The brain processes sensory information in a succession of interconnected brain areas. Response complexity tends to increase with distance from the sensory organ, and neurons in higher brain areas exhibit complex response properties that may also reflect memory processes and behavioural associations. Little is known about how such complex representations emerge. I propose to confront this problem by studying forebrain olfactory processing in zebrafish, utilising the extensive studies available on initial processing in its olfactory bulb and its small, tractable brain size. I will focus on the zebrafish forebrain area Dp, homologous to the mammalian olfactory cortex. First, I aim to uncover principles of afferent and internal connectivity and their relation to sensory representation. Neurons impinging upon a single Dp neuron will be identified using a monosynaptically restricted transsynaptic labelling method, and will be related to the neuron’s sensory responses by 2-photon Ca2+ imaging. Optogenetics will complement this part by directly measuring how Dp neurons integrate their pre-synaptic inputs. Second, I will use behavioural manipulations to study how experience modifies sensory representation in the forebrain. To this end, I will use a simple conditioning paradigm to associate odours with either positive or negative behavioural consequences. Sensory representation in Dp will be performed after learning, to identify the effect of behavioural value on connectivity and representation. These results will provide insights into the structure, function and plasticity of neuronal circuits underlying computations in the forebrain.