Shapiro M L, Tanila H, Eichenbaum H
Department of Psychology, McGill University, Montreal, Canada.
Hippocampus. 1997;7(6):624-42. doi: 10.1002/(SICI)1098-1063(1997)7:6<624::AID-HIPO5>3.0.CO;2-E.
Hippocampal place fields were recorded as rats explored a four-arm radial maze surrounded by curtains holding distal stimuli and with distinct local tactile, olfactory, and visual cues covering each arm. Systematic manipulations of the individual cues and their interrelationships showed that different hippocampal neurons encoded individual local and distal cues, relationships among cues within a stimulus set, and the relationship between the local and distal cues. Double rotation trials, which maintained stimulus relationships within distal and local cue sets, but altered the relationship between them, often changed the responses of the sampled neural population and produced new representations. After repeated double rotation trials, the incidence of new representations increased, and the likelihood of a simple rotation with one of the cue sets diminished. Cue scrambling trials, which altered the topological relationship within the local or distal stimulus set, showed that the cells that followed one set of controlled stimuli responded as often to a single cue as to the constellation. These cells followed the single cue when the stimulus constellation was scrambled, but often continued firing in the same place when the stimulus was removed or switched to respond to other cues. When the maze was surrounded by a new stimulus configuration, all of the cells either developed new place fields or stopped firing, showing that the controlled stimuli had persistent and profound influence over hippocampal neurons. Together, the results show that hippocampal neurons encode a hierarchical representation of environmental information.
当大鼠探索一个四臂放射状迷宫时，记录海马位置场。该迷宫被带有远端刺激的帘子包围，每个臂上覆盖有独特的局部触觉、嗅觉和视觉线索。对单个线索及其相互关系进行系统操纵表明，不同的海马神经元编码单个局部和远端线索、刺激集内线索之间的关系以及局部和远端线索之间的关系。双旋转试验保持了远端和局部线索集内的刺激关系，但改变了它们之间的关系，常常会改变采样神经群体的反应并产生新的表征。经过反复的双旋转试验后，新表征的发生率增加，而线索集之一进行简单旋转的可能性降低。线索扰乱试验改变了局部或远端刺激集内的拓扑关系，结果表明，跟随一组受控刺激的细胞对单个线索的反应与对整个刺激群的反应一样频繁。当刺激群被扰乱时，这些细胞跟随单个线索，但当刺激被移除或切换以响应其他线索时，它们通常仍在同一位置持续放电。当迷宫被新的刺激配置包围时，所有细胞要么形成新的位置场，要么停止放电，这表明受控刺激对海马神经元具有持久而深远的影响。总之，这些结果表明海马神经元编码环境信息的层次表征。
