Gaskin Stephane, White Norman M
Department of Psychology, McGill University, Montreal, Quebec, Canada.
Hippocampus. 2007;17(7):586-94. doi: 10.1002/hipo.20295.
The relationship of the entorhinal cortex (EC) and fimbria-fornix (FF) in unreinforced spatial (latent) learning was studied using the conditioned-cue-preference task on an eight-arm radial maze. The maze was turned before every trial to eliminate the use of local cues. During three pre-exposure sessions, food-deprived rats explored the center platform and two adjacent arms of the maze. Since most of the same cues were visible from both arm locations, discriminating them required spatial learning. The rats were then alternately confined to the end of each arm over several days: one arm always contained food, the other was empty. Finally, the rats were allowed free access to both arms with no food present. Normal rats spent more time in their food-paired than in their unpaired arms showing that they learned to discriminate between the arm locations. Bilateral micro-injections of muscimol into the dorsal, but not into the ventral EC, given before the pre-exposure sessions only, impaired the discrimination. The discrimination was also impaired in rats with unilateral lesions of FF and contralateral injections of muscimol into the dorsal EC given before the pre-exposure sessions. Ipsilateral FF lesions and entorhinal inactivation had no effect. These results indicate that the acquisition of information during unreinforced exploration of a novel environment requires an intact circuit involving the dorsal EC and fimbria fornix. Together with previous reports, that this form of learning does not require a functional hippocampus, (Gaskin et al. (2005) Hippocampus 15:1085-1093) the findings also suggest that the acquisition of certain kinds of unreinforced information by this circuit is independent of the hippocampus.
利用八臂放射状迷宫上的条件线索偏好任务，研究了内嗅皮质（EC）和穹窿海马伞（FF）在非强化空间（潜在）学习中的关系。每次试验前转动迷宫以消除局部线索的使用。在三个预暴露阶段，饥饿的大鼠探索迷宫的中央平台和两个相邻的臂。由于从两个臂的位置都能看到大部分相同的线索，区分它们需要空间学习。然后，在几天内将大鼠交替限制在每个臂的末端：一个臂总是有食物，另一个是空的。最后，让大鼠在没有食物的情况下自由进入两个臂。正常大鼠在与食物配对的臂上花费的时间比在未配对的臂上多，这表明它们学会了区分臂的位置。仅在预暴露阶段之前，双侧向背侧而非腹侧EC微量注射蝇蕈醇会损害这种区分能力。在FF单侧损伤且在预暴露阶段之前向背侧EC对侧注射蝇蕈醇的大鼠中，这种区分能力也受到损害。同侧FF损伤和内嗅皮质失活没有影响。这些结果表明，在对新环境的非强化探索过程中获取信息需要一个完整的回路，该回路涉及背侧EC和穹窿海马伞。与之前的报告一致，即这种学习形式不需要功能性海马体（Gaskin等人，（2005年）《海马体》15:1085 - 1093），这些发现还表明，该回路获取某些类型的非强化信息独立于海马体。
