Tanila H, Shapiro M L, Eichenbaum H
Department of Neuroscience and Neurology, University of Kuopio, Finland.
Hippocampus. 1997;7(6):613-23. doi: 10.1002/(SICI)1098-1063(1997)7:6<613::AID-HIPO4>3.0.CO;2-F.
The extent to which small ensembles of neighboring hippocampal neurons alter their spatial firing patterns concurrently in response to stimulus manipulations was examined in young adult rats as well as in aged rats with and without memory impairment. Recordings from CA1 and CA3 cells were taken as rats performed a spatial radial-maze task that employed prominent distal visual stimuli attached to dark curtains surrounding the maze and local cues on each maze arm provided by inserts with distinctive visual, tactile, and olfactory stimuli. To test the influence of the different stimulus subsets, the distal and local cues were rotated 90 degrees in opposite directions (a Double Rotation). In response to this manipulation, place fields could maintain a fixed position to room coordinates, rotate with either the local or the distal cues, disappear, or new fields could appear. On average 79% of the cells within an ensemble responded in the same way, but only 37% of all ensembles were fully concordant. Typically discordant ensembles had place fields that rotated with one set of cues, whereas the other fields disappeared or new fields appeared. Ensembles in which the place fields rotated in two opposite directions were less frequent in young rats than would be expected by the occurrence of the individual responses, indicating selective competition between directly conflicting representations and ultimate suppression of one. These findings indicate that hippocampal neurons independently encode distinct subsets of the cues in a complex environment, although processing within the hippocampal network may actively reduce the simultaneous representation of conflicting orientation information. This kind of population activity might reflect the higher-order organization of new memories within an established knowledge framework or schema. Concordance was higher in aged memory-impaired rats than in young rats, and the suppression of conflicting representations was absent in these rats. These findings suggest that age-related memory impairment is at least in part associated with a decrease in the scope of information coded and in the coordination of encoded representations.
在年轻成年大鼠以及有和没有记忆损伤的老年大鼠中，研究了相邻海马神经元的小集合在响应刺激操作时同时改变其空间放电模式的程度。当大鼠执行空间放射状迷宫任务时，对CA1和CA3细胞进行记录，该任务采用附着在迷宫周围深色窗帘上的突出远端视觉刺激以及由具有独特视觉、触觉和嗅觉刺激的插入物在每个迷宫臂上提供的局部线索。为了测试不同刺激子集的影响，将远端和局部线索以相反方向旋转90度（双旋转）。响应这种操作，位置场可以保持相对于房间坐标的固定位置，随局部或远端线索旋转，消失，或者可以出现新的场。平均而言，一个集合中的79%的细胞以相同方式做出反应，但所有集合中只有37%完全一致。典型的不一致集合具有随一组线索旋转的位置场，而其他场消失或出现新的场。在年轻大鼠中，位置场沿两个相反方向旋转的集合比个体反应发生时预期的要少，这表明直接冲突表征之间存在选择性竞争，最终一个被抑制。这些发现表明，海马神经元在复杂环境中独立编码线索的不同子集，尽管海马网络内的处理可能会积极减少冲突方向信息的同时表征。这种群体活动可能反映了既定知识框架或图式内新记忆的高阶组织。老年记忆受损大鼠的一致性高于年轻大鼠，并且这些大鼠中不存在对冲突表征的抑制。这些发现表明，与年龄相关的记忆损伤至少部分与编码信息范围的减少以及编码表征的协调有关。
