Enzymes and Amines.  An enzyme is a substance that is capable of causing chemical change in another substance without undergoing any change itself. Enzymes play an important role in all the biochemical activities of the body. One of their major functions is to aid in the metabolism of amines, molecules derived from amino acids. Amine metabolism goes on in all tissues, including the brain, and it has been theorized that an accumulation of amines in the brain may be a causative factor in mental illness. It is known that the drug amphetamine, which contains amine molecules, inhibits cellular respiration in cerebral tissue and acts as a stimulant.

酶和胺。酶是一种能够引起另一种物质发生化学变化，自身却不变化的物质。酶在身体的所有生物化学活动中起着重要作用。它们的主要功能之一是帮助来源于氨基酸分子，胺的新陈代谢。在所有组织中，包括脑在内，都有持续胺的新陈代谢，从理论上说，脑中胺的积累可能是精神疾病的一个成因。众所周知，含有胺分子的苯丙胺药物，能抑制大脑组织中细胞的呼吸，并作为一种兴奋剂。

The activity of monoamine oxidase, one of the most active enzymes contributing to the oxidation of amines, has aroused much interest in the fields of neurochemistry and psychiatry. One of the first really effective antidepressants, iproniazid, was found to inhibit the action of monoamine oxidase, apparently bringing about an increase of cerebral amines and producing a stimulating action that relieves the patient’s depression. This discovery has led to a search for other monoamine oxidase inhibitors.

单胺氧化酶的活性，是参与胺的氧化最活跃的一种酶，已引起神经化学和精神病学领域的极大兴趣。首次真正有效的抗抑郁药之一，异烟酰异丙胼，被发现能抑制单胺氧化酶，很明显它能增加大脑的胺，并产生刺激作用以缓解患者的抑郁。这一发现导致了对其它单胺氧化酶抑制剂的研究。

The exact action of tranquilizers, such as chlorpromazine, is not known, but it is theorized that they somehow reduce the permeability of the cell granules that store amines, thus preventing their release and decreasing the concentration of amines in the brain. A decrease in cerebral amines leads to a depression in neural activity, thus producing a calming effect in an anxiety-ridden individual. This depression of nerve activity appears to occur mainly in or near the reticular formation. Barbiturates and anesthetics are known to produce their effects by directly depressing nerve cells of the reticular formation. It is also possible that the enzyme systems of these cells or the blood supply to the reticular formation are affected by these and other drugs.

人们尚不清楚镇定剂的确切作用，例如氯丙嗪，但从理论上说，它们以某种方式降低了贮存胺的细胞颗粒的渗透性，因此，阻止了它们的释放，并减少了脑中胺的浓度。大脑中胺的减少导致神经活动的抑制，从而对焦虑的个体产生了镇定作用。这种神经活动抑郁的出现主要发生在网状结构内或附近。已知的巴比妥类药物和麻醉药通过直接抑制网状结构的神经细胞能产生它们的作用。也有可能，这些细胞的酶系统或对网状结构的供血会受到这些和其它药物的影响。

 Psychedelic Drugs.  Psychedelic drugs, chemicals that affect a person’s perceptions and behavior, have been known to man for many centuries. The religious ceremonies of certain Central American Indians long have included the chewing of peyote cactus, a plant containing the psychedelic drug mescaline. This drug is capable of producing a marked, often dramatic, change in a person’s state of consciousness and perception, with accompanying hallucinations, especially visual ones. Some Mexican Indians achieve the same effect by eating a type of mushroom containing the drug psilocybin. Other hallucination-producing drugs commonly found in plants include marijuana, which is derived from hemp; cocaine, which comes from the cocoa plant; and morphine, which is found in the opium poppy.

迷幻药物。人类了解迷幻药物已有几个世纪，它是影响人的感知和行为的化学物质。某些中美洲的印第安人长久以来的宗教仪式都包括咀嚼佩奥特仙人掌，一种含有墨斯卡灵迷幻剂的植物。这种药物能使人的意识和感知状态产生明显的，常常是戏剧性的变化，伴有幻觉，尤其是视觉幻觉。一些墨西哥印第安人通过食用一种含有裸盖菇素的蘑菇达到同样的效果。在植物中常见的其它致幻剂还包括源自麻类植物的大麻；源自可可植物的古柯碱；以及在罂粟中发现的吗啡。

Much controversy has centered about a hallucinogen of great potency, lysergic acid diethylamide (LSO). LSD is derived from ergot, a fungus that grows on wheat. Ergot has been used in medicine because of its property of constricting blood vessels. It has been useful in controlling bleeding and in stopping attacks of migraine headaches. In limited dosages, ergot does not produce hallucinations.

许多争议都集中在一种有极大潜力的麦角酸酰二乙氨（LSD）。LSD源自麦角，一种长在麦子上的真菌。因为麦角有收缩血管的特性，因此被用于药物。它在控制出血和阻止偏头痛发作中很有用。限制剂量，麦角不会产生幻觉。

In 1943 the Swiss chemist Albert Hofmann was experimenting with an ergot product, lysergic acid. He had altered the molecular structure of the acid, and during his experiments some of the chemical was absorbed into his system, perhaps through the pores of his skin. He described the sensation he experienced as “a very peculiar restlessness which was associated with a slight attack of dizziness … a not unpleasant state of drunkenness which was characterized by an extremely stimulating phantasy … fantastic images of extraordinary plasticity … associated with an intense kaleidoscopic play of colors.” Hofmann later took a second dose, which although it was extremely tiny—only 250’ micrograms—must have been somewhat larger. After this dose, he wrote that he “lost all control of time” and thought he had die. He even saw himself lying dead on a sofa.

1943年，瑞士化学家阿尔伯特·霍夫曼用麦角制品麦角酸进行了实验。他改变了酸的分子结构，就在实验时，他的身体吸入了一些化学物质，也许是通过其皮肤的毛孔。他描述了他体验到的感觉，就像“一种非常不寻常的不安，伴随着轻微的头晕… 一种伴有极为刺激的幻觉，并非不舒服的醉酒状态… 与强烈的万花筒似的色彩有关”。霍夫曼后来进行了第二次服药，虽然剂量很小---只有250微克---但一定是某些东西多了。这个剂量之后，他写道他“失去了对所有时间的控制”，而且他以为他已经死了。他甚至看见自己躺在沙发上死了。

Since Hofmann’s experience, many experimenters have tried LSD, and over a thousand papers have appeared regarding its effects. Apparently the reactions to LSD are individual and remarkably diverse. Some people experience a feeling of gratification and exaltation, while others feel extreme terror. In most, there are visual hallucinations, ranging from spectacular displays of color to grotesque distortions of shape. This has led investigators to believe that LSD acts mainly on the visual cortex.

从霍夫曼的实验之后，许多实验者都尝试过LSD，而且发表过超过一千多篇有关其效果的论文。很明显，对LSD的反应因人而异，而且显著不同。一些人体验了满足和兴奋感，而另一些人感到极为恐惧。在大多数情况下，都出现了视觉幻觉，范围从壮观的色彩展示到形状的奇怪扭曲。这让研究人员相信，LSD主要作用于视觉皮层。

In some subjects taking LSD there is an intensification of emotions, which suggests an effect on the hypothalamus. In a few of these, the intensity of the hallucinations and the emotional stimulation reached such a degree as to imitate schizophrenia. This result has led to the hope that, in some way the cause and cure of this distressing mental disease might be discovered through further experimentation with LSD.

在一些服用了LSD的实验对象中，情绪会加剧，这表明对下丘脑有影响。其中有些实验对象，幻觉与情绪刺激的强度达到了类似精神分裂症的程度。通过用LSD的进一步实验，在某种程度上，这种结果可能为发现这种使人痛苦的精神疾病原因和治疗方法带来希望。

NATURE OF CONSCIOUSNESS

Probably one of the most baffling aspects of brain research concerns the nature of consciousness. Neurophysiologists and neurochemists have yet to find the exact seat of consciousness or to explain how it functions. However, it is likely that the main center for consciousness is located in the reticular formation of the midbrain. The cerebral cortex, even though it has a refining influence on conscious action, depends entirely on the activity of the brainstem as far as consciousness is concerned. Destruction of the cortex may deprive a person of memory, but does not prevent appropriate reactions to external stimuli such as pain, heat, or cold.

意识的本质

脑研究最令人困惑的方面可能与意识的本质有关。神经生理学家和神经化学家们尚未找到意识的确切位置，也无法解释它是如何运行的。然而，意识的主要中枢很可能位于中脑的网状结构中。大脑皮层，即使它对意识的行为具有改善的影响，但就意识而言，它完全取决于脑干的活动。对大脑皮层的破坏会使人丧失记忆，但不会阻碍对外部刺激，如疼痛、热或冷的适当反应。

Most people think of consciousness as merely a state of awareness, in which a person is not asleep, knocked out, or anesthetized. Actually, a conscious act is defined as an act that is thought out on the basis of previous experience. Full consciousness, therefore, depends on the cooperation of the brainstem and the cerebral cortex.

大多数人都认为意识仅仅是感悟能力的一种状态，在这种状态中人没有睡着，昏倒，或麻醉。实际上，有意识的行为可被定义为根据先前的经验想出的行为。因此，完整的意识取决于脑干和大脑皮层的合作。

5. Evolution of the Brain

Through the course of animal evolution the brain has developed from a small clump of nervous tissue in the head region of a flatworm to the highly complex brain of human beings. The most primitive animals, the one-cell protozoa, have no need for a nervous system as is found in multi-cellular animals. Yet even these organisms do have a basic sensitivity or irritability that enables them to avoid excessive heat, harmful chemicals, or obstacles in their path. In addition, paramecia and other ciliates have some type of control mechanism that regulates the beating of their cilia.

5、脑的进化

       在动物进化的过程中，脑从扁虫头部的一小块神经组织发展成人类高度复杂的大脑。最原始的动物，正如在多细胞动物中发现的那样，单细胞原生动物不需要神经系统。然而，即使是这些生物体也有基本的敏感性或应激性，这使它们能够避免过热，有害化学物质，或路途中的障碍。此外，草履虫和其它的纤毛虫拥有某种控制机能来调节它们纤毛的跳动。

The coelenterates were probably the first multi-cellular animals to evolve a definite network of nerves. It has been found that in the jellyfish, as well as other coelenterates, there are synapses at the places where the nerve cells meet each other. In this respect coelenterates resemble higher animals. However, unlike higher animals, jellyfishes and other coelenterates do not have any nervous control center, or brain.

腔肠动物可能是第一批进化出明确神经网络的多细胞动物。人们发现，在水母以及其它腔肠动物中，在神经细胞相互接触的地方有突触。在这方面，腔肠动物类似于高级动物。然而，与高级动物不同的是，水母和其它腔肠动物并没有任何神经控制中枢，也没有脑。

The flatworm (phylum Platyhelminthes) is the most primitive animal to have a definite brain-like structure. In the planarian it is composed of two ganglia, from which short fibers extend to the animal’s eyespots, and two long branching nerve cords extending the length of the body.

扁虫（扁形动物门）是最原始的，拥有明确的类似于脑的结构的动物。在涡虫中，它是由两个神经节组成，从那里，短纤维延伸到动物的眼点，并且两个长分支神经索状结构延伸到身体的长度。

In arthropods the brain is much more complex and has many more functions to perform. In insects, for example, the brain is responsible for synchronizing wing and leg motions and for controlling instinctive and social behavior. In addition, the eyes of insects are very complex, capable of seeing movement as well as light, and the optic lobes of their brain are quite large.

在节肢动物类中，脑要复杂得多，有更多的功能可执行。例如，在昆虫中脑负责翅膀和脚的同步运动，控制本能和社群行为。此外，昆虫的眼睛非常复杂，既能看见运动，也能看见光线，它们脑的视叶很大。

Vertebrates.  Among the vertebrates the most primitive brain is found in the jawless fishes. In these fishes the brain is made up of several definite divisions, including a fairly well-developed medulla and two cerebral hemispheres, each of which is divided into an olfactory lobe and an optic lobe. In the cartilaginous fishes and bony fishes, as well as in the amphibians, the brain is similar to that of the jawless fishes but is somewhat larger with more highly developed olfactory lobes. Because the brains of fishes and amphibians have olfactory lobes that are larger and better developed than the optic lobes, these brains are sometimes referred to as “smell brains,” and these animals indeed possess a keen sense of smell and have relatively poor vision.

脊椎动物。在脊椎动物中，人们在无颌鱼中发现了最原始的脑。在这些鱼类中，脑是由几个明确区域组成的，包括相当发达的髓质和两个大脑半球，其中每半球被分为嗅叶和视叶。在软骨鱼类和硬骨鱼类以及两栖动物中，脑类似于无颌鱼的脑，但它略大点，有更发达的嗅叶。因为，鱼和两栖动物的脑有嗅叶，比视叶更大，更发达，这些脑有时被称为“嗅脑”，而且这些动物确实拥有敏锐的嗅觉以及相对较差的视力。

In reptiles, especially snakes, the olfactory lobes of the cerebrum are still large, but the optic lobes are also large. The reptile’s brain also differs from the brain of a fish or amphibian in that it has a large cerebrum, and in some reptiles the cerebrum is covered with a new kind of tissue. This tissue, called the neopallium, represents the evolutionary beginning of the cerebral cortex.

在爬行动物中，尤其是蛇，大脑的嗅叶依然很大，而且视叶也很大。爬行动物的脑也不同于鱼或两栖动物的脑，因为它有一个更大的脑，而在一些爬行动物中，大脑被覆盖了一种新的组织。这种称为新皮质的组织，代表大脑皮层进化的开端。

Birds are said to have a “sight brain” because their olfactory lobes are very small while the optic lobes are large and well developed. The bird’s cerebral hemispheres are greatly enlarged, but lack any trace of a cortex. The cerebellum, however, does have an outer layer of gray matter.

据说鸟类有一种“视觉脑”，因为它们的嗅叶很小，而视叶较大，且发达。鸟类的大脑半球很大，但却缺乏任何大脑皮层的痕迹。然而，小脑确实有一层灰质的外层。

In mammals, the cerebrum and cerebellum reach their highest development. The mammalian cerebrum fills much of the cranial cavity, covering most of the lower brain regions, and its surface is entirely covered with a layer of gray matter, the cerebral cortex. In a few mammals, including the shrew, the cerebral cortex is smooth, but in most it is convoluted, with many ridges and grooves. This folding of the cerebral cortex was an evolutionary development resulting from a rapid increase in the number of cells making up this layer of gray matter without a corresponding enlargement of the underlying tissue. Although it has sometimes been stated that the number of convolutions in an animal’s cerebral cortex is an indication of the animal’s intelligence, this theory is not true. Some apes, for example, have a less convoluted cerebral cortex than some mammals that have lower intelligence.

在哺乳类动物中，大脑和小脑达到了最高发展。哺乳类动物的大脑占据了大部分颅腔，覆盖了脑下部的大部区域，其表面完全被大脑皮层的一层灰质所覆盖。在一些哺乳类动物中，包括地鼠，大脑皮层是平滑的，但在大多数情况中却是复杂的，带有许多脊和凹槽。大脑皮层的这种褶皱是一种进化发展，是由构成这种灰质层细胞数量的迅速增加，而底层组织没有相应的扩大导致的。虽然有时人说，动物大脑皮层中的卷积数量是动物智力的一种指标，但这种理论并不正确。例如，一些类人猿相比一些智力较低的哺乳类动物，大脑皮层并没有那么多的卷积。

                                       J. EDWARD TETHER, M. D.

                             Indiana University Medical Center

                                    And School of Medicine

                                  J. 爱德华·特瑟，医学博士

                                印第安纳大学警觉中心与医学院

                                           2023年4月22日译

（译者注：该部分词条位列《大美百科全书》1985年版，第4卷，第430页至432页）