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How does our brain work? Understanding how the sensory information is being processed in the brain and generates behaviors is one of the greatest challenges of science in our century.Activity of single neurons have been investigated in great detail. However, neurons do not work in isolation. They are organized in circuits that process key information to perform higher brain functions. In order to understand these brain circuits the use of functional imaging has been established as an excellent tool for monitoring network activity with high spatial and temporal resolution. Therefore, during the first part of my thesis, I developed a framework of algorithms to extract relevant information from functional imaging in order to understand the activity of thousands of neurons. The second aim of this thesis is to study neuronal coding, how neurons process sensory information and react to external stimuli. As means to achieve that aim, I selected to study the gustatory system, a well-defined and simple sensory system which coding strate gies are still a matter of debate.In order to study the neural mechanisms inherent to gustatory information processing, I focused on the brainstem, the first relay of taste processing in the central nervous system. Brainstem circuits are a very attractive system for studying the basic computations underlying simple reflex motor outputs. Moreover, in the particular organization of the zebrafish, this circuits are rather accessible.My results showed that taste categories (sweet, sour , bitter, salt and umami) are represented by dissimilar brainstem responses and generate different behaviors. I also showed that the intensity perception of different categories is encoded by different principles.On the other hand, the food we consume is a combination of different tastants from different categories. Then, how does the brainstem cope with such mixtures? I observed that taste mixtures generates non linearities in the activity of the brainstem circuits that may suggest the presence of complex coding mechanisms such as dynamic gain modulation and neural attractors. These mechanisms might be used for a better food detection or more efficient rejection of inedible substances.For the first time, to the best of my knowledge, it has been shown that these kind of higher level computations can occur in this primitive but evolutionary conserved taste processing center in the brainstem.