MICROCIRCUITRY OF PULVINAR AND NEOCORTICAL CONNECTIONS

枕和皮质之间的相互作用是功能性的， 数字重要。 然而，这个系统的组织水平 与其他主要的微电路相比， 皮质连接的中心，如基底神经节和特定的 丘脑感觉核 在这个项目中，我们将使用高分辨率 序列轴突重建和神经元分析，以测试和完善 一种普遍的假设， 不适用于丘脑联合核及其皮质 连通性。 初步结果表明， approach. 例如，我们现在有两种类型的证据 皮质柄终止：1）小，球形乔木，大珠状 结束，和2）延长终端，发散在几个 毫米，棘状末端特化（见附录：罗克兰， 1994年a）。 这些可能来自两个以前确定的种群， corticopulvinar神经元;即，第5层的巨型和中型金字塔。 我们 假设由具有宽树枝状场的金字塔采样的事件 “压缩”到枕中一个定界的终末病灶，而更多 局部化分析（由更多的中等金字塔执行）， 分布在枕神经元上 不同突触 机制也可能与大珠状vs. 棘突特化 提出了四个实验。 两个将使用PHA-L来识别 皮质枕和枕皮质轴突。 这些将被分析为 投影焦点，并在连续切片中重建，以确定这种 参数如轴突口径、分支、乔木大小和形状以及密度 的终止。 第三个实验将使用体内/体外组合 填充进行详细的绘图的两个人口 皮质丘脑投射神经元，在形态学和几何学方面 它们的树突状表型的特征。 我们将采用定量方法 为了确定巨大皮质髓神经元的密度， 与中皮质丘脑神经元的比例，以及区域特异性 差异 第四个实验涉及地形组织 和皮质-海绵体连接的会聚。 两个顺行示踪剂 将被注射到两个皮质的视觉上对应的病灶中 地区 这些数据可能会阐明从心理物理学， 生理和临床观察，因为这些涉及到的作用 选择性视觉注意中的枕。 划分两 锥体表型，以索马大小、树枝状乔木和 外源性轴突终末，可能与1）分离亚组分有关 注意力机制; 2）作为连接特定模型 支持进一步的分子和功能表征。 换句 系统，如膝状皮质，轴突微电路提供了一个 设计解释研究的有用基线， 塑性效应，拟议的研究计划可能会促进 类似的应用。

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.