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.

人们认为灵长类动物拥有动物王国中最先进的认知技能。然而，像一些鸦和鹦鹉这样的鸟类物种表现出的认知能力似乎与非人类灵长类动物的技能相当。这反映在他们使用工具、进行因果推理、展示未来计划和想象力的能力上。尽管这些鸟类和非人类灵长类动物的认知能力非常相似，但它们的大脑组织却大不相同。因此，假设高级认知能力可以基于不同的神经元结构是可行的。然而，这就提出了一个问题：哪些因素促成了灵长类动物和某些鸟类的这种特殊大脑的进化，只有这些物种表现出先进的认知技能。大脑的绝对大小和相对大小似乎不足以解释脊椎动物之间认知能力的差异。高级认知功能的进化发展必须依赖于其他因素。最近在灵长类动物身上发现了这种可能的因素。灵长类动物的大脑与其他哺乳动物大脑的不同之处在于它们的神经元缩放规则，这使得它们每脑容量比其他哺乳动物积累更多的神经元。初步数据表明，包括鸦科在内的雀形目鸟类与灵长类动物共享这种缩放规则。因此，类似的神经元尺度规则可能是灵长类动物和鸦类动物高级认知技能之间的联系因素。本项目旨在量化鸟类不同前脑区域的神经元数量，以研究这种有利的缩放规则是否存在于具有高级认知技能的鸟类物种中，以及这些缩放规则是否特定于某些大脑区域。因此，我计划分析与鸟类高级认知功能有关的大脑区域的细胞组成，例如与主要运动和感觉区域相比的Nidopallium/Mesopallium。细胞组成将通过使用一种最新开发的方法：各向同性分馏技术进行研究。这种方法可以精确测量给定区域内的神经元数量，而不受细胞分布不均一性的影响。该分析将在四种鸦科动物和三种鹦鹉以及其他五种没有表现出非凡认知能力的鸟类中进行。我预计，与其他鸟类相比，与高级认知能力相关的大脑结构在鸦和鹦鹉中会显示出更高的细胞密度。另一方面，与认知不太相关的区域的细胞密度预计与给定物种的运动/感觉特征成比例。如果是这样的话，这项研究将首次深入了解两个不同组织的神经元系统中高级认知能力发展的神经元先决条件。

It is believed that primate species possess the most advanced cognitive skills in the animal kingdom. However, avian species like some corvid and parrot species show cognitive abilities which seem to match the skills of non-human primates. This is reflected in their capability to use tools, perform causal reasoning and exhibit future planning as well as imagination. Although the cognitive abilities are highly similar between these avian species and non-human primates, their brain organization is vastly different. Therefore, it is feasible to assume that advanced cognitive abilities can be based on different neuronal architectures. This, however, raises the question of which factors have contributed towards the evolution of such specialized brains in both primates and certain avians, that only these species evince advanced cognitive skills. Absolute and relative brain size seem to be insufficient to explain the differences in cognitive skills within vertebrates. Evolutionary development of advanced cognitive functions has to depend on other factors. Such a possible factor has recently been identified in primates. Primate brains differ from other mammalian brains in their neuronal scaling rules allowing them to accumulate more neurons per brain volume than other mammalian species can. Preliminary data indicates that Passeriformes birds, which include corvids, share this scaling rule with primates. Therefore, comparable neuronal scaling rules could be the connecting factor between the advanced cognitive skills in primate and corvids. The aim of the presented project is to quantify the number of neurons in different forebrain areas of birds to investigate if such favorable scaling rules are present in avian species with advanced cognitive skills, and if these scaling rules are specific to certain brain areas. For this reason I plan to analyze cellular composition of brain areas which have been shown to be related to advanced cognitive functions in birds, such as the Nidopallium/Mesopallium in comparison to primarily motor and sensory areas. Cellular compositions will be investigated by using a recently developed method: the Isotropic fractionator technique. This method allows precise measurements of neuron numbers within a given area not affected by heterogeneity in cellular distribution. The analysis will be done in four corvid and three parrot species, as well as five other avian species which do not show extraordinary cognitive skills. I expect that brain structures associated with advanced cognitive abilities will show higher cell densities in corvid and parrot species in contrast to other birds. On the other hand, cellular densities of areas less related to cognition are expected to scale with motor/sensory characteristics of the given species. If this is the case, this study will provide the first insight into the neuronal prerequisites which allow the development of advanced cognitive abilities in two differently organized neuronal systems.