In the latest study, the researchers paired sets of mice together and then removed one mouse from each pair and subjected them to a mild amount of stress. They then returned the stressed mouse to the pair and observed the brains of both mice. The results showed that the stressed mouse experienced changes in a group of neurons located in the hippocampus, a brain area that plays a central role in memory and emotional response. The brain of the other mouse that hadn’t been stressed, but was now in the presence of its stressed partner, rapidly showed the same neuronal changes in its hippocampus. In effect, the brains of the unstressed mice mirrored the brains of the stressed mice.