Living in a social environment requires extracting social information in a meaningful way, a process that involves the perception of socially relevant signals, representation in the brain and integration with prior experience, eventually leading to modulation of behavior. Understanding how the brain interprets the world requires us to integrate our understanding of genes, brain circuits and ongoing experiences that modify behavior. We are using Drosophila Melanogaster as a model organism to study the interplay between the social environment and the brain because of its accessibility to genetic and physiological manipulation as well as its complex behavioral repertoire. We have recently demonstrated that social experience in flies can modulate the way reward is perceived and in turn modulate reward-seeking behavior through regulation of the Neuropeptide F (a homologue of Neuropeptide Y). Our study suggests that activity of the NPF/NPF receptor axis represents the state of the fly reward system and modifies behavior accordingly. Modulation of the NPF system by socially rewarding and non-rewarding experiences may thus reflect a broader mechanism by which experience is represented in the brain and converted into changes of circuit function and, eventually, modulation of behavior. The goal of this proposal is to uncover the molecular and neural mechanisms by which rewarding and non-rewarding experiences are perceived, represented in the brain and converted into modulation of behavior. I will utilize genetic and molecular experiments, initially focusing on the NPF pathway as an inroad pathway, to dissect further the input and output components of this circuit using genetic intersection approach and identify the molecular representation of experience within NPF cells using cell specific transcriptome analysis. In addition we will use state of the art tracking and machine vision technologies to study the effect of social experience on social group dynamics.