Abnormal reward and threat processing are key players in psychiatric conditions such as eating disorders, addiction or depression. These functions are strongly regulated by the nucleus accumbens shell (NAcSh) which integrates emotional signals to regulate motor output. Historically the NAcSh was thought to consist of 2 pathways: dopamine 1 and 2 receptor-expressing striatal projection neurons (D1, D2-SPNs) which promoted reward and aversive behavior, respectively. Yet recent work has revealed that both cell types can promote either reward or aversion, depending on the NAcSh subregion or input/output patterns. Hence more work is needed to chart a full functional map of this brain region. Here we first address how anterior vs. posterior NAcSh subregions differentially regulate behavior, focusing on D1-SPNs. We combine neuroanatomical tracing, in vivo fiber photometry and optogenetics to identify potential diverging points as to how anterior vs. posterior medial NAcSh D1R-SPNs might project to different target brain regions, differentially encode behaviorally-relevant stimuli and in turn regulate behavior. Furthermore, recent studies have revealed the large transcriptomic diversity of NAcSh cells. What still remains unclear is how newly identified molecular cellular subtypes relate to the NAc’s functional anatomy. We leverage public scRNAseq datasets to characterize a molecularly-defined NAc subcircuit. By the generation of a new Flp-driver mouse line, together with fluorescent in situ hybridization, neuroanatomical tracing and in vivo fiber photometry, we characterize a unique NAcSh cell type in the medial NAcSh. This builds the basis for future work to manipulate NAcSh subcircuits in clinically-relevant models for psychiatry.