In Experiment 4, activity was assessed using 16 automated monitors (AccuScan Instruments,Columbus, OH) with one mouse per chamber. The boxes (40 × 40 × 30 cm high) wereconstructed of clear plastic and confined within ventilated light- and sound-attenuatedcabinets [48]. An internal light source (3.3 W incandescent bulb) was used to maintain thelight cycle to which mice had been acclimated. During test sessions, activity was monitoredfrom grids of 8 × 8 infrared beams affixed 6 cm above the test chamber floor (breaks forvertical movements) or 2 cm above the floor (breaks for horizontal movements). Theprimary sample duration for the activity monitoring software was defined as a 15-min epoch,across 132 epochs, for a total session length of 33 h. Each 15-min epoch was furthersummed into 1 h bins for analysis, because initial examination showed that the data weresimilarly represented by these shorter and longer time phases. Data were summed acrosstime periods of interest before being analyzed, as described in the Results section.