To better characterize potential impacts of prior aversive experience on EPM performance a series of experiments were carried out that systematically varied the time since stimulus presentation and the modality of the conditioning stimulus. Furthermore, we examined whether the EPM measurements taken days before or after threat conditioning measurements held any relationship. MATERIALS AND METHODS: Subjects. Subjects were 104 adult male Lister-Hooded rats (Charles River and Envigo, UK) weighing approx. 250–300g at the start of experiments. All animals were housed in groups of four per cage and kept under a reversed 12 h light/dark cycle (lights off 07:00 h until 19:00 h) and were provided with food and water ad libitum, except for during behavioral procedures, which were conducted during the rats’ dark cycle. The rats were randomly assigned to each group and experimenters were blind to group allocation for subsequent analysis. This research was conducted on Project Licence 70/7548 and has been regulated under the Animals (Scientific Procedures) Act 1986 Amendment Regulations 2012 following ethical review by the University of Cambridge Animal Welfare and Ethical Review Body (AWERB). See materials and methods for full details.