As in the elevated-plus maze, this test is based on two conflicting innate tendencies: exploring a novel environment and avoiding elevated and open spaces constituting situations of predator risk. The apparatus consists of two open (stressful) and two enclosed (protecting) elevated arms that form a zero or circle. Time spent in exploring enclosed versus open arms indicates then the anxiety level of the animal. When placed into this apparatus, naïve mice and rats will, by nature, tend to explore less the open arms due its natural fear of heights and open spaces. In this context, anxiolytics generally increase the time spent exploring the open arms and anxiogenics have opposite effect, increasing the time spent into the closed arms.