http://dx.doi.org/10.1098/rstb.2015.0060
by Harvey J. Karten
This review paper covers not just the history of studies on avian brain which dates back to the Darwin era, but it also tells the story of the author's long quest for the answer of how laminar structure of mammalian neocortex was developed and it had diverged from the nuclear structures of avian brain.
Mammalian brain and avian brain are very different in forebrain organization. The mammalian brain has laminated cortex structure. In contrast, the avian brain has nuclear clusters that are interconnected. Despite such differences, both animals can perform complex cognitive behaviors, such as sensory perception, decision making, and language capability.
Recent studies have suggested homology in the molecular features of neurons and the structures of microcircuits (Wang et al., 2010). This "nucleus to layer" hypothesis was further supported by Dugus-Ford et al. (2012) showing that each of the distinct nuclei of the avian telencephalon also expressed various genetic molecular features that very closely match those of layers of the mammalian neocortex to which they were speculatively linked. Such homology can track back to fish. Calabrese and Woolley (2015) demonstrated that the avian auditory pallium exhibits the same information-processing principles that define the canonical cortical microcircuit, which is similar to the lamina-specific properties of mammalian cortex. They provided a physiological explanation for the evolution of neural processes that give rise to complex behavior in both mammals and birds.
The author has also stated several times in this paper that the microcircuit structure that is commonly seen in vertebrate brains may have originated from the age that is older than the ancestoral reptile of avian and mammals. It is fun to imagine how birds and mammals employed microcircuit as a common building block to built their own brains.
Overall, the paper was mostly written in plain English and it was fun to read.
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