Is Witnessing Stress the Same as Experiencing It?

A diagnostic criterion for post-traumatic stress disorder (PTSD) is witnessing another person's severe stress. To determine whether this criterion has a neurobiological basis, researchers exposed mice to 10 daily sessions of physical stress (PS; caged with a larger, more aggressive mouse) or emotional stress (ES; placed in cages adjacent to the PS sessions).

At both 24 hours and 1 month after stress exposure, PS and ES mice exhibited similar elevations of corticosterone levels compared with nonexposed controls. One day postexposure, PS mice (and ES mice to a milder degree) interacted less with strange mice (i.e., showed social avoidance). A month later, social avoidance was diminished to a similar level in PS and ES mice. However, removing s…