Neuroanatomical and neurophysiological basis of learning : plasticity of the insect brain

对四种昆虫的脑结构进行了研究：苍蝇的成虫和幼虫、美洲大蠊、工蜂和老虎甲虫的成虫和幼虫。复眼的视叶由三个神经毛组成：板层、髓质和小叶神经毛：板层和髓质神经毛是以视网膜视觉的方式组织的，而神经小叶的组织是为了整合这种视网膜视觉信息，以获得抽象的特定视觉信息。虎甲幼虫的视叶由两个神经纤维区组成：视网膜板层区和延髓整合区。视神经管的基本设计似乎是由遗传决定的，因为神经管的结构通常在幼虫和幼虫在持续的黑暗中分化。但是，在缺光条件下饲养的苍蝇视神经纤维结构发生了一些微小的变化：视网膜INT…的轴突更多的ER神经元减少。这些变化具有统计学意义，可能与神经束结构的可塑性有关。在这四个物种的大脑中，观察到了不同形式的感觉中间神经元的终末，包括视神经束的传入轴突和嗅叶的输出轴突。这些感觉中间神经元终止于前脑中的蘑菇体，表明那里有多模式的感觉整合。蘑菇体似乎也在自主行为的启动中起着主要作用，因为一些神经元在运动的启动之前就会发出信号。在喷气引发的蟑螂的运动、老虎甲虫幼虫的捕食和逃逸反应以及工蜂的视觉行为中，观察到了行为的戏剧性变化。这种变化必须植根于神经网络的可塑性变化，它包含了记忆和学习等高级神经功能的形态和生理基础。在本研究方案中，记录了蟑螂脑中与这种高级功能有关的神经活动。在蟑螂身上，被训练成学习一些视觉线索以避开不舒服的地方，发现了专门对这些视觉线索做出反应的神经元。这些结果可能是学习的生理对应，并暗示昆虫大脑的可塑性，以实现更高的神经功能。较少

Structure of the brain has been examined in four species of insects : adults and larvae of blowflies Phormia regina Meigen, adult cockroaches Periplaneta americana, worker honeybees Apis mellifera, and adults and larvae of tiger beetles Cicindela chinensis.The optic lobe of the compound eye consists of three neuropils : lamina, medulla and lobula neuropils : The lamina and medulla neuropils are organized retinotopically, whereas lobula neuropil is organized to integrate such retinotopic visual information for abstract specific visual information. The optic lobe of the tiger beetle larva consists of two neuropil regions : retinotopic lamina region and integrative medulla region. The basic design of optic neuropil appears to be genetically determined, because the neuropil structure is normally differentiated in the larval and pupal lifves under constant dark. But, some minute changes occurred in the fly optic neuropil structure reared under light-deprived condition : axons of retinal int … More erneurons decreased. Such changes were statistically significant, and may be related to plastic nature of the neuropil structure.Terminations of sensory interneurons of various modalities including afferent axons of the optic neuropil and output axons of olfactory lobe have been examined in the brain of the four species. Those sensory interneurons terminate in the mushroom body in the protocerebrum suggesting multimodal sensory integration there. The mushroom body also appears to play an primary role for initiation of voluntary behavior, because some neurons fire prior initiation of locomotion.Plastic changes of behavior were observed in locomotion of cockroaches triggered by air puffs, predatory and escape responses of tiger beetle larva and visual behavior of the worker honeybees. Such changes must be rooted in plastic changes of neural networks, which comprise morphological and physiological basis of higher neural function such as memory and learning. In this research program neural activities concerning to such higher function were recorded in cockroach brain. In the cockroach that was trained to learn some visual cue to avoid an uncomfortable place, the neurons exclusively responding to such visual cues were found.These results may be physiological counterpart of learning and are suggestive plastic nature of the insect brain for higher neural function. Less