Fig. 2.

Animals received either a distractor or no distractor during training. On the testing day, animals were presented with the tone and the light, or vice versa. (A) Percent time spent freezing during tone testing. The distractor during conditioning selectively disrupts trace learning, without affecting delay learning. An asterisk indicates significant reduction in time spent freezing for the distractor group compared with the nondistractor group of trace conditioning training (P < 0.05). Both delay and trace conditioning are significantly different from the shock-only conditioning for the nondistracted animals (black bars, P < 0.05). Error bars indicate SEM. (B) For light testing, there is no difference in percent time spent freezing between the animals that did and did not receive the distractor during training. (C) Six groups of mice received one to six tone–shock pairings and the flashing light as the distractor during trace conditioning. One group of mice received standard six tone–shock pairings and no distractor during trace conditioning. There is no difference in freezing to the flashing light for any of the six tone–shock pairings, compared with mice that received no flashing light. As a positive control, the ND group shows a high level of freezing in the tone test. TS, tone–shock pairing; ND, no distractor. (D) No difference was observed between the distractor and no distractor groups, indicating that the distractor did not affect contextual fear conditioning. (E) No difference was found in locomotor activity, as assessed by the number of crossing and rearing events between the distractor and no distractor groups.