Giocomo Lisa M, Hasselmo Michael E
Center for Memory and Brain, Program in Neuroscience, and Psychology Department, Boston University, Boston, Massachusetts 02215, USA.
Hippocampus. 2008;18(12):1186-99. doi: 10.1002/hipo.20501.
Recordings in awake, behaving animals demonstrate that cells in medial entorhinal cortex (mEC) show "grid cell" firing activity when a rat explores an open environment. Intracellular recording in slices from different positions along the dorsal to ventral axis show differences in intrinsic properties such as subthreshold membrane potential oscillations (MPO), resonant frequency, and the presence of the hyperpolarization-activated cation current (h-current). The differences in intrinsic properties correlate with differences in grid cell spatial scale along the dorsal-ventral axis of mEC. Two sets of computational models have been proposed to explain the grid cell firing phenomena: oscillatory interference models and attractor-dynamic models. Both types of computational models are briefly reviewed, and cellular experimental evidence is interpreted and presented in the context of both models. The oscillatory interference model has variations that include an additive model and a multiplicative model. Experimental data on the voltage-dependence of oscillations presented here support the additive model. The additive model also simulates data from ventral neurons showing large spacing between grid firing fields within the limits of observed MPO frequencies. The interactions of h-current with synaptic modification suggest that the difference in intrinsic properties could also contribute to differences in grid cell properties due to attractor dynamics along the dorsal to ventral axis of mEC. Mechanisms of oscillatory interference and attractor dynamics may make complementary contributions to the properties of grid cell firing in entorhinal cortex.
对清醒状态下活动的动物进行的记录表明，当大鼠探索开放环境时，内嗅皮质内侧（mEC）中的细胞会表现出“网格细胞”放电活动。对沿背腹轴不同位置切片进行的细胞内记录显示，其内在特性存在差异，如阈下膜电位振荡（MPO）、共振频率以及超极化激活阳离子电流（h电流）的存在情况。内在特性的差异与mEC背腹轴上网格细胞空间尺度的差异相关。已经提出了两组计算模型来解释网格细胞放电现象：振荡干扰模型和吸引子动力学模型。本文简要回顾了这两种类型的计算模型，并在两种模型的背景下解释和呈现了细胞实验证据。振荡干扰模型有多种变体，包括加法模型和乘法模型。此处给出的关于振荡电压依赖性的实验数据支持加法模型。加法模型还模拟了来自腹侧神经元的数据，这些数据显示在观察到的MPO频率范围内，网格放电场之间的间距很大。h电流与突触修饰的相互作用表明，由于mEC背腹轴上的吸引子动力学，内在特性的差异也可能导致网格细胞特性的差异。振荡干扰和吸引子动力学机制可能对内嗅皮质中网格细胞放电的特性做出互补贡献。
