All female subjects completed study sessions about 1 week prior to menses onset (based on self-reports of last period and cycle length), to insure that they were studied while estrogen levels were low. This restriction was based on evidence that high estradiol levels can facilitate fear extinction (Milad et al., 2010; Zeidan et al., 2011). All participants gave written informed consent after explanation of the experimental protocol, as approved by the University of Michigan Institutional Review Board.
