Department of Psychology, Philipps-University of Marburg, Germany.
Hippocampus. 2012 May;22(5):1202-14. doi: 10.1002/hipo.20965. Epub 2011 Jul 11.
It is commonly accepted that the hippocampus plays a major role in declarative memory across species and that it is of particular relevance for spatial memory in rodents. However, the interplay between hippocampal function and nondeclarative memory systems, such as procedural stimulus-response (S-R) or sequential learning, is less clear: depending on task requirements, an interaction, dissociation or interference between hippocampal function and other memory systems may occur. This study was conducted to investigate the influence of dorsal ibotenic hippocampal lesions on learning and performance of sequential behavior in a rat version of the serial reaction time task (SRTT). Magnetic resonance imaging (MRI) analyses of the lesions revealed a bilateral volume reduction of ≈ 46% (histological analyses: ≈ 59%) of the total hippocampus. They were largely confined to its dorsal part and led to an expected spatial memory deficits in an object place recognition test as compared to healthy controls, even though sham lesions had the same effect. Our earlier studies on sequential learning had revealed substantial impairments in case of dorsal striatal dopaminergic lesions. In the present study, however, hippocampal lesioned animals unexpectedly showed superior performance throughout SRTT testing and training as compared to controls, which resulted in a higher degree of subsequent automated sequential behavior. Thus, our data reveal the infrequent case where hippocampal lesions lead to long-term improvements in test performance of a type of rather complex procedural behavior. One possible explanation for this effect is that hippocampal activity in rodents can interfere with other memory systems during the acquisition of procedural tasks with very low spatial requirements, as used here. Alternative explanations for the observed superior SRTT performance in lesioned animals, such as hyperactivity or increased exploratory drive are also topic of the discussion.
人们普遍认为，海马体在物种间的陈述性记忆中起着主要作用，并且对啮齿动物的空间记忆尤其重要。然而，海马体功能与非陈述性记忆系统（例如程序性刺激-反应[S-R]或序列学习）之间的相互作用尚不清楚：根据任务要求，海马体功能与其他记忆系统之间可能会发生相互作用、分离或干扰。本研究旨在调查背侧损毁对大鼠序列反应时任务（SRTT）中序列行为学习和表现的影响。对损伤的磁共振成像（MRI）分析显示，总海马体的体积减少了约 46%（组织学分析：约 59%）。它们主要局限于背侧部分，并导致与健康对照组相比，在物体位置识别测试中出现预期的空间记忆缺陷，即使假损伤也有相同的效果。我们之前关于序列学习的研究表明，背侧纹状体多巴胺能损伤会导致明显的损伤。然而，在本研究中，与对照组相比，海马体损伤动物在 SRTT 测试和训练中出人意料地表现出更好的性能，这导致随后的自动序列行为程度更高。因此，我们的数据揭示了一个罕见的情况，即海马体损伤会导致一种相对复杂的程序性行为的测试表现长期改善。这种效应的一个可能解释是，在使用这里的低空间要求的程序性任务的获取过程中，啮齿动物的海马体活动可能会干扰其他记忆系统。对于损伤动物在 SRTT 中表现出更好的表现的观察结果，例如过度活跃或增加的探索驱动力，也有其他解释。
