How sensory processing is occurring into the brain and how to relate behavior to neuronal activities are key questions in modern neuroscience. Understanding the neural codes underlying brain function will be of great importance for future implementation of brain-machine interfaces. This research project proposes to study the cellular and network mechanisms controlling sensory perception. In particular, we would like to precise how sensory stimuli are coded by brain networks and how these representations may be influenced by experience or modulatory brain centers. In order to address these general questions, we propose to study olfaction as model sensory system. The olfactory system is central to the behavior of rodents (animal models that we study), is highly plastic and largely modulated by the neuromodulatory brain centers. We propose to use a combination of genetic, electrophysiological, imaging and behavioral methods to study how odor information is processed in the central nervous system as it moves from the periphery to higher areas of the brain. We showed in the past that sensory information can be contained in dynamic neural ensemble. We propose to show that ensemble dynamics may be the basis of odor coding in the olfactory bulb and to describe the mechanisms underlying cortical coding that would allow us to relate neuronal activity to behavior. In addition, we hope to show the existence of a novel form of plasticity in the olfactory bulb namely ensemble plasticity. We believe that the general questions addressed in the study of these sensory systems go beyond understanding olfactory sensory perception and could potentially be generalized to the function of many brain regions.