Department of Brain and Cognitive Sciences, Seoul National University, Gwanak-gu, Seoul, Korea 08826.
Department of Brain and Cognitive Sciences, Seoul National University, Gwanak-gu, Seoul, Korea 08826
J Neurosci. 2018 Aug 22;38(34):7392-7408. doi: 10.1523/JNEUROSCI.0156-18.2018. Epub 2018 Jul 16.
Literature suggests that the hippocampus is central to processing visual scenes to remember contextual information, but the roles of its downstream structure, subiculum, remain unknown. Here, single units were recorded simultaneously in the dorsal CA1 and subiculum while male rats made spatial choices using visual scenes as cues in a T-maze. The firing fields of subicular neurons were schematically organized following the task structure, largely divided into pre-choice and post-choice epochs, whereas those of CA1 cells were more punctate and bound to specific locations. When the rats were tested with highly familiar scenes, neurons in the CA1 and subiculum were indistinguishable in coding the task-related information (e.g., scene, choice) through rate remapping. However, when the familiar scenes were blurred parametrically, the neurons in the CA1 responded sensitively to the novelty in task demand and changed its representations parametrically following the physical changes of the stimuli, whereas these functional characteristics were absent in the subiculum. These results suggest that the unique function of the hippocampus is to acquire contextual representations in association with discrete positions in space, especially when facing new and ambiguous scenes, whereas the subiculum may translate the position-bound visual contextual information of the hippocampus into schematic codes once learning is established. Although the potential functional significance has been recognized for decades for the subiculum, its exact roles in a goal-directed memory task still remain elusive. In the current study, we present experimental evidence that may indicate that the neural population in the subiculum could translate the location-bound spatial representations of the hippocampus into more schematic representations of task demands. Our findings also imply that the visual scene-based codes conveyed by the hippocampus and subiculum may be identical in a well learned task, whereas the hippocampus may be more specialized in representing altered visual scenes than the subiculum.
文献表明，海马体在处理视觉场景以记忆上下文信息方面起着核心作用，但它的下游结构——下托的作用仍然未知。在这里，当雄性大鼠在 T 型迷宫中使用视觉场景作为线索进行空间选择时，我们同时在背侧 CA1 和下托中记录了单个神经元的活动。下托神经元的发放场域按照任务结构进行了示意性组织，主要分为选择前和选择后两个时期，而 CA1 细胞的发放场域则更加分散且与特定位置相关。当用高度熟悉的场景测试大鼠时，CA1 和下托中的神经元在通过重新映射率对与任务相关的信息（例如场景、选择）进行编码方面无法区分。然而，当熟悉的场景参数模糊化时，CA1 中的神经元对任务需求中的新颖性非常敏感，并且会根据刺激的物理变化参数化地改变其表示，而这些功能特征在下托中不存在。这些结果表明，海马体的独特功能是与空间中的离散位置相关联地获取上下文表示，尤其是在面对新的和模糊的场景时，而下托可能会将海马体的位置绑定的视觉上下文信息转化为示意性编码，一旦学习建立。尽管几十年来人们已经认识到下托的潜在功能意义，但它在目标导向记忆任务中的确切作用仍然难以捉摸。在本研究中，我们提出了实验证据，表明下托中的神经群体可能将海马体的位置绑定的空间表示转化为更示意性的任务需求表示。我们的发现还表明，在一个学习良好的任务中，由海马体和下托传递的基于视觉场景的代码可能是相同的，而海马体可能比下托更专门地表示改变后的视觉场景。
