Figure 1.

Mean (±SEM) freezing level during training, context test, and tone test. In the training, 1, 2, and 3 denote 3 min of baseline (pretone footshock) and 4, 5, and 6 represent three posttone footshock intervals. The context test was for 8 min. In the tone test, 1 and 2 signify 2 min of baseline (in a new context) prior to 6 min of tone onset. Freezing scores are expressed as the percentage of total observation.