To most effectively isolate the contribution of the hippocampus to context fear learning, we utilized a trace fear conditioning protocol45. In brief, mice were acclimated to and handled within the testing room for 2 d prior to testing. For the training session (Day 1), mice were placed in fear conditioning chambers (Med Associates, Inc.; St Albans, VT) with metal bar floors and white wall insert that were cleaned with 75% ethanol. A 30-s white noise (65 dB/3 kHz) was used as the conditioned stimulus (CS, cue), and a 2-s footshock (0.50 mA) was used as the unconditioned stimulus (US). Training consisted of 2 CS-US pairings in which the US was delivered 30 s after the end of the CS; CS presentations were separated by 90 s (7.5 min total conditioning time). On Day 2, the level of contextual fear learning was assessed by returning mice to the training chambers and measuring freezing behavior for 5 min. On Day 3, the chambers were reconfigured (i.e., floor bars were covered with a plastic insert and white wall inserts were replaced with black
