocellularis (NM) and nucleus laminaris (NL). NM and NL neurons together orchestrate precise auditory localization. The plasticity of the brain prompted an exploration into how the experience of barn owls influence the modulation of their ITD detection circuit. Auditory researchers have long suspected the dependence of NM neurons on auditory input. Since complete auditory isolation leads to significant changes in the morphology and physiology of NM cells, an investigation into mild acoustic deprivation could show the degree of auditory dependence NM cells require to develop. A methodological approach involving the rearing of owls with unilateral ear inserts was designed to dampen the acoustic signal on one side. Upon reaching maturity, examination of the owls' brainstem revealed that NM cells situated ipsilateral to the earplug exhibited a decrease in size by approximately 7% compared to their contralateral counterparts. However, this only confined to regions corresponding to low frequency tonotopic domains. The rostral NM remained unchanged in size despite such alterations. Notably, the overall roundness or form factor of neurons within both caudal and rostral NM remained unaltered.