杏仁核在酬賞與逃避學習作業之角色： 從神經元活性變化探討情緒記憶的穩固與提取

Abstract

杏仁核被認為是處理恐懼及焦慮記憶的重要神經結構，但其在處理酬賞行為上亦扮演重要角色，因此，杏仁核內的神經單元如何表徵正向與負向的情緒記憶成為一值得探討的議題。本研究利用抑制行逃避作業及酬賞所引發的地點偏好作業來探討此議題。在實驗一至實驗三於行為作業的訓練階段之前或之後給予河豚毒素抑制杏仁核的活動，或是於行為學習作業前毀除杏仁核，結果顯示壓抑或毀除杏仁核會有礙於兩項作業的學習。在實驗四中，我們進一步紀錄杏仁核在此兩項學習作業階段中神經元活性的變化，實驗結果顯示，在學習階段後，杏仁核內部分神經細胞分別表現出興奮性或是抑制性神經活動的變化，其中部分細胞甚至於學習階段後並經過一段等待時間才開始表現出神經細胞反應的變化。同時，在學習階段後亦發現杏仁核內神經細胞的反應變化有側化的現象。在學習測試階段中，雖然只有少數神經細胞表現出反應活性的改變，但這些神經細胞分別只對抑制型逃避作業或是酬賞作業表現出反應活性的變化，這顯示正向與負向情緒刺激分別由杏仁核內兩群不同的神經細胞負責處理。本研究證實正向或負向的情緒經驗記憶處理都需要杏仁核細胞的參與，但是正向與負向情緒經驗分別涉及不同的細胞。

The amygdala is well documented to mediate defensive behavior under fear and anxiety, but its role in appetitive behavior may be just as important according to the literature. A question arises whether the amygdala codes positive and negative stimuli in the same or different population of neurons. This study addressed this issue by examining involvement of the amygdala in an inhibitory avoidance task and a reward place preference task. In the first three experiments, we suppressed or lesioned the amygdala by microinfusion of tetrodotoxin or ibotenic acid before or after training on either task and verified that the amygdala was required to learn both tasks adopted. In the fourth experiment, the single unit activity was recorded from amygdala neurons at various phases of the two tasks we designed. It was shown that while some neurons responded with excitation or inhibition immediately after either one of the two tasks, other neurons did not change their firing rate unit a delay period of time. Furthermore, lateralized activation of the amygdala was detected after training. In the retention period, the individual responsive neurons also changed their firing rates either in the reward test or in the avoidance test and few neurons responded to both the reward and the avoidance tasks. Thus positive and negative stimuli were processed by two distinct populations of amygdala neurons. These findings shed lights on how the amygdala neurons represent various kinds of emotional experience.