Quantitative analysis of neuronal cells in specific brain areas of different avian orders: Comparison of avian species with high cognitive abilities to species with lower cognitive skills.
Evolutionary Cell and Developmental Biology (Zoology)
Human Cognitive and Systems Neuroscience
Molecular Biology and Physiology of Neurons and Glial Cells
Final Report Abstract
It is believed that primates possess the most advanced cognitive skills in the animal kingdom. However, avian species like some members of the corvid family (e.g. crows and ravens) show cognitive abilities matching the skills of non-human primates. Although cognitive abilities are highly similar between corvids and non-human primates, their brain organization is vastly different. This raises the question, which factors render the brains of primate and corvid species so special that only in these species an evolution of advanced cognitive skills could take place. Recent studies have shown that primates can accumulate more neurons per brain volume than other mammalian species. Preliminary data indicates that Passeriformes birds, which include corvids, share this ability with primates. It is possible that this ability is responsible for the higher cognitive skills in both taxa. The aim of this project was to quantify the number of cells in different forebrain areas of corvid (Carrion Crow, Hooded Crow, Rook) and noncorvid birds (Pigeon, Chicken, Ostrich). This was done, since it is likely that specific brain areas related to higher cognitive functions (Nidopallium, Mesopallium) accumulate more cells in species with advanced cognitive skills than in species with lesser cognitive abilities. Cell numbers in areas with mainly motor/sensory characteristics should, however, scale independent of cognitive abilities. Six telencephalic areas of three corvid and three non-corvid species were delineated and cell numbers were acquired using the Isotropic fractionator method. Cell numbers differed vastly in between species. This was, however, mainly driven by the weight of the given structure. With the exception of ostriches, cell densities did therefore only vary slightly between species in a given area. In general, cell densities were highest in the Striatum followed by Hyperpallium, Mesopallium, Nidopallium, Arcopallium and Hippocampus. In Ostriches cell densities were on average 3 to 6 times lower than in the other species. Although there was a trend for an increase of hyperpallial, mesopallial and nidopallial cell densities in Carrion Crows and Rooks, no major differences in cell densities between corvid and non-corvid species (excluding ostriches) within Meso- and Nidopallium could be found. Distribution of total telencephalic cells to the individual areas showed, however, interesting differences. Again, strongest differences were observed between ostriches and the remaining species. In ostriches the majority of total telencephalic cells is accumulated in the Hyperpallium, while in the other species, the Nidopallium contains the majority of cells. Yet, most important for this study were the differences between corvid and non-corvid species regarding nidopallial values. Corvids accumulate on average 5% more of their total telencephalic cells to the Nidopallium than the observed non-corvid species. This is in line with prior studies showing an increase in nidopallial volume in avian species with advanced cognitive abilities. It is therefore possible that the highly developed cognitive abilities in corvids are based on a higher allocation of cells in the Nidopallium accompanied by an increase in nidopallial volume.
