For some of these IEGs, like CREB, Homer1a, and ΔFosB, evidence abounds for their roles in stress responses, multiple aspects of mood disorders, drug addiction, and even antidepressant treatment, and the challenge now lies in integrating their functions across the brain regions and cell types involved and determining their downstream targets in order to uncover potential novel drug targets. This evidence concerns the gene HOMER1 and mood disorder.