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Factors regulating the effects of hippocampal inactivation on renewal of conditional fear after extinction - PubMed

Comparative Study

. 2004 Sep-Oct;11(5):598-603.

doi: 10.1101/lm.78704.

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Comparative Study

Factors regulating the effects of hippocampal inactivation on renewal of conditional fear after extinction

Kevin A Corcoran et al. Learn Mem. 2004 Sep-Oct.

Abstract

After extinction of fear to a Pavlovian conditional stimulus (CS), contextual stimuli come to regulate the expression of fear to that CS. There is growing evidence that the context dependence of memory retrieval after extinction involves the hippocampus. In the present experiment, we examine whether hippocampal involvement in memory retrieval after extinction is related to the history of CS presentations in the context used for retrieval testing. We used infusions of muscimol to inactivate the dorsal hippocampus (DH) during postextinction retrieval tests that were conducted in contexts that differed in their history of CS presentations in that context. We found that DH inactivation affected the context-dependent retrieval of extinction (i.e., renewal) when testing occurred in a context that had no history of CS exposure, but not in a context that reliably predicted the CS. These results are discussed in terms of theories regarding the role of the hippocampus in contextual memory retrieval.

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Figures

Figure 1
Figure 1

Cannula placement in the dorsal hippocampus. Photomicrograph showing a thionin-stained coronal section from the brain of a rat with representative cannula placements in the dorsal hippocampus.

Figure 2
Figure 2

Illustration of injection cannula placements in the dorsal hippocampus. Placements represented are from all rats included in the final analysis (CON/SAL, •; CON/MUS, ○; INCON/SAL, ▪; INCON/MUS, □). Atlas templates adapted from Swanson (1992).

Figure 3
Figure 3

Extinction to the tone CS. Mean (±SEM) percentage of freezing for the first five CS presentations across the 5 d of extinction in contexts A and B. The group labels refer to the treatment conditions that would later be imposed during retrieval testing (not during extinction training). Data were not collected on day two of extinction due to a technical problem.

Figure 4
Figure 4

Hippocampal inactivation disrupts renewal of fear in contexts that are uninformative as to the meaning of the CS. Mean (± SEM) percentage of freezing during the first minute after CS onset during testing. Rats were tested either in the same context in which extinction took place (CON, open bars) or in the context in which no CS-alone presentations were given during the extinction phase of training (INCON, filled bars). Data are separated by whether rats were tested in a context with an ambiguous history of CS presentations (AAA/AAB renewal; left) or in an unambiguous context (ABA/ABB renewal; right).

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References

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