Takahashi Muneyoshi, Lauwereyns Johan, Sakurai Yoshio, Tsukada Minoru
Tamagawa University Brain Science Institute, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan.
J Neurophysiol. 2009 Jul;102(1):556-67. doi: 10.1152/jn.91159.2008. Epub 2009 May 6.
The classical notion of hippocampal CA1 "place cells," whose activity tracks physical locations, has undergone substantial revision in recent years. Here, we provide further evidence of an abstract spatial code in hippocampal CA1, which relies on memory and adds complexity to the basic "place cell." Using a nose-poking paradigm with four male Wistar rats, we specifically concentrated on activity during fixation, when the rat was immobile and waiting for the next task event in a memory-guided spatial alternation task. The rat had to alternate between choosing the right and left holes on a trial-by-trial basis, without any sensory cue, and relying on an internal representation of the sequence of trials. Twelve tetrodes were chronically implanted for single-unit recording in the right CA1 of each rat. We focus on 76 single neurons that showed significant activation during the fixation period compared with baseline activity between trials. Among these 76 fixation neurons, we observed 38 neurons that systematically changed their fixation activity as a function of the alternation sequence. That is, even though these rats were immobile during the fixation period, the neurons fired differently for trials in which the next spatial choice should be left (i.e., RIGHT-TO-LEFT trials) compared with trials in which the next spatial choice should be right (i.e., LEFT-TO-RIGHT trials), or vice versa. Our results imply that these neurons maintain a sequential code of the required spatial response during the alternation task and thus provide abstract information, derived from memory, that can be used for efficient navigation.
海马体CA1区“位置细胞”的经典概念认为，其活动追踪物理位置，但近年来这一概念已发生了重大修正。在此，我们提供了海马体CA1区存在抽象空间编码的进一步证据，该编码依赖于记忆，并为基本的“位置细胞”增添了复杂性。我们使用四头雄性Wistar大鼠进行戳鼻范式实验，特别关注了在记忆引导的空间交替任务中大鼠静止不动并等待下一个任务事件时的注视期间的活动。大鼠必须在每次试验中在左右两个洞之间交替选择，没有任何感官提示，而是依靠对试验序列的内部表征。每只大鼠的右侧CA1区长期植入了12根四极管用于单神经元记录。我们关注的是76个单神经元，与试验间的基线活动相比，它们在注视期间表现出显著激活。在这76个注视神经元中，我们观察到38个神经元的注视活动会根据交替序列系统地发生变化。也就是说，即使这些大鼠在注视期间静止不动，但对于下一个空间选择应为左侧的试验（即从右到左试验），与下一个空间选择应为右侧的试验（即从左到右试验）相比，这些神经元的放电情况不同，反之亦然。我们的结果表明，这些神经元在交替任务期间维持了所需空间反应的序列编码，从而提供了源自记忆的抽象信息，可用于高效导航。
