RESUMEN
When using in-group and out-group faces as conditional stimuli (CS) in fear conditioning designs, extinction learning is selectively impaired for out-group faces. Additionally, stress seems to inhibit extinction retrieval leading to a higher return of fear, which might be especially the case for out-group faces. To test this hypothesis, 51 healthy women underwent fear acquisition training, consisting of repeated presentations of two in-group and two out-group faces. One of each (CS+) was paired with an electrical stimulation (unconditional stimulus, UCS), whereas the other was not coupled with the UCS (CS-). During immediate extinction training, all CS were presented again. On the next day, a retrieval and reinstatement test took place after a stress or a control procedure. Confirming previous research, impaired extinction learning occurred for out-group relative to in-group faces. During the reinstatement test, stress specifically increased responding towards the out-group CS-, thus reducing its safety signaling properties. So, stress seems to reduce the ability to adequately distinguish threat and safety cues after aversive experiences mimicked by reinstatement shocks.