Table 1.
Definition of different behaviors in the Resident Intruder test.
| Behavior | Definition | Measure |
|---|---|---|
| SOCIAL INTEREST BEHAVIOR | ||
| Approach | Directed movement toward the other mouse at a walking or running pace until the distance between both mice is at most one body length. | Number |
| Nasal sniffing | The mouse contacts the nasal region of a conspecific with the twitching tip of its snout. | Duration |
| Anogenital sniffing | The mouse contacts the anogenital region of a conspecific with the twitching tip of its snout. | Duration |
| Following | The mouse runs after the other mouse, while the head of the following mouse is directed at the backside of the other individual. The maximum distance between the animals is one body length. After stopping forward motion for at least 3 s, additional following is considered a new event. | Duration |
| AGONISTIC BEHAVIOR | ||
| Attack | A mouse contacts the body of the other mouse with its mouth, making that mouse react with winced movements of single extremities, the tail, or the whole body. Attacks are single countable events of low intensity. | Number |
| Attack latency | Time that elapses until attacking is performed for the first time by the focal animal. If no attacking occurs, the latency is set to the maximal testing time of 10 min. | Duration |
| Sustained attack | A series of attacks with rushing and leaping of the other mouse. As the behavior is of higher intensity than the attack itself, single attacks are not discriminable. | Number |
| Escalated fighting | Physical struggle between two mice, initiated by an attack and usually involving further attacks, kicking, wrestling, and rolling in the bedding. | Number |
| Chasing | ‘Following’ subsequent to an agonistic interaction (attacking, sustained attacking, or escalated fighting). | Duration |