Project Summary One of the most crucial functions of an organism's nervous system is the ability to form long-term memories. However, the molecular mechanisms underlying long-term memory formation have yet to be fully elucidated, due to the fact that memory is a complex process requiring a coordinated response across multiple neuron types and brain regions. Moreover, it is unknown how these essential memory components contribute to variability in individual memory performance, which is particularly prominent in the context of age-related memory loss. Identifying the molecules involved in these processes is important not only to gain insight into normal brain function but can also lead to an understanding of disease states such as age-related cognitive decline, neurodevelopmental disorders, and Alzheimer's disease. A major barrier to identifying the molecular regulators of long-term memory is the sheer complexity of the mammalian nervous system; therefore, we propose to use the invertebrate model C. elegans, in which all neurons and synaptic connections in the organism are already known, to molecularly “define memory.” Here we propose to combine a number of cutting-edge techniques with behavior in this simple system to generate the most precise snapshot to date of the nervous system-wide molecular changes that are necessary for memory formation. In Project 1, we will combine behavioral training, spatial transcriptomics, new techniques that we have developed to simultaneously profile transcriptomes of somatic and synaptic subcompartments, and temporally and spatially precise gene manipulation to reveal the most complete molecular snapshot of mechanisms necessary for memory formation to date. In Project 2, we will use unbiased behavioral profiling to uncover strategies of variability in memory performance, which we will used to predict individuals likely to exhibit improved memory performance with age. We will then use epigenomics and genomics techniques to determine which essential memory components may regulate individual memory performance, followed by functional validation in the context of age-related memory loss. Combined, the proposed work will not only advance our understanding of one of the fundamental questions in the field of neuroscience but will also reveal new pathways that may be disrupted in neurological disorders, along with new targets for the development of therapies that prevent disrupted memory due to neurological disease.