Mice that suffer unpredictable chronic mild stress (UCMS) show symptoms that look like depression in humans. Researchers were thinking that deficits in hippocampal neurogenesis (the birth of new nerve cells) might be the cause of depression. Crusio and collaborators did experiments to look at changes in behavior and neurogenesis in stressed mice. They showed large changes in levels of aggression, anxiety, depressive-like behaviors, and learning. At the same time, there was a large drop in neurogenesis. The results dependent very much on the strain and sex. There did not appear to be a clear-cut correlation between the different changes. They concluded that their data do not support the idea that deficits in hippocampal neurogenesis alone are the cause of depression. However, they do not disprove this hypothesis either.