and volume, but different shape and appearance. The mouse was again placed in the chamber to explore the objects for 3 min. The animal was considered to be exploring the object if its head was directed at the object and the distance between the object and the mouse nose was 1 cm or less. The amount of time spent exploring each object was recorded and evaluated by operators blinded to genotype. The positions (left or right) of the ‘new’ and the ‘familiar’ objects during the testing phase were counterbalanced between mice and sessions. The discrimination index was computed as R = Tnew*100/(Tnew + Told), were Tnew is the time spent exploring the new object, and Told is the time spent exploring the familiar object.
