Context-dependent auditory fear conditioning.

<p>(A) Procedure used for conditioning (i) and measurement (ii). (i) In the conditioning session, 4 silent and 3 noise conditions were prepared, and were sequentially alternated. In a silent-condition block, only a conditioned stimulus (CS) consisting of a 20-kHz tone was presented 10 times. In a noise-condition block, a white noise stimulus was continuously presented during the block, and an unconditioned stimulus (US) consisting of an electrical foot shock was associated with the CS 5 times. The total time of the conditioning session was approximately 2.5 h. (ii) The measurement of freezing time of rats was conducted the day after the conditioning session. CS only, noise only, and CS under noise were presented in order each for 3 min. (B) Freezing times of rats. Asterisks indicate the significance of post-hoc analyses (Mann-Whitney U-test: **, p<0.01).