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. 2015 Mar 31;9:91. doi: 10.3389/fnins.2015.00091

Figure 1.

Figure 1

Intelli-Cage-based competition task protocol. (A) An IntelliCage apparatus comprising a large cage [55 × 37.5 × 20.5 cm (w × d × h)] equipped with four corner chambers [15 × 15 × 21 cm] controlled by a computer. Each of these chambers holds two water bottles and functions as a fully automated operational unit. A radiofrequency identification (RFID) device reader is located at the entrance of each chamber and enables the IntelliCage software to record the entry and exit time of each individual resident mouse, given that all resident mice have been tagged by the subcutaneous implantation of RFID microchips. An entry to each chamber is physically restricted to a single mouse at any given time. Inside the chamber, there is a motorized door in front of each water bottle nozzle. The opening and closing of the door are programmable and can be uniquely assigned for each mouse. For instance, the door can detect the nose poking behavior of a mouse, which can be used to initiate opening, and closing can be programmed by time. (B) Mice are deprived of water throughout the day, except during the session period between 2200 and 0100 h. Session periods are cued by an LED light on the wall of the IntelliCage, and mice are thoroughly trained to learn the cue. (C) Inside the chamber, a mouse uses its nose to poke either of the two doors to open it for accessing the water nozzle. The activated door is programmed to stay open for 4 s. After the door shuts, the chamber becomes inactivated for that mouse, which must go to a different corner chamber for another reward. The task protocol is thus programmed to prevent any single mouse from persistently occupying one corner chamber for an indefinite time. The occupancy of the corner chambers is measured by dwell time or visit frequency. (D) The experimental group composition as well as the degree of competition can be flexibly determined by adjusting the density of animals within an apparatus. Assessment of the motivation level toward reward can be achieved by dividing the dominants and subordinates into two separate cages for several days. If their visiting patterns overlap, it may be regarded as a clear indication that the motivation of the subordinate mice for drinking water is not different from that of the dominants. After the motivational level of the subordinates has been confirmed, all the mice can be combined again to confirm whether the peak number of visits in the subordinates declines once again.