Open field and light–dark activity within each 10-minute test for 8-month timeframe, shoebox cages.

Values = mean ± SEM. Sexes were combined (N = 33–36).Individual mice were placed in the arena and monitored for 10 minutes for each test.Duplex cages were not tested. Strains 129/S1/SvImJ and A/J are not included in light–dark testing because these mice did not venture from the dark enclosure.aFor details of floor space for each density group, see Table 1.Behavioral observations did not differ significantly among density groups, but they did differ among strains.