Krieger Mind/Brain Institute, Johns Hopkins University Baltimore, MD, USA.
Front Comput Neurosci. 2011 Sep 29;5:39. doi: 10.3389/fncom.2011.00039. eCollection 2011.
Mammals navigate by integrating self-motion signals ("path integration") and occasionally fixing on familiar environmental landmarks. The rat hippocampus is a model system of spatial representation in which place cells are thought to integrate both sensory and spatial information from entorhinal cortex. The localized firing fields of hippocampal place cells and entorhinal grid-cells demonstrate a phase relationship with the local theta (6-10 Hz) rhythm that may be a temporal signature of path integration. However, encoding self-motion in the phase of theta oscillations requires high temporal precision and is susceptible to idiothetic noise, neuronal variability, and a changing environment. We present a model based on oscillatory interference theory, previously studied in the context of grid cells, in which transient temporal synchronization among a pool of path-integrating theta oscillators produces hippocampal-like place fields. We hypothesize that a spatiotemporally extended sensory interaction with external cues modulates feedback to the theta oscillators. We implement a form of this cue-driven feedback and show that it can retrieve fixed points in the phase code of position. A single cue can smoothly reset oscillator phases to correct for both systematic errors and continuous noise in path integration. Further, simulations in which local and global cues are rotated against each other reveal a phase-code mechanism in which conflicting cue arrangements can reproduce experimentally observed distributions of "partial remapping" responses. This abstract model demonstrates that phase-code feedback can provide stability to the temporal coding of position during navigation and may contribute to the context-dependence of hippocampal spatial representations. While the anatomical substrates of these processes have not been fully characterized, our findings suggest several signatures that can be evaluated in future experiments.
哺乳动物通过整合自身运动信号（“路径整合”）并偶尔固定在熟悉的环境地标上来进行导航。大鼠海马体是空间表示的模型系统，其中位置细胞被认为整合了来自内嗅皮层的感觉和空间信息。海马体位置细胞和内嗅网格细胞的局部放电场与局部 theta（6-10 Hz）节律表现出相位关系，这可能是路径整合的时间特征。然而，在 theta 振荡的相位中编码自身运动需要高时间精度，并且容易受到内感受噪声、神经元变异性和不断变化的环境的影响。我们提出了一个基于振荡干扰理论的模型，该理论以前在网格细胞的背景下进行过研究，其中一组路径整合 theta 振荡器之间的短暂时间同步产生类似于海马体的位置场。我们假设与外部线索的时空扩展感觉相互作用会调节对 theta 振荡器的反馈。我们实现了这种线索驱动反馈的一种形式，并表明它可以检索位置相位代码中的固定点。单个线索可以平滑地重置振荡器相位，以纠正路径整合中的系统误差和连续噪声。此外，在局部和全局线索相互旋转的模拟中，揭示了一种相位码机制，其中冲突的线索安排可以再现实验观察到的“部分重映射”反应的分布。这个抽象模型表明，相位码反馈可以在导航过程中为位置的时间编码提供稳定性，并可能有助于海马体空间表示的上下文依赖性。虽然这些过程的解剖学基础尚未完全描述，但我们的发现提出了一些可以在未来实验中评估的特征。
