Considering inflammation has helped neuroscientists cast a broader net when searching for causes of and possible treatments for mental illness, mood disorders and neurodevelopmental conditions. Last time you had a bad cold, you likely had less energy than usual. You lay around and didn't have any enthusiasm for your usual activities. After it dragged on for a day or two, a sense of helplessness probably set in. It was hard to remember what feeling good felt like or how you could ever bound off the couch again. In short, for a few days, you probably felt a lot like someone with depression.