Diagram of Experimental Design.

<p>We designed a two-day experimental protocol where mice were randomly assigned to one of four experimental groups: (1) SH_obs = observers that received footshocks in context A on day 1, and then witnessed footshocks given to a subject in context B on day 2, n = 15. (2) SHN_obs = observers that received footshocks in context A on day 1, and then witnessed a subject in context B, where footshocks were not delivered on day 2, n = 15. (3) SW_obs = observers that underwent forced swim stress on day 1, and then witnessed footshocks given to a subject in context B on day 2, n = 13. (4) Naïve = observers that remained in their homecage on day 1, and that witnessed footshocks given to a subject in context B on day 2, n = 17.