Representations of taste in the zebrafish brainstem

How does our brain work? Understanding how the sensory information is being processed in the ¨brain and generates behaviors is one of the great est challenges of science in our century. Ac tivity of single neurons have been investigated in ¨great detail. However, neurons do not work in iso lation. They are organized in circuits that proces s key information to perform higher brain fun ctions. In order to understand these brain ci rcuits the use of functional imaging has been ¨established as an excellent tool for monitoring n etwork activity with high spatial and tempora l resolution. Therefore, during the first par t of my thesis, I developed a framework of al gorithms to extract relevant information from func tional imaging in order to understand the activity ¨of thousands of neurons. The second a im 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-def ined and simple sensory system which coding strate gies are still a matter of debate. In order¨ to study the neural mechanisms inherent to gustato ry information processing, I focused on the brains tem, the first relay of taste processing in the ce ntral nervous system. Brainstem circuits are a ver y attractive system for studying the basic computa tions underlying simple reflex motor outputs. More over, in the particular organization of the zebraf ish, this circuits are rather accessible. My ¨results showed that taste categories (sweet, sour , bitter, salt and umami) are represented by dissi milar brainstem responses and generate different b ehaviors. I also showed that the intensity percept ion of different categories is encoded by differen t principles. On the other hand, the food we ¨consume is a combination of different tastants fr om different categories. Then, how does the b rainstem cope with such mixtures? I observed that¨ taste mixtures generates nonlinearities in th e activity of the brainstem circuits that may suggest the presence of complex coding mechanisms such as dynamic gain modulation and neural a ttractors. These mechanisms might be used for a be tter food detection or more efficient rejecti on of inedible substances. For the first tim e, to the best of my knowledge, it has been s hown that these kind of higher level computat ions can occur in this primitive but evolutionary¨ conserved taste processing center in the brainstem .nrpages: 126status: publishe