Department of Brain and Cognitive Sciences, Seoul National University, Gwanak-gu, Seoul 151-742, Korea.
Learn Mem. 2011 Dec 14;19(1):1-8. doi: 10.1101/lm.024554.111. Print 2012 Jan.
Cued retrieval of memory is typically examined with delay when testing hippocampal functions, as in delayed matching-to-sample tasks. Equally emphasized in the literature, on the other hand, is the hippocampal involvement in making arbitrary associations. Paired associate memory tasks are widely used for examining this function. However, the two variables (i.e., delay and paired association) were often mixed in paired associate tasks, and this makes it difficult to localize the cognitive source of deficits with hippocampal perturbation. Specifically, a few studies have recently shown that rats can learn arbitrary paired associations between certain locations and nonspatial items (e.g., object or flavor) and later can retrieve the paired location when cued by the item remotely. Such tasks involve both (1) delay between sampling the cue and retrieving the target location and (2) arbitrary association between the cueing object and its paired location. Here, we tested whether delay was necessary in a cued paired associate task by using a task in which no delay existed between object cueing and the choice of its paired associate. Moreover, fixed associative relationships between the cueing objects and their paired locations were repeatedly used, thus involving no trial-unique association. Nevertheless, inactivations of the dorsal hippocampus with muscimol severely disrupted retrieval of paired associates, whereas the same manipulations did not affect discriminating individual objects or locations. The results powerfully demonstrate that the hippocampus is inherently required for retrieving paired associations between objects and places, and that delay and trial uniqueness of the paired associates are not necessarily required.
线索检索记忆通常在测试海马体功能时通过延迟来进行检验，例如在延迟匹配样本任务中。另一方面，文献中同样强调了海马体在形成任意联想中的作用。配对联想记忆任务被广泛用于检验这一功能。然而，在配对联想任务中，这两个变量（即延迟和配对联想）通常是混合的，这使得很难确定海马体干扰导致认知缺陷的来源。具体来说，最近的一些研究表明，大鼠可以学习特定地点和非空间项目（例如物体或味道）之间的任意配对联想，然后当被远程提示的项目 cue 时，可以检索配对的地点。这些任务涉及（1）在 cue 采样和检索目标位置之间的延迟，以及（2）cueing 对象与其配对位置之间的任意关联。在这里，我们通过使用一种不存在对象 cue 和其配对的选择之间的延迟的 cue 配对联想任务，来测试延迟在 cue 配对联想任务中的必要性。此外，我们反复使用 cueing 对象与其配对位置之间固定的关联关系，因此不涉及 trial-unique 关联。然而，用 muscimol 对背侧海马体进行失活处理严重破坏了对配对联想的检索，而相同的操作不会影响对单个物体或位置的辨别。这些结果有力地证明了海马体对于在物体和地点之间检索配对联想是必不可少的，并且延迟和配对联想的 trial-unique 并不是必需的。
