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. 2008 Jun;15(6):394–402. doi: 10.1101/lm.909208

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Copyright © 2008, Cold Spring Harbor Laboratory Press

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Figure 4. — Rat fear acquisition and within-session extinction learning for all immediate extinction (open circles) and delayed extinction (closed circles) groups. Rats were presented with 20 nonreinforced CS presentations in a novel context immediately following fear acquisition (immediate extinction) or 3 d following fear acquisition (delayed extinction). Both groups showed equivalent levels of freezing during the third acquisition CS (acq.) and freezing was low prior to the first extinction CS (pre). Immediate extinction rats generally froze less and extinguished faster than delayed extinction rats. For the acquisition time point: n = 30 rats/group. For the extinction session time points: n = 24 rats/group. Note that data were combined from the rat reinstatement experiment and spontaneous recovery experiment, since all animals within each group were treated identically through this phase. The data for four rats (two immediate extinction and two delayed extinction) were lost for the acquisition time point because of a recording error. *P < 0.05 compared with immediate extinction.