ISSN : 1226-9654
공포학습에서의 편도체의 역할에 대해서는 공포기억이 편도체 내에 저장된다는 견해와 편도체가 뇌의 다른 부위에 공포기억이 저장되는 과정을 조절한다는 견해가 대립하고 있다. 전자 입장의 연구들은 주로 고전적 공포조건형성 과제를, 후자 입장의 연구들은 주로 회피학습, 즉 도구적 조건형성 과제를 사용하여 서로 상충되는 증거들을 제시해왔다. 동물의 반응과 상관없이 자극들이 제시되는 고전적 조건형성과는 달리 회피학습에서는 특정 자극에 대한 공포뿐 아니라 그 자극을 회피하기 위한 운동반응이 습득되어야 한다. 따라서 회피학습 시에 공포기억은 편도체 내에 저장되지만 회피반응을 위한 운동기억은 편도체 이외의 부위에 저장될 가능성이 있다. 그럴 경우 회피학습 후 기억검사 전에 편도체를 불활성화시키면 조건공포의 표현은 방해받더라도 능동회피반응의 수행은 영향을 받지 않을 것이다. 따라서 본 연구는 편도체에 안내관을 심어놓은 쥐들(Sprague-Dawley, 수컷)에게 불빛을 경고자극으로 사용하여 양방향 능동회피학습을 매일 30회씩 3일 동안 시켰다. 다음날, 편도체에 muscimol (4.4 nmol/0.5 ul) 또는 용매를 주입하고 난 직후, 쥐들을 활동성 검사상자에 넣고 불빛에 대한 조건공포를 검사하였다. 이틀 후, 역시 편도체에 muscimol 또는 용매를 주입한 후 능동회피반응을 재훈련시켰다. 그 결과, muscimol 주입에 의한 편도체 불활성화는 조건공포의 표현은 방해했지만 능동회피반응의 수행은 방해하지 않았다. 동일한 동물에게서 편도체 기능의 차단이 두 종류의 기억의 인출에 서로 다른 효과를 가진다는 이 결과는 위의 두 이론의 상충되는 주장을 설명해 줄 수 있는 가능성을 제시한다.
This study examined the effects of amygdala inactivation on the expression of conditioned fear and the performance of active avoidance. Rats, with chronic cannulae placed bilaterally in the amygdala, were given 30 active avoidance training trials for 3 days and 1 or 2 days later tested for conditioned fear and active avoidance immediately after muscimol or buffer injection into the amygdala. As a result, activity to the CS in the amygdala inactivation group was larger than that of controls while performance of active avoidance was not different. In other words, amygdala inactivation impaired expression of conditioned fear but not active avoidance response. These findings suggest that both memory storage and memory modulation, different view about the role of amygdala, are correct in part and the discrepancy between the two stems from the task difference in part. Thus, amygdala seems to be the locus of CS-US association and, at the same time, modulates memory consolidation in other brain regions. It means that neural mechanisms for the expression of conditioned fear and the performance of active avoidance are not the same.
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