Novel Object Recognition (NOR) Test

The NOR test was performed to assess non-spatial memory in a 25 cm × 25 cm × 25 cm and black soundproof box (Zhu et al., 2014). The test consisted of three phase: habituation, training, and retention sessions. In the first stage, the single mouse was placed into the box facing the wall, having a preceding 10 min habituation once a day, for 3 consecutive days. During the training session, two indistinguishable objects were symmetrically fixed to the floor of the box, and each mouse was allowed to travel in the apparatus freely for 10 min. After the training, the mice were immediately returned to their home cages for 60 min at least. Ultimately, during the retention test, each mouse was placed back into the same box, with one of the familiar objects substituted by a novel object. Test mouse was then allowed to freely explore for 5 min and videotaped. New object recognition index, a ratio of the amount of time spent exploring the novel object over the total time spent exploring the both, was used to evaluate cognitive function. A mouse was scored as exploring the object when touching or sniffing the object with its nose or front legs, and facing the object at a distance within 1 cm (Wang D. et al., 2018).