Department of Psychology, Florida Atlantic University, Jupiter, Florida.
Center for Complex Systems and Brain Sciences, Florida Atlantic University, Boca Raton, Florida.
J Neurophysiol. 2020 Mar 1;123(3):1247-1264. doi: 10.1152/jn.00278.2019. Epub 2020 Feb 5.
Medial and lateral entorhinal cortices convey spatial/contextual and item/object information to the hippocampus, respectively. Whether the distinct inputs are integrated as one cognitive map by hippocampal neurons to represent location and the objects therein, or whether they remain as parallel outputs, to be integrated in a downstream region, remains unclear. Principal, or complex spike bursting, neurons of hippocampus exhibit location-specific firing, and it is likely that the activity of "place cells" supports spatial memory/navigation in rodents. Consistent with cognitive map theory, the activity of CA1 hippocampal neurons is also critical for nonspatial memory, such as object recognition. However, the degree to which CA1 neuronal activity represents the associations of object-context or object-in-place memory is not well understood. Here, the contributions of mouse CA1 neuronal activity to object recognition memory and the emergence of object-place conjunctive representations were tested using in vivo recordings and functional inactivation. Independent of arena configuration, CA1 place fields were stable throughout testing and object-place representations were not identified in CA1, although the number of fields per cell increased during object sessions, and few object-related firing CA1 neurons (nonplace) were recorded. The results of the inactivation studies confirmed the significant contribution of CA1 neuronal activity to object recognition memory when a delay of 20 min, but not 5 min, was imposed between encoding and retrieval. Together, our results confirm the delay-dependent contribution of the CA1 region to object memory and suggest that object information is processed in parallel with the ongoing spatial mapping function that is a hallmark of hippocampal memory. We developed variations of the object recognition task to examine the contribution of mouse CA1 neuronal activity to object memory and the degree to which object-context conjunctive representations are formed during object training. Our results indicate that, within the CA1 region, object information is processed in a parallel but delay-dependent manner, with ongoing spatial mapping.
内侧和外侧内嗅皮层分别将空间/上下文和项目/物体信息传递到海马体。海马体神经元是否将不同的输入整合为一个认知图，以表示位置和其中的物体，或者它们是否保持为平行输出，在下游区域进行整合，目前尚不清楚。海马体的主要或复杂尖峰爆发神经元表现出位置特异性放电，并且“位置细胞”的活动很可能支持啮齿动物的空间记忆/导航。与认知地图理论一致，CA1 海马体神经元的活动对于非空间记忆（例如物体识别）也是至关重要的。然而，CA1 神经元活动代表物体-上下文或物体-位置记忆关联的程度尚不清楚。在这里，使用体内记录和功能失活来测试小鼠 CA1 神经元活动对物体识别记忆和物体-位置联合表示的出现的贡献。独立于竞技场配置，CA1 位置场在整个测试过程中都是稳定的，并且在 CA1 中没有识别出物体-位置表示，尽管在物体会话期间每个细胞的场数增加了，并且记录到的与物体相关的放电 CA1 神经元（非位置）很少。失活研究的结果证实了 CA1 神经元活动对物体识别记忆的重要贡献，当在编码和检索之间施加 20 分钟而不是 5 分钟的延迟时。总的来说，我们的结果证实了 CA1 区域对物体记忆的延迟依赖性贡献，并表明物体信息与正在进行的空间映射功能平行处理，这是海马体记忆的标志。我们开发了物体识别任务的变体，以研究小鼠 CA1 神经元活动对物体记忆的贡献以及在物体训练过程中形成物体-上下文联合表示的程度。我们的结果表明，在 CA1 区域内，物体信息以平行但延迟依赖的方式与正在进行的空间映射一起处理。
