大鼠內側前額葉皮質參與似情節記憶的編碼歷程

The Medial Prefrontal Cortex in Rats Contributes to the Encoding Process of Episodic-Like Memory

許多研究者認為，情節記憶的編碼過程可以視為快速且有彈性地連結各項記憶元素。在這一歷程中，語意元素被提取出來並與當時發生的時間和地點重新組織成一個事件記憶。在動物實驗中，似情節記憶定義為，將記憶中的空間和時間元素與特定事件整合之能力。先前研究發現，內側前額葉皮質被破壞後，大鼠失去對恐懼制約事件形成似情節記憶的能力。然而，內側前額葉皮質如何參與此一記憶編碼歷程？許多細節仍然未知。故我們在本研究中，選擇了幾個似情節記憶編碼歷程中的不同時間，讓大鼠內側前額葉皮質暫時失去活性，並觀察恐懼制約事件的似情節記憶如何被影響。結果我們發現，若內側前額葉皮質是在前探索階段時失去活性，並不會干擾時間與空間的配對形成。相反地，在足部電擊前失去活性則會損害形成恐懼制約事件的似情節記憶。此外，後續實驗排除了作業表現的損失來自於巴夫洛夫恐懼制約能力受損。這結果支持情節記憶的編碼歷程是記憶元素的重組，而內側前額葉皮質在其中扮演了一個重要的角色。

The encoding process of episodic memory is considered by many researchers as a rapid formation of flexible associations, in which semantic elements are retrieved and reorganized in a unique temporal and spatial context. In animal studies, episodic-like memory is defined as the ability to remember what happened where and when. A previous study showed that rats with lesions of medial prefrontal cortex (mPFC) failed to form an episodic-like memory for a fear conditioning event, indicating that the mPFC might play a crucial role. However, details about how mPFC is involved in the encoding process remain unknown. In this study, we temporarily deactivated mPFC of rats at different time points during the memory encoding procedures, and observed how the episodic-like memory of a fear conditioning event was influenced. We found that mPFC deactivation in the preexposure phase didn't interfere with the formation of time-context paired associations, while manipulation before foot-shock impaired the episodic-like memory. Subsequent experiments excluded the alternative interpretations that temporary mPF C deactivation impaired the more basic Pavlovian fear conditioning. The results are consistent with the idea that episodic encoding is a reorganization of mnemonic elements, in which mPFC is involved.