Figure 11.

Effects of tone presentation before conditioning on the freezing response to the tone. (A) Animals were randomly assigned to four groups. Naive mice of group I were repeatedly exposed to a 3-min tone of 98 dB in test context 1 at d1 and d7. Animals of group II were pre-exposed to the 3-min tone (80dB) in test context 1, followed by conditioning with a single 0.70-mA footshock at d0 and re-exposure to the 3-min tone the next day (d1). Mice of group III were exposed to the tone in test context 1 at d1 and d7 following conditioning. Mice of group IV were treated identically to group II, except for the tone intensity during tone pre-exposure at d-6 (95 dB instead of 80 dB). Note that group I is identical to group 98 dB of Figure 4B, group III with group 0.70-1 of Figure 4D, and group IV with group 95 dB of Figure 4B. (B) Reduced freezing to a loud tone on repeated tone presentation in naive mice (group I). (C) Reduced freezing to the tone on repeated tone presentation in conditioned mice (group III). (D) Pre-exposure to the tone led to a significantly reduced freezing response at d1 following conditioning (groups II and III). (E) The freezing response of group II at d1 was identical to that of group III at d7. (F) Pre-exposure to a loud tone had significantly less effects on freezing to the tone at d1 following conditioning than pre-exposure to a tone of the same intermediate intensity as used for conditioning and re-exposure to the tone at d1 (groups II and IV). For description of symbols and codes, see Tables 1 and 2. Data were analyzed in 20-sec bins and normalized to the length of the analysis interval. Mean ± SEM. (n = 10 per group). (^*) P < 0.05; (^***) P < 0.001 vs. the other group (2-way ANOVA for repeated measures, followed by Newman-Keuls post-hoc test).