Contextual and Cued Fear Conditioning in Mice

Mice were tested in individual conditioning chambers. The VideoFreeze system (Med Associates) was used to assess behavior as described previously (Anagnostaras et al., 2010 (link); Carmack et al., 2014 (link)). Training consisted of one 10-min session. Mice were placed in chambers and baseline activity was assessed for 2 min. Mice then received three tone-shock pairings beginning at minutes 2, 3, and 4. Tone-shock pairings consisted of a 30-s tone (2.8 kHz, 90 dB) that co-terminated with a 2-s scrambled AC foot shock (0.75 mA, RMS). Twenty-four hours post-training, mice were returned to the training context. Once mice were placed in the chambers, freezing was measured for 5 min to assess fear to the context. Twenty-four hours after the context test a 5 min tone test was conducted to assess cued memory. The context was altered on multiple dimensions. White acrylic sheets were placed over the grid floors, a black plastic triangular insert was used to alter wall shape, and chambers were cleaned and scented with a 5% vinegar solution. Near-infrared light was used, in the absence of white light, to create a dark environment. The test consisted of a 2-min baseline period followed by the presentation of three 30-s tones (2.8 kHz, 90 dBA) at minutes 2, 3, and 4. The tones matched those used during training.