Fig. 2

Cued fear extinction 1 and 2. The % freezing value to the tone during extinction phases 1 and 2 at 12 weeks of age（n＝5）. The data were pooled into 4（extinction 1） and 8（extinction 2） bins. A bin is the average of 5 trials of extinction. All data points are the means±SEM. *p＜0.05 and **p＜0.01 indicate a statistically significant difference from the first bin（the first 5 trials） of extinction phase 2.