Divergent Evolution of Brain Structures and Convergence of Cognitive Functions in Vertebrates : the Example of the Teleost Zebrafish

Abstract : The aim of my research project was to link brain structures and functions, to better understand the fundamental bases of cognition. The first part of my thesis consisted in the development of behavioral tests to analyze the essential principles of cognition. The results strongly suggest the existence of executive functions in teleosts similar to those of mammals. Then I looked for the anatomical structures responsible for these cognitive capacities, in particular in the pallium (equivalent of the mammalian cerebral cortex). However, little is known about adult zebrafish neuroanatomy. Indeed, zebrafish is often studied at larval stage. A second part of my work aimed at studying adult structures in more detail through their developmental origin. This has redefined some parts of the brain. We have discovered that some of the structures that were considered as part of the forebrain (prosencephalon) are actually part of the midbrain (mesencephalon) in zebrafish. This includes the inferior lobe, previously classified as hypothalamus. Another structure is the major sensory relay nucleus, the preglomerular nucleus, functional analogue of the thalamus (part of the forebrain) in amniotes. This sensory pathway contains the main visual pathway to the pallium. Thus, even if some structures have the same function, they may have an evolutionary and developmental origin different from structures known in mammals. In summary, similar functions have independently evolved in amniotes and teleosts. This comparative work adds new perspectives for neuroscience research. It also allows us to approach the fundamentals of cognition in a new way: what are the essential building blocks for a higher level of cognition like the human one?
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Solal Bloch. Divergent Evolution of Brain Structures and Convergence of Cognitive Functions in Vertebrates : the Example of the Teleost Zebrafish. Neurobiology. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLS073⟩. ⟨tel-02130080⟩

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