Figure 6.

Failure to recall extinction was associated with increased prelimbic tone responses. A, Rats were divided into two subgroups based on the degree of extinction recall: rats showing good extinction recall (low-fear, <50% freezing in the first two trials; n = 8) and rats showing poor extinction recall (high-fear, >50% freezing; n = 7; **p's <0.01). No significant group differences in freezing were detected in conditioning and extinction training. B, Magnitude of tone responses at the recall phase in the two subgroups (9 tone-responsive neurons in each subgroup). High-fear rats showed larger PL tone responses at recall than low-fear rats, suggesting that PL activity contributed to impaired extinction recall (*p = 0.046). C, Percentage of tone-responsive neurons at different phases of the experiment. Only neurons maintained throughout all phases were considered for this analysis (low-fear, n = 32; high-fear, n = 19). Compared with low-fear rats, high-fear rats showed a higher percentage of tone-responsive neurons at recall, as well as during conditioning and early extinction.