MICROCIRCUITRY OF PULVINAR AND NEOCORTICAL CONNECTIONS

枕骨和皮质之间的相互作用在功能上和 在数字上很重要。然而，这一系统在一级的组织 与其他专业相比，人们对微电路的了解很少 皮质连接的中枢，如基底节和特定的 丘脑感觉核团。在这个项目中，我们将使用高分辨率 连续轴突重建和神经元分析以测试和提炼 从特定感官通路派生出的原理的一般假设 不适用于联合丘脑核团及其皮质 连通性。初步结果说明了这一点的前景。 接近。例如，我们现在有两种类型的证据 皮质杨树顶端：1)带大珠子的小的球形乔木 末端，和2)细长的末端，分成几个 毫米，具有棘状终端专门化(见附录：Rockland， 1994a)。它们可能起源于先前发现的两个种群 即第5层的大锥体和中锥体。 假设由具有宽树突域的金字塔采样的事件是 “压缩”到枕骨的一个有分界的终端焦点，而更多 局部化分析(由更多的中等金字塔执行)是 分布在枕部神经元的集合上。不同的突触 机制也可能与大型串珠与 尖酸刻薄的专业。 提出了四个实验。两人将使用PHA-L来识别 大脑皮层和枕叶皮质轴突。这些内容将被分析为 投影焦点，并在连续切片中重建以确定 轴突直径、分支、茎的大小和形状以及密度等参数 终结者。第三个实验将使用体内/体外联合实验 填充以对这两个种群进行详细测绘 大脑白质投射神经元的形态计量学和几何学研究 它们的树突状表型特征。我们将采用定量的方法 为了确定巨大的皮质杨树神经元的密度，他们的 与中等皮质杨树神经元的比例，以及特定区域 不同之处。第四个实验针对地形组织 和皮质-白质连接的汇聚。两个顺行示踪器 将被注射到视觉上相对应的两个皮质 区域。 这些数据可能会阐明由心理物理引起的问题， 生理和临床观察，因为这些与 在选择性视觉注意中的枕骨。两个人的身份识别 锥体表型，以胞体大小、树枝和 外源性轴突终末可能与1)分离的亚组分有关 2)作为一种特定于连接的模型 支持进一步的分子和功能表征。在其他 膝状体皮质、轴突微电路等系统提供了一种 在解释与以下研究相关的研究时设计有用的基准 塑性效应，以及拟议的研究计划可能会促进 类似的应用程序。

Interactions between the pulvinar and cortex are functionally and numerically important. Yet, the organization of this system at the level of microcircuitry is poorly understood by comparison with other major cortically-linked centers, such as the basal ganglia and the specific sensory thalamic nuclei. In this project, we will use high resolution serial axon reconstruction and neuron analysis to test and refine the general hypothesis that principles derived from specific sensory pathways do not apply to associational thalamic nuclei and to their cortical connectivity. Preliminary results illustrate the promise of this approach. For example, we now have evidence for two types of corticopulvinar terminations: 1) small, spherical arbors with large beaded endings, and 2) elongated terminations, diverging over several millimeters, with spinous terminal specializations (see Appendix:Rockland, 1994a). These may originate from two previously identified populations of corticopulvinar neurons; namely, giant and medium pyramids of layer 5. We hypothesize that events sampled by pyramids with wide dendritic fields are "compressed" to a delimited terminal focus in the pulvinar, whereas more localized analysis (performed by the more numerous medium pyramids) is distributed over an assembly of pulvinar neurons. Different synaptic mechanisms are also likely to be associated with the large beaded vs. spinous specializations. Four experiments are proposed. Two will use PHA-L to identify corticopulvinar and pulvinocortical axons. These will be analyzed as projection foci, and reconstructed in serial sections to determine such parameters as axon caliber, branching, arbor size and shape, and density of terminations. A third experiment will use combined in vivo/in vitro filling to carry out a detailed mapping of the two populations of corticopulvinar projection neurons, in terms of morphometric and geometric features of their dendritic phenotype. We will apply quantitative methods to determine the density of giant corticopulvinar neurons, their proportion to medium corticopulvinar neurons, and area-specific differences. A fourth experiment addresses the topographic organization and convergence of corticopulvinar connections. Two anterograde tracers will be injected into visuotopically corresponding foci of two cortical areas. These data may illuminate questions arising from psychophysical, physiological and clinical observations, as these relate to the role of the pulvinar in selective visual attention. The identification of two pyramidal phenotypes, distinguished by soma size, dendritic arbor, and extrinsic axon terminations, may be relevant 1) to separate subcomponents of attention mechanisms; and 2) as a connectionally-specific model supporting further molecular and functional characterization. In other systems such as the geniculocortical, axon microcircuitry has provided a useful baseline for design in interpretation of studies related to plasticity effects, and the proposed program of research may promote similar applications.