title: Olfaction, navigation, and the origin of isocortex.
abstract: There are remarkable similarities between the brains of mammals and birds in terms of microcircuit architecture, despite obvious differences in gross morphology and development. While in reptiles and birds the most expanding component (the dorsal ventricular ridge) displays an overall nuclear shape and derives from the lateral and ventral pallium, in mammals a dorsal pallial, six-layered isocortex shows the most remarkable elaboration. Regardless of discussions about possible homologies between mammalian and avian brains, a main question remains in explaining the emergence of the mammalian isocortex, because it represents a unique phenotype across amniotes. In this article, we propose that the origin of the isocortex was driven by behavioral adaptations involving olfactory driven goal-directed and navigating behaviors. These adaptations were linked with increasing sensory development, which provided selective pressure for the expansion of the dorsal pallium. The latter appeared as an interface in olfactory-hippocampal networks, contributing somatosensory information for navigating behavior. Sensory input from other modalities like vision and audition were subsequently recruited into this expanding region, contributing to multimodal associative networks.
authors.affiliation: Departamento de Psiquiatría, Escuela de Medicina, Centro Interdisciplinario de Neurociencia, Pontificia Universidad Católica de Chile Santiago, Chile.
authors.forename: Francisco
authors.initials: F
authors.lastname: Aboitiz
authors.affiliation: Facultad de Medicina, Centro de Investigación Biomédica, Universidad Diego Portales Santiago, Chile ; MRC Functional Genomics Unit, Department of Physiology, Anatomy and Genetics, University of Oxford Oxford, UK.
authors.forename: Juan F
authors.initials: JF
authors.lastname: Montiel
keywords: hippocampus; isocortical evolution; olfaction; plasticity