"Humanity has always been intrigued by the nearly mythical properties of the brain. With its billions of neurons and innumerable connections, the brain is of such complex nature, that trying to understand it may seem a vain project. Yet, by using the ‘mini-brain’ of the model organism Caenorhabditis elegans, which shares many components with the human brain but counts only 302 neurons, thorough research can penetrate into this complexity. We here pursue to deliver a much-needed understanding of how learning and memory processes are regulated by neuropeptide signaling in the brain. Neuropeptides are small regulatory proteins that are implicated in a variety of processes. Growing evidence exists for their involvement in learning and memory, but how they exert these effects is largely unexplored. In C. elegans we recently disentangled a conserved vasopressin/ocytocin-related system that –as in humans– mediates associative learning. As such, we can deliver the experience, model and logical approach to provide detailed insights in neuropeptidergic control of learning and memory. We will first identify the endogenous ligand of all orphan C. elegans neuropeptide GPCRs, as this will provide the essential basis to build this project on. Mutants of neuropeptide-receptor pairs will then be tested for their ability to learn or maintain associative short- or long-term memory. We will also define in which cells and circuits relevant neuropeptides and receptors are needed for these functions, in order to generate models of neuropeptidergic control of learning and memory. We envisage the use of novel tools and cutting-edge experimental setups to take this research beyond its current horizon. Via single cell RNA sequencing, optogenetic analyses and in vivo calcium imaging, we will develop a workflow to build integrative models of associative learning and memory processes mediated by neuropeptides, which will serve as a scaffold for the study of these processes in more complex brains."