|
|
Evolution of brain complexity and processing capacity in birds: Cracking the problem using isotropic fractionator technique
Kocourek, Martin ; Němec, Pavel (advisor) ; Sedláček, František (referee) ; Kratochvíl, Lukáš (referee)
The most fundamental principle of comparative sciences has always been and still is the search for similarities and differences. Maybe that is why people are fascinated by the cognitive abilities of birds like corvids and parrots and their similarities to those of humans. For a long time, the prevailing explanation for the unique abilities of these species was their high relative brain size. However, the brain's processing capacity is not based on its size but on its internal architecture and the number of neurons and synapses. Today, we already have data on the numbers of neurons for hundreds of mammalian, avian, and reptilian species, obtained with the isotropic fractionator. In this thesis, I analyse cellular scaling rules for brains of birds and compare them between avian clades. Bird brains are characterized by large numbers of neurons and high neuron densities, which are comparable to those of mammals in gallinaceous birds (Galliformes) and in passerine birds (Passeriformes) and parrots (Psittaciformes) even exceed those observed in primates. The distribution of neurons is also different. In songbirds and parrots, the majority of neurons are typically located in the telencephalon, specifically in the pallium. The latest data suggest that this is a common feature of core land birds...
|
|
| |
|
|
Cellular scaling roles for passerine brains
Kocourek, Martin ; Němec, Pavel (advisor) ; Kratochvíl, Lukáš (referee)
Many passerine birds, particularly corvids, are known to express complex cognitive skills comparable to those observed in primates. In order to examine how these similarities are reflected at the cellular level, I counted neurons and nonneuronal cells in passerine brains using the isotropic fractionator method. I show that, in these birds, neuronal numbers scale almost isometrically with telencephalic size, i.e., the average neuron size shows little increase and neuronal density decreases minimally as brains get larger. Neuronal densities in the passerine telencephalon exceed those observed in the primate cerebral cortex by a factor of 3-6. As a result, the number of telencephalic neurons in the Common Raven (Corvus corax) equals those observed in the cerebral cortex of small monkeys. The cerebellum features similar scaling rules. However, because the relative size of the cerebellum is smaller than in mammalian brains, cerebellar neurons make a much smaller proportion of total brain neurons than in mammals. In contrast to the little variation in neuronal densities in telencephalon and cerebellum, the density of neurons rapidly decreases with increasing structure size in the diencephalon, optic tectum and brain stem. For all examined brain structures, the densities of nonneuronal cells remain constant...
|
|
| |
guest ::
RSS feed.