In the study, the researchers stressed out several mice by periodically putting a much more aggressive mouse into their cage. After six days of exposure, the stressed mice could no longer recall the location of a hole to escape a maze, which they remembered easily before the stressful period began. "The stressed mice didn't recall it. The mice that weren't stressed, they really remembered it," said Jonathan Godbout, a neuroscience professor at Ohio State University and one of the study authors in a press release. For four weeks after the trauma, the mice continued to cower in corners, the mouse equivalent of social avoidance, a major symptom of depression.