Immediate extinction deficit. A, Percentage of freezing during conditioning. Rats were given five CS–US conditioning trials. All groups exhibited a similar increase in freezing across trials. B, Percentage of freezing during extinction training. The immediate extinction group (I-EXT) and the delayed extinction group (D-EXT) received 15 CS-only trials, 15 min and 24 h after fear conditioning, respectively. Both groups showed similarly attenuated freezing at the end of the extinction training. The immediate no-extinction group (I-NO-EXT) and the delayed no-extinction group (D-NO-EXT) were placed in the extinction context for the same amount of time but without CS presentation at the corresponding time points. All tests were performed in a novel context. C, Averaged percentage of freezing across three test trials. The D-EXT group showed significantly lower freezing relative to the other groups. *p < 0.05. All data are presented as means ± SEM.