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

研究了四种昆虫的脑结构：丽蝇（Phormia regina Meigen）的成虫和幼虫、美洲大蠊（Periplaneta americana）的成虫、蜜蜂（Apis mellifera）的工蜂、虎甲虫（Cicinaciensis）的成虫和幼虫。板层和髓质神经髓鞘是视网膜定位的，而小叶神经髓鞘是为了整合这些视网膜定位的视觉信息而组织的，以获得抽象的特定视觉信息。虎甲虫幼虫的视叶由两个神经毡区组成：视网膜定位板区和整合髓质区。视神经鞘的基本设计似乎是由遗传决定的，因为视神经鞘的结构通常在幼虫和蛹的生活中在恒定的黑暗下分化。但是，在光剥夺条件下饲养的果蝇视神经元结构发生了一些微小的变化：视网膜神经元的轴突， ...更多信息 神经元减少。这些变化在统计学上是显著的，可能与神经元结构的可塑性有关。在四种动物的脑中，观察了各种感觉中间神经元的终末，包括视神经元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的蘑菇体，表明那里存在多模式感觉整合。蘑菇体也似乎在自发行为的启动中起主要作用，因为一些神经元在自发行为的启动之前就被激活了。在由空气喷气触发的蟑螂的运动、虎甲虫幼虫的捕食和逃跑反应以及工蜂的视觉行为中观察到了行为的可塑性变化。这种变化必须植根于神经网络的可塑性变化，神经网络包括高级神经功能（如记忆和学习）的形态和生理基础。本研究记录了蟑螂脑中与这种高级功能有关的神经活动。在被训练学习某些视觉线索以避开不舒服的地方的蟑螂中，发现了专门响应这种视觉线索的神经元。这些结果可能是学习的生理对应物，并且暗示昆虫大脑具有高级神经功能的可塑性。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