Interaction among the Hippocampus, Medial Prefrontal Cortex and Nucleus Accumbens during Formation of Affective Memory in Two Different Tasks.
Date Issued
2007
Date
2007
Author(s)
Chi, Yang Fang
DOI
zh-TW
Abstract
Evidence from our laboratory has shown that affective memory processing engages many brain regions. However, how information flows within this widely distributed neural circuit is unclear. The hippocampus (DH), medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) are implicated in processing affective memory. This study examined interaction among these regions during memory formation in two affective learning tasks. Male Wistar rats with chronic cannulae implanted in the DH, mPFC or NAc were trained on a one-trial step-through inhibitory avoidance task or a contextual fear conditioning task. Shortly after training, norepinephrine (NE) was given into one of the targets and 4% lidocaine was infused into another. Retention was tested 24 hrs after training. The results in inhibitory avoidance showed that infusion of 0.2 μg NE after training into DH enhanced memory and this effect was blocked by concurrent intra-mPFC infusion of lidocaine. Likewise, the memory enhancing effect of 0.1 μg NE infused into the mPFC was blocked by concurrent intra-DH infusion of lidocaine. In contextual fear conditioning, we found immediately posttraining infusion of 2.0 μg, but not other doses, of NE into DH or mPFC increased retention. However, the same treatment given 6 hrs after training had no effect on memory. These data suggest that NE infused into the DH and mPFC had dose- and time-dependent effects in memory consolidation of contextual fear conditioning. Furthermore, in contextual fear conditioning, the memory enhancing effect of NE given to the DH was blocked by simultaneously infusing lidocaine into mPFC and vice versa.
These findings suggest that during memory formation the DH and mPFC either form a reverberating circuit or send convergent inputs to a third target, such as the NAc. The latter possibility was favored by the findings in the inhibitory avoidance task that NE at sub-enhancing doses induced robust enhancement if simultaneously given into both regions. In contrast, results from the contextual fear conditioning showed that infusing sub-enhancing doses of NE into DH and mPFC simultaneously induced no additive effect. It implies that in this task information flow may form a reverberating circuit. A following-up experiment showed that the memory enhancing effect of NE infused into the DH or mPFC was blocked by inactivating the NAc with lidocaine in the inhibitory avoidance task, but not in the contextual fear conditioning task. These findings, taken together, suggest that NE in mPFC and DH during an inhibitory avoidance task modulated memory formation processes via the convergent inputs to the NAc, but they formed a reverberating circuit without engaging the NAc during formation of contextual fear memory.
Subjects
情緒記憶
穩固歷程
抑制型躲避學習
情境恐懼制約
正腎上腺素
emotional memory
inhibitory avoidance task
contextual fear conditioning task
norepinephrine
Type
other
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