FIG. 2.

Lateral mFPI impairs extinction and memory for extinction. (A) Timeline for contextual fear and extinction training and testing. Rats received a lateral mild FPI (or sham operated); 4 weeks later, animals were trained in a one-trial context fear conditioning task. Twenty-four hours after training, memory was assessed. Fear memory extinction was carried out 24 h later. Memory of the extinction was tested 24 h later. Freezing behavior (percent time spent freezing) was used as an indicator of fear. (B) Both sham and mFPI animals showed similar freezing behaviors during the period of context fear testing, an indication that mFPI does not impair context fear memory. (C) During extinction training, sham-operated rats learn that the context does not predict the footshock, as indicated by reduced freezing over time. mFPI animals displayed enhanced freezing behavior throughout the extinction training period, indicating impaired extinction learning. (D) When tested for extinction memory, sham animals displayed reduced freezing indicating memory for the extinction learning. In contrast, mFPI animals displayed significantly enhanced freezing, indicating impaired memory for the extinction training. Data are mean ± standard error of the mean. *Significant difference between sham and mFPI by t-test. ^‡Significant difference between sham and mFPI by repeated-measures two-way analysis of variance. mFPI, mild fluid percussion injury.