Acclimation & testing periods
Vendor Male mice (8–11 per strain) obtained from The Jackson Laboratory (JAX®), Bar Harbor, ME, USA) at 3–5 wks of age. Ages Mice were 32–46 days old at the start of operant training, such that the experiment quickly was completed to prevent the data being affected by progressive hearing loss in some strains (BALB⁄ cJ, C57BL⁄ 6J, C57L⁄ J, CBA⁄ J, DBA⁄ 2J; auditory brain response threshold data for mice younger or older than 12 weeks. Testing was completed before mice reached 3 months of age. Feed & water The first day of operant training occurred after a minimum of 48 hrs on a food restricted diet (approximately 2 g of mouse chow per day per mouse), and mice were maintained at approximately 90% of age-adjusted free-feeding weight with mouse chow throughout the experiment. This minimal level of food restriction provided motivation for sucrose responding in the Go ⁄ No-go task. Housing Mice were housed 2–5 per cage Photoperiod 12:12-h light: dark cycle (lights on at 6 am) Temperature 21.7 ± 1°C Regulatory compliance Mice were maintained according to guidelines provided by the Oregon Health & Science University Department of Comparative Medicine. The Institutional Animal Care and Use Committee approved all procedures.