Mapping and Deciphering Neural Codes of NMDA Receptor-Dependent Fear Memory Engrams in the Hippocampus
(A) Illustration of tone-shock trace fear conditioned memory. A 2-sec neutral tone precedes a mild foot-shock (0.3 sec) with a 20-sec time trace interval. Seven pairings were given. (B) Immediate freezing during learning and contextual freezing during 1-hr contextual memory recall. There was a significant difference in contextual freezing between the control (n = 4, 52%±6%) and mutant mice (n = 5, 21%±5%). Error bars represent SEM; *p<0.05. (C) Impaired trace fear retention in the mutant group as compared to the control group. Freezing prior to recall tone and after the tone at 1-hr trace recall in the control and mutant mice. The tone was presented for seven times (trials) with a 1–3 min random time interval. There was a significant difference in tone-induced freezing between control (51%±7%) and knockout mice (31%±4%), **p<0.01.