School of Psychology, Cardiff University, United Kingdom.
Hippocampus. 2011 Sep;21(9):945-57. doi: 10.1002/hipo.20796. Epub 2010 May 7.
It is now clear that the integrity of the fornix is important for normal mnemonic function. The fornix, however, is a major white matter tract, carrying numerous hippocampal formation afferents and efferents, and it is not known which specific components support memory processes. Established theories of extended hippocampal function emphasize the sequential pathway from the hippocampal formation (i.e., subicular complex) to the mammillary bodies and, thence, to the anterior thalamus, as pathology in each of these structures is implicated in anterograde amnesia in humans and spatial memory deficits in rats. The specific importance of the hippocampal formation projections that just innervate the mammillary bodies has, however, never been tested. This study isolated these specific projections in the rat by selectively cutting the descending component of the postcommissural fornix. Two successive, cohorts of rats with these tract lesions were tested on working memory tasks in the water-maze, T-maze, and radial-arm maze. Disconnecting the descending postcommissural fornix had only a mild effect or sometimes no apparent effect on the performance of these spatial memory tasks, even though tracing experiments confirmed the loss of hippocampal formation-mammillary projections. One implication is that the spatial deficits found in rats following standard fornix lesions are only partly attributable to the loss of projections from the hippocampal formation to the mammillary bodies. Perhaps more surprising, the behavioral impact of cutting the descending postcommissural fornix in rats appeared appreciably less than the effect of either mammillary body or mammillothalamic tract lesions. The present experiments show that the mammillary bodies can still effectively support spatial memory in the absence of their dense subicular complex inputs, so revealing the importance of the other afferents for sustaining mammillary body function. This new evidence for independent functions shows that the mammillary bodies are more than just a hippocampal relay.
现在很清楚，穹窿的完整性对于正常的记忆功能很重要。然而，穹窿是一个主要的白质束，携带许多海马结构的传入和传出纤维，目前还不知道哪些特定的成分支持记忆过程。扩展的海马功能的既定理论强调了从海马结构（即，下托复合体）到乳头体，然后到前丘脑的顺序途径，因为这些结构中的每一个结构的病理学都与人类的顺行性遗忘和大鼠的空间记忆缺陷有关。然而，刚刚支配乳头体的海马结构投射的具体重要性从未得到过检验。这项研究通过选择性地切割穹窿后连合的下降成分，在大鼠中分离出这些特定的投射。用这些束损伤的大鼠进行了两批连续的工作记忆任务测试，测试方法包括水迷宫、T 迷宫和放射臂迷宫。即使追踪实验证实了海马结构-乳头体投射的丧失，切断穹窿后连合的下降部分对这些空间记忆任务的表现只有轻微的影响，或者有时没有明显的影响。一种推论是，标准穹窿损伤后大鼠中发现的空间缺陷仅部分归因于海马结构到乳头体的投射丧失。也许更令人惊讶的是，在大鼠中切断穹窿后连合的下降部分的行为影响明显小于切除乳头体或乳头丘脑束的影响。本实验表明，在没有密集的下托复合体输入的情况下，乳头体仍然可以有效地支持空间记忆，从而揭示了其他传入纤维对维持乳头体功能的重要性。这种独立功能的新证据表明，乳头体不仅仅是海马的中继。
