Intruder Exposure Behavior Protocol

The test was conducted as previously described (Santangelo et al. 2016 (link)). Briefly, the subjects were separated from their partner and divided into the right-hand upper quadrant of the home cage (separated phase, Fig. 2A). The subject’s behavior was recorded using a GoPro camera and a Sennheiser MKE 400 microphone, which were placed at a short distance from the cage (Fig. 2B). After 8 min, an unfamiliar experimenter, the “HI,” entered the room and stood 40 cm away in front of the cage. The HI was disguised using a realistic looking human mask (Masks Direct) and wearing familiar scrubs and gown. When possible, the intruder made direct eye contact with the subject for 2 min (intruder phase). The intruder then quietly left the room, and the subject’s behavior was recorded for a further 5 min (postintruder phase).