Neural Organization of the Protocerebrum of an Insect

本研究的目的是阐明昆虫前脑的基本神经组织，其中来自各种感觉系统的信号被整合并转换为运动动作的命令信号。这些信号通过许多下行神经元（DN）传递到胸部运动中枢。本研究首先从颈结缔组织逆行填充美洲大蠊（Periplaneta americana）脑内的神经元轴突，观察其胞体和树突的分布。结果显示，在235对DNs胞体中，大部分位于前脑。树突状分支的DNs被发现在各种各样的神经元区域，但不是在视叶，触角叶，蘑菇体，中央复合体，和腹侧的一部分的侧角。上行神经元的轴突终末也广泛分布于不同脑区。基于这些发现，我们提出，有一些平行的处理流从头部的感觉区到胸部运动中心，其中许多是通过不同的运动前区的大脑，也从更高的联合区的通路供应一些运动前区，形成分层的处理流。通过研究蟑螂大脑中记录的发现，我们提出，并行处理流在各种反射和本能行为中发挥作用，而分层处理流则控制着某些形式的经验依赖性行为修改。接下来，我检查了蟑螂外侧前脑的神经组织，发现这是一个高度组织化的神经系统，由许多功能细分组成。

The aim of this study was to clarify basic neural organization of the protocerebrum of insects, where signals from various sensory systems are integrated and are converted into command signals for motor actions. Such signals are transmitted to thoracic locomotory centers via a number of descending neurons (DNs). At first, I examined the distribution of somata and dendrites of DNs of tne brain of the cockroach Periplaneta americana, by retrogradely filling their axons from the cervical connective. About 235 pairs of somata of DNs were stained, a majority of which is located in the protocerebrum. Dendritic arborizations of DNs are found in wide varieties of neuropil areas but not in the optic lobe, the antennal lobe, the mushroom body, the central complex, and ventral part of the lateral horn. Axon terminals of ascending neurons were also found in wide varieties of brain areas. Based on these findings, we propose that there is a number of parallel processing streams from cephalic sensory areas to thoracic locomotory centers, many of which are via various premotor areas of the brain, and also that pathways from higher association areas supply some premotor areas to form hierarchical processing streams. By examining documented findings in the cockroach brain, we propose that parallel processing streams function in various reflexive and instinctive behaviors, while hierarchical processing steams govern some forms of experience-dependent modification of behavior. Next, I examined neural organizations of the lateral protocerebrum of the cockroach, and found that this is a highly organized neuropil consisting of a number of functional subdivisions.