Coding principles of the canonical cortical microcircuit in the avian brain

Significance A six-layered neocortex is a hallmark feature of the mammalian brain. Connections among layers and progressive changes in the neural coding properties of each layer define a microcircuit thought to perform the computations underlying complex behavior. Birds lack a six-layered cortex. Yet, they demonstrate complex cognition and behavior. Recent anatomical studies propose that adjacent regions of the avian pallium are homologs of neocortical layers. Here, we show that the avian auditory pallium exhibits the same information-processing principles that define the mammalian neocortical microcircuit. Results suggest that the cortical microcircuit evolved in a common ancestor of mammals and birds and provide a physiological explanation for neural processes that give rise to complex behavior in the absence of cortical lamination. Mammalian neocortex is characterized by a layered architecture and a common or “canonical” microcircuit governing information flow among layers. This microcircuit is thought to underlie the computations required for complex behavior. Despite the absence of a six-layered cortex, birds are capable of complex cognition and behavior. In addition, the avian auditory pallium is composed of adjacent information-processing regions with genetically identified neuron types and projections among regions comparable with those found in the neocortex. Here, we show that the avian auditory pallium exhibits the same information-processing principles that define the canonical cortical microcircuit, long thought to have evolved only in mammals. These results suggest that the canonical cortical microcircuit evolved in a common ancestor of mammals and birds and provide a physiological explanation for the evolution of neural processes that give rise to complex behavior in the absence of cortical lamination.