BRAIN

The human brain is the most complex and highly specialized organ in the human body. Structurally, it is a mass of nervous tissue, weighting about 3 pounds (1.3 kg) and consisting of more than 10 billion cells. Together with the spinal cord it makes up the central nervous system.

脑

人脑是在人体中最复杂，高度专业化的器官。在结构上，它是一团神经组织，重约三磅（1.3公斤，并包含有超过100亿个细胞。它与脊髓一起构成了中枢神经系统。

A primary function of the brain is to coordinate all of the nervous activity of the body. The brain receives incoming nerve impulses from the eyes, ears, and other sensory organs, analyzes information in the light of past experience, and is responsible for making the necessary adjustments or movements. In addition, the brain is the seat of man’s consciousness, memory, reasoning, and intelligence. It is also the seat of all emotions.

脑的主要功能是协调身体所有的神经活动。脑从眼睛、耳朵和其它感觉器官接受传入的神经脉冲信号，根据过往的经验分析信息，并负责做出必要的调整和运动。另外，脑是人的意识、记忆、推理和智力的处所。它也是所有情感的所在地。

The human nervous system is sometimes compared to a huge telephone system in which there are many millions of miles of wires. If this wire were not connected to a central switchboard, it would be useless. Similarly, man’s peripheral nervous system, which has many miles of nerve fibers, would be of little value if the fibers were not connected with a central coordinating structure, the brain.

有时，人类的神经系统被比作一个巨大的电话系统，在其中，有数百万英里长的线缆。如果这根线缆未连接到中心交换机上，那么它就是无用的。同样，人类的末梢神经系统，也有很长的神经纤维，如果这些纤维未连接到脑的中央协调结构中便没有什么价值。

Brain Cells.  Under the microscope, the brain is found to be composed of two main types of cells: nerve cells, or neurons, and special supporting cells called neuroglia.

脑细胞。在显微镜下，人们发现脑是由两种主要类型的细胞构成的：神经细胞或叫神经元，以及称为神经胶质的特殊支撑细胞。

Formerly, nerve tissue was thought to be composed of two elements: cells and nerve fibers. Now it is known that the cell and fibers are really part of the same unit, the neuron. Each neuron usually consists of a cell body with many thin projections extending from it. At least one of these projections is different from the others. This extension, called the axon, or nerve fiber, may range in length from only a fraction of an inch to many feet and may divide into many branches that are given off at right angles to the main fiber. The body’s longest axon reaches from the brain to muscle controlling the big toe.

以前，神经组织被认为是由两种元素组成：细胞和神经纤维。现在人们已知道，细胞和纤维都是同一个单元神经元的一部分。每个神经元通常包含从其上面延伸出的许多细细突出物的细胞体。这些突出物中至少有一个与其它的突出物不同。这种延伸被称为轴突或神经纤维，长度范围可以从一英寸到许多英尺，并可分为与主纤维成直角发散的许多分支。人体最长的轴突可从脑到达控制大脚趾的肌肉。

Most neurons in the brain and spinal cord have other processes in addition to an axon. These projections, called dendrites, greatly increase the neuron’s receptive surface. They branch repeatedly, and some, such as those in the outer layer of the cerebellum, have a dense brush-like appearance.

除了轴突以外，脑和脊髓中的大多数神经元还有其它的突起。这些突起物被称为树突，大大增加了轴突的接受面。它们不断地分岔，还有一些就像在小脑外层的那些分岔，具有浓密的像刷子一样的外观。

The axons of many neurons are sheathed in a white glistening substance called myelin. Myelin is composed of proteins and lipids (fats) in alternating concentric sheets. Myelinated fibers conduct nerve impulses much more rapidly than unmyelinated ones, and it is believed that myelin is both an insulator and a source of energy for the axon. In a region where there are densely packed myelinated axons, the area is white in appearance and is known as white matter. Areas consisting largely of nerve cell bodies and less myelinated axons are gray in color and are called gray matter.

许多神经元的轴突都被封包在一种称为髓磷脂的白色发光物质中。髓磷脂由蛋白质和呈交替的同心片脂类（脂肪）组成。有髓纤维传导的神经脉冲比无髓纤维快得多，人们认为髓磷脂既是轴突的绝缘本，也是轴突的能量来源。在有髓轴突密集分布的区域，该区域的外观呈白色，被称为白质。那些主要由神经细胞体和较少髓鞘轴突构成的区域呈灰色，被称为灰质。

The neuroglia, or glia cells, form a special supportive and connective network for the brain’s nerve cells, and it is probable that at least some glia cells also have a nutritive function. Glia cells vary greatly in shape and size and it is estimated that there are many times as many glia cells as nerve cells in the brain.

神经胶质或叫神经胶质细胞，为脑神经细胞形成了一个特殊支持和连接网络，而且很可能一些神经胶质细胞至少还具有与营养有关的功能。神经胶质细胞在形状和大小方面差别很大，据估计，神经胶质细胞是脑中神经细胞的许多倍。

Protection.   A structure so important for the functioning of the human body and so fragile as the human brain needs protection from any external damage that may occur. When a nerve cell body is destroyed, the damage is permanent and the cell will never be replaced.

保护。作为人脑，一个对人体功能这般重要又如此脆弱的结构，需要保护免受来自任何外部可能发生的损伤。当神经细胞受到破坏时，损伤是永久的，且损伤的细胞将永远无法替换。

Each day, a few neurons die, and as a person grows older, the blood supply to the brain diminishes, causing more rapid destruction of neurons. Despite this process of cell destruction, the brain is better protected than any other organ in the body. The first line of defense is the bony skull, or cranium, which surrounds the brain and is well designed to withstand injury, for blows tend better to glance off a rounded surface than a flat surface. In addition, the arched surface gives the cranial vault more strength. Even though the outer layer of bone is very thin, there is a spongy layer between the outer layer and an inner layer that can absorb some shock even when the outer layer is fractured.

每一天，都有一些神经元消亡，而随着人年龄的增长，脑供血的减少，造成神经更快的破坏。尽管存在细胞破坏的过程，但脑受到的保护要比身体的其它器官会更好。第一道防线是多骨的颅骨，或叫头盖骨，它围绕着脑且构造精密，可经受住伤害，因为撞击更易于掠过圆形的表面，而非平面。此外，拱形的表面给予了颅顶更强的力量。尽管骨头的外层很薄，但在外层之间有海绵层，而即使在外层断裂时，内层也能吸收一些撞击。

The cranium is actually composed of eight bones which, in the adult, are solidly fused together at fixed or immovable joints called sutures. The bone itself has many openings called foramina, some of which serve as the exits for the cranial nerves. The cranial nerves include the optic nerves to the eyes, the auditory nerves to the ears, the olfactory nerves to the nasal cavities, and many others. At the base of the cranium is a large opening called the foramen magnum, through which the lowest part of the brain passes just before it joins the spinal cord.

实际上，头盖骨由八块骨头组成，在成人中它们是由固定的或称为缝合线的不动关节融为一体。骨头本身有许多称为小孔的开口，其中一些作为脑神经的出口。脑神经包括连接眼睛的视神经，连接耳朵的听觉神经，连接鼻腔的嗅觉神经以及许多其它神经。在头盖骨的底部是一个称为枕骨大孔的开口，在它连接骨髓之前，正好穿过脑的最低部分。

The brain’s second line of defense is furnished by THREE membranes called the meninges, which surround the spinal cord as well as the brain. The toughest of these is the dura mater, which adheres to the inner surface of the cranium. A second membrane, attached to the surface of the brain, is the pia mater. Between these is the THIRD membrane, the arachnoid, which forms a veil-like meshwork. The space between the arachnoid and the pia mater contains the brain’s THIRD line of defense—a clear, watery liquid called the cerebrospinal fluid, which is formed by the choroid plexus, a special group of blood vessels inside the brain.

脑的第二道防线由三层膜组成，称为脑膜，它围绕着骨髓和脑。其中最坚韧的是硬脑膜，它粘附在头盖骨的内表面。第二层膜粘附在脑的表面，是软脑膜。在它们之间是第三层膜，叫蛛网膜，它形成了一种面纱似的网络。在蛛网膜与软脑膜之间的空间包含了脑的第三道防线—一种透明的水状液体，称为脑脊液，它是由脉络丛形成的，一组脑内部的特殊血管群。

The cerebrospinal fluid serves as a shock absorber for the central nervous system and aids in maintaining a fairly constant intracranial pressure. It may also play a role in removing waste materials from the brain and spinal cord, and certain changes in its composition and pressure are valuable in diagnosing diseases of the nervous system. For examination, a sample of cerebrospinal fluid may be obtained by tapping the sub-arachnoid space in the spine just below the end of the spinal cord, a procedure known as a “spinal tap.”

脑脊液作为中枢神经系统的减震器，有助于维持恒定的颅内压。它在清除脑和脊髓中的废弃物中也能发挥作用，而且其成分构成和压力的某些变化对诊断神经系统的疾病很有价值。对检查而言，通过一种称为“脊髓穿刺”的外科手术，穿刺脊髓末端下方蛛网膜下腔，可获得脑脊液样本。

The brain itself is not a solid structure. In its interior are four cavities, called ventricles. These cavities are also filled with cerebrospinal fluid, serving further to cushion the brain against shocks and jolts.

脑本身并不是固态的结构。在其内部有四个腔，称为脑室。这些脑室也充满了脑脊液，进一步让脑免受冲击和颠簸。

Blood Supply.  The neurons of the brain are active day and night, even during sleep, and use up energy at a high rate. In each cell this energy is derived from the oxidation of glucose. Both oxygen and glucose are supplied to the brain cells by the blood delivered through cranial arteries. Because neurons will die if deprived of oxygen or glucose for only a few minutes, the blood supply to the brain is more vital to life than the circulation of blood to any other organ. Although the brain constitutes only 2% of the human body’s weight, it consumes up to 25% of the blood’s oxygen supply. Fortunately, the brains blood supply is so arranged that it is assured a constant circulation even if one of the major vessels is partially blocked.

供血。脑的神经元昼夜都很活跃，甚至在睡觉时也是如此，并以高速消耗能量。在每个细胞中，这种能量来自葡萄糖的氧化。由颅动脉输送的血液将氧气和葡萄糖供给脑细胞。因为，如果失去氧气和葡萄糖仅几分钟神经元就会死亡，所以对生命来说，给脑供血相比器官的血液循环更为重要。尽管脑只构成了人体重量的2%，但它消耗了人体供氧的25%。幸运的是，脑供血是这样安排的，以至于即使一条主血管被部分堵塞，它也能确保持续不断地循环。

The brain is supplied by two pairs of large arteries, the internal carotid arteries and the vertebral arteries. In the neck, the common carotid artery branches just below the angle of the jaw to form the external carotid artery, which supplies the outside of the cranium, and the internal carotid artery, which enters the skull to supply the front half of the brain. This is why pressure applied to both sides of the neck just below the angle of the jaw can cause unconsciousness.

脑由两对大动脉供血，颈内动脉和椎动脉。在颈部，颈总动脉恰好略低于下颌角形成了颈外动脉，它为颅外供血，而颈内动脉进入颅骨为脑的前半部分供血。这就是为什么对下颌角的颈部两边施加压力会导致失去知觉的原因。

The vertebral arteries and their branches mainly supply the back half of the brain. They join with branches of the internal carotid arteries to form an arterial circle, the circle of Willis, at the base of the brain. Thus, if one vessel is blocked, the area normally supplied by the vessel may receive blood by another route.

椎动脉和它们的分支主要对脑的后半部分供血。它们与颈内动脉的分支相连，在脑底部形成了韦利斯氏环的动脉循环。因此，如果一条血管堵塞，通常由该血管供血的区域可通过其它途径接受血液。

The regulation of the blood flow to the brain is mainly achieved by a dilation (widening) or a constriction (narrowing) of the cranial blood vessels in response to the levels of oxygen or carbon dioxide in the blood. If an area of the brain is very active, it uses up more oxygen and releases more carbon dioxide into the blood, causing the vessels to dilate and thus bring more blood into the active area.

流向脑的血液循环主要是通过颅血管的扩张（变宽）或收缩（变窄）对血液中氧气和二氧化碳的水平做出反应。如果脑的区域非常活跃，它会消耗更多的氧气并将更多的二氧化碳释放进血液中，导致血管扩张，从而注入更多的血液到那个活跃的区域。

The arteries of the brain divide into smaller and smaller branches until they become capillaries, the microscopic vessels through which oxygen, glucose, and other substances pass to the neurons. The capillaries then merge into tiny veins, or venules, which converge to from veins that ascend to the brain’s surface and drain into large venous sinuses, cavities that empty into the internal jugular veins. These veins are located on either side of the neck and join with other veins that led to the heart.

脑的动脉会分成越来越小的分支，直至它们成为毛细血管，氧气、葡萄糖和其它物质传到神经元的微血管。然后，毛细血管合并入微小静脉，或小静脉，它从静脉汇集，以至于上升到脑表面并注入大静脉窦，注入颈内静脉的空腔。这些静脉位于颈部的两侧，并与通向心脏的其它静脉汇合。1.      How the Brain Functions

The nerve cells of the brain, like those in other parts of the body, function by means of electrical impulses called nerve impulses. Thus, to understand the functioning of the brain, one must first understand the nature of the nerve impulse. The passage of an impulse over a neuron was formerly thought to be similar to the flow of an electrical current through a wire, but later observations showed that there are two important differences between nerve impulse and an electrical current. First, the speed of a nerve impulse (ranging from 1 to 120 meters—or 31/4 to 395 feet—per second) is extremely slow compared to that of an electrical current, which approaches the speed of light. Second, there is an electrochemical change in the surface membrane of the nerve which, once started, is self-propagating. In other words, the neuron itself supplies the energy for the transmission of the impulse, whereas the electrical wire is only a passive conductor, dependent on a “push” supplied by an external battery or generator to move the electrons.

1、脑如何运作

脑的神经细胞，像身体其它部分细胞一样，通过被称为神经脉冲的电脉冲发挥功能。因此，要理解脑的功能，人们就必须首先理解神经脉冲的性质。脉冲经过神经元的过程以前被认为类似于电流通过电线的流动，但后来的观察表明，在神经脉冲和电流之间有两个重要的差异。第一，神经脉冲（范围从1米到120米—或31/4至395英尺—每秒）的速度与电流的速度相比极慢，而电流接近光速。第二，在神经的表面膜上有一种电化学的变化，一旦开始，它便自动传输。换句话说，神经元本身为脉冲传送提供能量，而电线只是一种被动导体，依靠外部的电池或发电机提供的“推动”来移动电子。

Man’s knowledge of the nature of the nerve impulse has been gained largely through evidence of electrical activity in the neuron and its reaction to electrical stimulation. A nerve fiber may be stimulated by a mild electrical shock applied through a tiny electrode placed on one end of the fiber. This electrical stimulation initiates a nerve impulse that then travels along the fiber. By means of recording electrodes placed further along the nerve, the current can be amplified and observed on an oscilloscope. Through experiments using this technique, it has been found that a neuron, once stimulated, cannot react to further stimulation for a period lasting from 0.0002 to 0.005 of a second. Thus, the theoretical maximum rate at which impulses can be transmitted along a nerve is less than 1,000 meters (3,280 feet) per second, and for about 0.005 of a second after this, a much stronger stimulus is required to reactivate a nerve cell.

人类对神经脉冲性质的认识主要是通过神经元中电活动的证据，以及它对电刺激的反应获得的。通过放置在纤维一端的微小电极，用轻微的电击可以刺激神经纤维。这种电刺激启动了神经脉冲，然后沿着纤维传导。用沿着神经进一步放置的记录电极，在示波器中就能放大和观察到电流。通过使用这种技术的实验，人们发现一旦受到刺激，神经元在持续0.0002 至0.005秒的时间内无法对进一步的刺激做出反应。因此，沿神经传导的脉冲，理论的最大速率小于1000公尺（3280英尺）每秒，此后大约为0.005秒，需要更强的刺激才能重新激活神经细胞。

In the brain, as in all parts of the nervous system, nerve impulses travel over pathways composed of man different neurons. As the impulse is transmitted from the axon of one neuron to the dendrite of the next neuron, it passes over a minute gap called a synapse. It is believed that a nerve impulse is transmitted across a synapse by the release of a small amount of one of several chemical transmitter substances at the tip of the axon. The chemical nature of transmitter substances is not yet known, but it is suspected that a number of different transmitter substances may be present in the brain. There is indirect evidence that acetylcholine and norepinephrine, which are transmitters in the peripheral nervous system, also play a role in the brain.

在脑中，像在神经系统的所有部分一样，神经脉冲通过人类不同神经元组成的各种路径进行传导。当脉冲从一个神经元的轴突传送至下一个神经元的树突时，已经过了一个称为神经突触的极小间隔。人们认为，一个神经脉冲是通过将少量的几种化学之一的传递物质释放到轴突的尖端来传送神经突触的。传递物质的化学性质尚不清楚，但有人猜想，在脑中可能存在一些不同的传递物质。有间接证据表明，乙酰胆碱和去甲肾上腺素在末稍神经系统中是传送器，在脑中也发挥了作用。

The human nervous system consists of thousands of different nerve pathways leading to and from the brain. The relationship of the brain to the rest of the nervous system is similar to that of a computer to the information fed to it from outside sources. However, the brain has a vastly superior “memory bank” than the tapes of the computer, and its output in response to the information sent to it is much more complex. It not only gives the answers, but it also puts them into motion.

人类的神经系统组成了成千上万的，进出脑的不同神经路径。脑与神经系统其余部分的关系类似于计算机与从外部来源为其提供信息的关系。然而，脑相比计算机磁带拥有极其优越的“记忆库”，而它对发送给它信息的响应输出要更加复杂。它不仅要给予回答，而且还要让它们付诸行动。

In the brain, sensory impulses relayed from the peripheral nervous system through the spinal cord and cranial nerves are transmitted from centers in the lower portions of the brain to other lower centers or to cells in the cerebral cortex, the highly developed outer layer of the cerebrum. Here they may be transmitted by special fibers called association fibers to certain “memory cells,” and from there to other cells in the cortex, which then send motor impulses down through the brain and spinal cord to peripheral nerves that stimulate the muscles. All voluntary acts, as well as many involuntary ones, are the result of these THREE basic processes. For example, as a person standing in the street suddenly spies an oncoming car, sensory impulses from his eyes are relayed to the brain’s cerebral cortex. Here, these impulses are interpreted and are relayed to memory cells containing his past experiences concerning traffic safety. From the memory cells, impulses are relayed to other cells of the cerebral cortex and these nerve cells then transmit impulses to the muscles of the legs, making him step back onto the curb in time to let the car pass by. Although this entire process may take only a few seconds, it involves several different nerve pathways and many different nerve cells.

在脑中，通过脊髓脑神经，由周围神经系统传递的感觉脉冲是从脑下方部分的中枢到其它下层的中枢，或高度发达的大脑外层的大脑皮层中的细胞传输的。在这里，它们可以通过称为关联纤维的特殊纤维传输到某些“记忆细胞”，并从那里传输到其它大脑皮层的其它细胞，然后通过脑和脊髓将运动脉冲发送到刺激肌肉的末稍神经。所有的自发行为，以及许多的非自发行，都是这三种基本过程的结果。例如，当站在街上的人突然发现一辆迎面而来的汽车时，他眼睛中的感觉脉冲就被传递到了脑的大脑皮层。在此，这些脉冲就被解释并传递到包含他过往有关交通安全经历的记忆细胞中。从记忆细胞中，脉冲被传递到大脑皮层的其它细胞中，然后这些神经细胞将这些脉冲传递给腿部的肌肉，使他及时退回到路边，让车通过。尽管这整个过程可能只需几秒，但它涉及到几种不同的神经通道和许多不同的神经细胞。

Major Divisions of the Brain

The human brain is composed of THREE major divisions: the cerebrum, the cerebellum, and the brain stem. The brain stem is further divided into four sections: the diencephalon, the midbrain, the pons, and the medulla oblongata (often simply called the medulla). Although each of the various divisions of the brain is generally associated with certain functions, no one part is entirely responsible for any one function. Each division of the brain is interconnected with the others in such a way as to produce an integrated functioning unit.

脑的主要部分

人脑是由三个主要部分组成：大脑，小脑和脑干。脑干进一步分为四部分：间脑，中脑，脑桥和延髓（在许多情况下简称为髓质）。尽管脑的各个部分通常与某些功能有关，但没有一个部分可以负责其它部分的功能。在产生整合功能的单元时，脑的每个部分都以这种方式与其它部分相互连接。

CEREBRUM

The most conspicuous portion of the brain is the cerebrum, which is divided into two cerebral hemispheres by a deep groove, the longitudinal fissure. These two dome-shaped masses fill the greater portion of the cranial cavity, and together weigh about two pounds (0.9 kg), or two THIRDS of the entire weight of the brain. The cerebrum is the portion of the brain that makes the human brain so different from the brains of animals, both in performance and appearance.

大脑

脑中最引人注目的部分是大脑，它由一道称为纵裂的深槽分为两个大脑半球。这两个圆顶状的块占满了颅腔的大部分，加起来的重量约两磅（0.9公斤），或脑整个重量的三分之二。大脑是脑的一部分，以至于无论在性能和外观上都使人脑与动物的脑是如此的不同。

The cerebral hemispheres have been compared in appearance to a walnut kernel, and there is much surface similarity between them. The walnut kernel is protected by a shell, much as the human brain is protected by the bones of the cranium. The walnut kernel is divided into two halves, as is the cerebrum, and the wrinkled surface of the walnut kernel is similar to that of the cerebral hemispheres.

大脑半球在外观上被比作核桃仁，在外观上它们之间有许多相似性。核桃仁得到了壳的保护，非常像人脑被头盖骨保护一样。核桃仁分为两半，大脑也是如此，核桃仁褶皱的表面类似于大脑半球的褶皱。

However, the similarity between the walnut kernel and the cerebral hemisphere disappears when both are sliced with a knife. Inside, the walnut kernel is white underneath its brownish surface. In the cerebral hemispheres there is a dark grayish color extending for a small distance below the surface. This dark grayish matter is the cerebral cortex.

然而，当用刀将两者切成薄片时，在核桃仁与大脑半球之间的相似性便消失了。在内部，核桃仁在其呈褐色的表面下是白色。在大脑半球的表面下，有一种深灰色延伸了一小段距离。这种深灰色的物质就是大脑皮层。

Underneath the cortical gray matter is the cerebrum’s white matter, made up of millions of tiny nerve fibers. Some of these fibers are gathered into an almost solid cable-like structure connecting the two hemispheres. This structure is known as the corpus callosum. Other tracts connect the cortical gray matter with the cerebellum, the midbrain, the medulla, the spinal cord, and many other areas. The interior of each cerebral hemisphere also contains important masses of gray matter, the basal ganglia.

在皮层灰质下是由数以百万计微小神经纤维构成的大脑白质。其中的一些纤维聚集成连接两个半球，几乎实心的索状结构。这种结构被称为胼胝体。其它神经束将皮层灰质与小脑、中脑、髓质、脊髓以及许多其它区域连接起来。每个脑半球的内部也包含重要的灰质团，基底神经节。

Structure of the Cerebral Cortex.  The cerebral cortex has an area of nearly 2% square feet (0.2 sq meters), of which only about one THIRD is found on the outside of the cerebrum. The remaining portion of the cerebral cortex lines the various grooves and fissures of the cerebral hemisphere. In addition to the longitudinal fissure, which separates the two hemispheres, there are two fissures in each hemisphere: the fissure of Rolando and the fissure of Sylvius. These fissures divide each hemisphere into four lobes, which are named according to the bones of the skull adjacent to them. They are the frontal, parietal, temporal, and occipital lobes.

大脑皮层的结构。大脑皮层拥有一个接近2%平方英尺的面积（0.2平方米），其中大约只有三分之一位于大脑之外。大脑皮层的其余部分都分布在大脑半球的各凹槽和裂隙中。除了将两个半球分开的纵裂外，在每个半球也有两个裂隙：罗朗多氏裂隙和西尔维厄斯氏裂隙。这些裂隙将每个半球分为四个脑叶，它们都是根据毗连它们的脑颅骨命名的。它们是额叶，顶叶，颞叶和枕叶。

The grooves of the cerebral cortex are called sulci, and the ridges between them are called gyri or convolutions. This convoluted arrangement of the cerebral cortex allows a greater amount of gray matter to fit into the available space. If the cerebral cortex were not convoluted into many folds but were spread out flat, it would cover an area of about 324 square inches.

大脑皮层的凹槽被称为脑沟，而在它们之间的隆起纹路被称为脑回或脑回旋。大脑皮层的这种复杂排列允许大量的灰质适应可用的空间。如果大脑皮层没有盘绕成许多皱褶的话，那么它会覆盖大约324平方英寸的面积。

The thickness of the cerebral cortex varies greatly depending on its location. It is always thicker at the top of a convolution and gradually diminishes as it reaches the bottom of a sulcus. The average thickness is about 1/10 of an inch.

大脑皮层的厚度因其所在的部位差别很大。它总是在脑回旋顶部时更厚，而当它到达脑沟底部时逐渐变薄。平均厚度约为一英寸的十分之一。

In addition to the many nerve fibers, neuroglia, and blood vessels, the cerebral cortex contains the cell bodies of many billions of neurons. Under the microscope, most of the cerebral cortex is seen to be made up of six definite layers. These layers, as they occur from the outside to the inside, are as follows:

除了许多神经纤维、神经胶质和血管外，大脑皮层包含了数以亿记神经元的细胞体。在显微镜下，观察到的大脑皮层是由六个明确的层组成。因为它们是从外向内发生的，这些层如下：

     Layer                      Composition

      层                         成分构成

Molecular            Only a few small cells; many fibers.

分子                只有几个小细胞；许多纤维。

Outer granular        Tightly packed small cells; few fibers.

外颗粒层            紧密排列的小细胞；纤维不多。

Pyramidal            Large pyramid-shaped cells; many fibers.

锥体                大的锥体状细胞；许多纤维。

Inner granular         smaller, star-shaped cells; many fibers.

内颗粒层            更小的，星状细胞；许多纤维。

Inner pyramidal        giant pyramid-shaped cells, especially in motor cortex.

内锥体               巨大的锥体状细胞，尤其是在运动皮层中。

Fusiform              Tightly packed small spindle-shaped cells.

梭状                 紧密排列的小梭状细胞。

 

The axons of cortical cells may be divided into THREE types according to their destination and function. Projection fibers are those that go to other areas of the nervous system. An example of a projection fiber is a motor cell axon that goes to the spinal cord. Association fibers make connections with other neurons in the same hemisphere. These are, by far, the most numerous, indicating that the great majority of cortical cells are concerned with the function of association. Commissural fibers connect to neurons in the opposite hemisphere, enabling one hemisphere to communicate with the other.

皮层细胞的轴突可根据它们的目标和功能分为三种类型。投射纤维是那些通向神经系统其它区域的纤维。投射纤维的一个例子是通向脊髓的运动细胞轴突。关联纤维与在同一半球的其它神经元连接。到目前为止，这些是数量最多的，表明绝大多数的皮层细胞与关联的功能有关。连合纤维连接着对面半球的神经元，能使一个半球与另一个半球沟通。

All of the cortical cells also possess dendrites that project both vertically and horizontally. Axons of other nerve cells join these dendrites at synapses, producing complex cortical circuits. This is especially so of the small cortical cells that are most numerous in the human brain.

所有的皮层细胞都拥有垂直和平行投射的树突。其它神经细胞的轴突在突触处与这些树突相连，产生复杂的皮层回路。人脑中数量最多的小皮层细胞尤其如此。

Functions of the Cortex.  The THREE major functions of the cerebral cortex—associative, sensory, and motor—correspond to different areas of the cortex. The sensory regions of the cortex interpret impulses from the eyes, ears, taste buds, nose, and special receptors in the skin. The voluntary control of muscular movements is an important motor function of the cerebral cortex. The movements stimulated by impulses from the motor cortex are modified by another area of the cortex, producing a sense of movement and an orientation of the various parts of the body with respect to one another. This sense is known as the kinesthetic sense.

大脑皮层的功能。大脑皮层的三个主要功能—关联、感觉和运动—对应大脑皮层不同的区域。大脑皮层的感觉区域解释来自眼睛、耳朵、味蕾、鼻子和皮肤中特殊接受器的脉冲。肌肉运动的自主控制是大脑皮层的一种重要运动功能。通过运动皮层脉冲刺激的运动由大脑皮层的另一个区域来修正，使身体的各部位彼此相对产生运动感和方向感。这种感觉被称为动觉感。

The associative functions of the cerebral cortex make man the most intelligent of all animals. These functions endow man with conscious thought, judgment, reasoning, willpower, and memory. Intelligence develops partly by means of stored IMPRESSIONS received by the special senses of sight, hearing, smell, taste, and touch. These stored IMPREESSIONS (memories) can usually be recalled at will to a conscious level. Some memories often last a lifetime, suggesting that long-term or remote memory depends on a type of permanent change that occurs in neurons. Recent or short-term memory is somewhat less stable.

大脑皮层的关联功能使人类成为所有动物中最聪明的动物。这些功能赋予了人类有意识的思维、判断、推理、意志力和记忆。智力的发展在某种程度上是通过特殊的视觉、听觉、嗅觉和触觉，凭借储存的印象获得的。这些贮存的印象（记忆）通常会以一种有意识的层面随意被回想起来。一些记忆常常伴随一生，这表明长期或遥远的记忆依赖于神经中出现的一种永久变化。近期或短期的记忆并不稳定。

It is now recognized that no single area of the cerebral cortex alone is responsible for the total intellectual capacity of the brain. If the entire cerebral cortex is removed from an animal’s brain, the animal will eat, respond to loud noises or light, but will show no real intelligence. However, it will EXPRESS rage and fear because as its lower centers, especially the thalamus and hypothalamus, are no longer controlled by higher brain levels, its emotional reactions will become uninhibited.

现在已认识到，大脑皮层中没有哪个单独区域可以负责脑的全部智力。如果从动物的脑中祛除整个大脑皮层，那么动物会吃，会对噪音和光线做出发反应，但不会表现出真正的智力。然而，它会表达愤怒和恐惧，因为作为其低级中枢，尤其是丘脑和下丘脑，不再受高级脑层级的控制，其情绪反应会变得不受控制。

Motor Function.  The motor areas of the cerebral cortex occupy a long band of tissue in the posterior part of the frontal lobe, on the front lip of the fissure of Rolando. The ridge occupied by the motor cortex is called the precentral gyrus. By electrically stimulating the brains of anesthetized animals and humans undergoing brain operations, it has been possible for scientists to map out the motor areas of the cortex, showing which areas control which body muscles. These studies have shown that the centers for the various muscle groups are arranged in an order opposite to that of the muscles in the body. The areas concerned with the muscles moving the knee joint are at the top, while those concerned with movements of the toes are over the top, in the longitudinal fissure on the surface of the hemisphere. Those motor areas responsible for moving the jaws, tongue, and throat are lowest, on the lateral surface of the cerebral hemisphere. In between these areas are the centers controlling the muscles of the hip, trunk, shoulder, arms, hand, and face.

运动功能。大脑皮层的运动区域在罗朗多氏裂隙的前缘上占用了额叶后部的一长条组织。由运动皮层占用的隆起部分被称为中央前回。通过电方式刺激被麻醉的，接受脑部手术的动物和人的大脑，科学家就可以绘制出大脑皮层的区域，显示哪些区域控制着哪些身体肌肉。这些研究表明，各种各样肌肉群的中枢排列顺序是与身体肌肉的顺序相反的。涉及运动膝关节肌肉的区域在顶部，而与脚趾运动有关的那些区域穿过顶部，位于半球表面的纵向裂隙中。这些负责移动下颌、舌头和喉咙的运动区域位置最低，在大脑半球的侧面。在这些区域之间是控制臀部、躯干、肩膀、双臂、手和脸部肌肉的中枢。

In the motor areas are found the giant pyramidal cells, or Betz cells. These cells give rise to axons which make up the larger fibers of the corticospinal, or pyramidal, tracts. These tracts descend through the midbrain, pons and medulla into the spinal cord. At the junction of the medulla and spinal cord, however, most of the tracts from the left cerebral hemisphere cross over to the right side of the spinal cord while most of the fibers from the right cerebral hemisphere cross over to the left. This crossover explains why damage to one side of the motor cortex will almost always affect the muscles on the opposite side of the body.

在运动区域发现有大锥体细胞，或叫贝兹细胞。这些细胞产生出轴突，构成皮质脊髓束，或锥体束，神经束的更大纤维。这些神经束向下通过中脑、脑桥和髓质进入脊髓。然而，在髓质和脊髓的交汇处，来自大脑左半球的大多数神经束交叉到脊髓的右侧，而来自大脑左半球的大多数纤维交叉到左侧。这种交叉就解释了为什么一侧运动皮层受伤几乎总是影响到身体另一边肌肉的原因。

The pyramidal cells and their axons are known as upper motor neurons. Their destination is the lower motor neurons, the cells of the spinal cord that are directly concerned with the motor nerves leading to muscles.

锥体细胞和它们的轴突被称为上运动神经元。它们的目标是更低的运动神经元，脊髓的那些细胞直接与导致肌肉的运动神经有关。

Sensory Functions.  Across the fissure of Rolando, in the anterior part of the parietal lobe, is the postcentral gyrus. This is the main area of the cortex for body sensations, and it is called the somesthetic area. The centers for sensory impulses arising from various regions of the body correspond to those of the motor areas on the precentral gyrus. The area for sensations from the foot is at the tip, while those for the leg, trunk, arm, and hand are placed below, in that order.

感觉功能。穿过罗朗多氏裂隙，在顶叶的前部是中央后回。这是大脑皮层负责身体感觉的主要部分，被称为躯体感觉的区域。来自身体不同区域的感觉脉冲中枢与中央前回运动区域的那些中枢相对应。脚的感觉区域在顶端，而负责腿、躯干、臂和手的那些中枢按顺序被排列在下面。

The somesthetic area is concerned mainly with sensations of touch and taste. It also receives impulses from sensory receptors in muscles and joints (kinesthetic sense). In additions, it is responsible for discriminating between stimuli of different intensities.

躯体感觉的区域主要是涉及触觉和味觉。它也接收来自肌肉和关节（动觉感）感觉接受器的脉冲。此外，它还负责区别不同强度之间的刺激。

The sensory area of the post-central gyrus does not receive all sensory impulses. Impulses for hearing are received by centers in the upper temporal lobe, while the centers for vision are located in the occipital lobe, and those for smell are located in the front portion of the temporal lobe.

中央后回的感觉区域并不接收所有的脉冲。听觉脉冲是由位于颞叶上部的中枢接收的，而负责视觉的中枢位于枕叶，而且那些负责嗅觉的中枢则位于颞叶的前部。

Pain, temperature, and some sensations of contact are not primarily received by the somesthetic cortex. These are apparently perceived in the thalamus.

疼痛、温度以及一些接触的感觉并不是主要由感觉皮层接收的。这些明显是由丘脑感知的。

Associative Functions—Memory.  Scientists have attempted to duplicate one of the brain’s most important associative functions, memory, by means of a computer. The computer has a useful “memory bank,” but the “memory” of a computer is not at all like the memory of the human brain. When part of a computer’s “memory” is destroyed nothing remains. However, when large areas of the brain are destroyed, definite memories remain. This would seem to indicate that brain memory is stored in large regions of the brain as a diffuse process, rather than in localized cells or lobes.

关联功能---记忆。科学家试图通过计算机复制一种脑最重要的关联功能，记忆。计算机拥有一个有用的“内存库”，但计算机的“内存”完全不像人脑的记忆。当计算机的“内存”部分被破坏时，便什么都不剩了。然而，当脑的大范围受损时，确定的记忆依然存在。这似乎表明，脑的记忆是以一种弥散的方式储存在脑的广大区域中，而不是储存在局部的细胞中，或脑叶中。

Of the many billions of nerve cells in the cerebral cortex, by far the great majority are utilized in associative memory. These cells are linked together in chains by billions of association fibers. These cells and fibers may be reused indefinitely; each time they are used, impulses cross their synapses with greater ease. Memories stored in some cells can thus associate with those stored in others, and new IMPRESSIONS can be compared with memories of previous IMPRESSIONS. Thus logical conclusions can be reached and these can further result in creative thinking.

在大脑皮层数以亿计的神经细胞中，到目前为止，绝大多数都用于关联记忆。这些细胞由数亿个关联纤维的链连在一起。这些细胞和纤维可无限地重复使用；每次使用它们时，脉冲会更容易穿过它们的突触。储存在某些细胞中的记忆因此会与储存在其它细胞中的记忆相互关联，而且新的印象可以与先前印象的记忆进行比较。因此，可得出符合逻辑的结论，并且这些还可以进一步产生创造性的思维。

Memories are compounded from IMPRESSIONS received as stimuli in various sensory areas of the postcentral gyrus. Here, they are received as sharply defined sensations, such as that of vision or touch. These sensations are then relayed to parasensory areas, which combine and elaborate them into more complex IMPRESSIONS, which may be recalled under certain conditions. From here they may go to more distant association areas where they may be combined with other IMPRESSIONS, such as those of form, size, and texture. Thus, the memory of an object that has been previously seen and felt is stored so that if seen again, it is recognized. Recognition has been defined as the matching of an object being perceived to a memory of its previous perception.

记忆是来自作为中央后回的各个感觉区域刺激所接收的印象而合成的。在这里，它们被作为清晰的感觉来接收，比如视觉和触觉。然后，这些感觉被传送到副感觉区，将它们组合并细化成更复杂的印象，这些印象在某种情况下可被回忆起来。从这里，它们可以去更远的关联区载，在那里，它们可与其它的印象相结合，比如形状、大小和质地的印象。因此，以前看过和感觉到的物体印象被储存起来，所以，如果再见到便可认出来。识别被定义为对感知物体与之前感知记忆的匹配。

Although memories are stored diffusely throughout the brain, it is thought that the more complex memory patterns are located in the temporal lobe. However, some investigators believe that these are transmitted to the prefrontal area where they are synthesized into complex patterns and form the basis for abstract thought.

尽管记忆是以弥散的方式储存在整个脑中，但有人认为，更为复杂的记忆模式位于颞叶中。然而，一些研究者认为，这些记忆传到前额叶区，在那里它们被合成为复杂的模式，并形成了抽象思维的基础。

The prefrontal areas also receive many association fibers from the thalamus, a center concerned with emotions. Thus, these prefrontal areas are thought by some scientists to have a conditioning or modifying effect on emotional reactions and their EXPRESSION. Evidence of this has been shown in patients who have undergone a lobotomy, an operation in which the fiber connections of the prefrontal areas are severed. In psychotic patients this operation has sometimes been successful in relieving their anxieties. The operation has also been performed on patients who have prolonged intractable pain. Such patients, although they apparently still feel pain after the lobotomy, are better able to bear it as they no longer seem to have any anxiety or fear about it. Patients who have had lobotomies, however, although retaining memory, seem to have less initiative and judgments, and are more easily distracted. They seem to have some impairment in mental concentration and cannot sustain intellectual effort. Many patients who have had lobotomies also seem to have less control of their emotional behavior.

前额叶区也承接来自丘脑，与情感中枢有关的许多关联纤维。因此，一些科学家认为，这些前额叶区对情感的反应和它们的表达具有一种调节或修正的作用。接受了前脑叶白质切除术的患者已证明了这点，一种切断前额叶区纤维连接的手术。在精神病患者中，这种手术有时能成功地缓解他们的焦虑。对于有长期顽固性疼痛的患者也可进行这种手术。据说，尽管他们在前脑叶白质切除术后依然感到疼痛，但这样的患者能更好地承受它，因为他们似乎不再对它有任何焦虑或恐惧。然而，做过前脑叶白质切除术的患者，尽管保留了记忆，但似乎少了些主动性和判断力，且注意力更容易分散。他们似乎在精神集中方面有某些障碍，无法保持智力活动。许多已做过前脑叶白质切除术的患者对他们的情绪行为似乎也缺乏控制。

 Memory mechanisms appear to entail two different phases or processes. One is an early process that lasts up to an hour, during which time the memory may be erased by electrical shocks or injury to the brain. An example of this type of memory loss is the lack of memory of events occurring a short time before a person suffers a brain concussion. Such shocks or injuries, however, do not affect the second process, called remote memory. A person may not always be conscious of this type of memory, but under hypnosis, long-forgotten episodes can be recalled in detail. Under hypnosis, a person can be regressed by years, even to the stages of early childhood, so that he writes and speaks in a childish manner. He may remember certain birthday parties in detail: who attended, presents received, and even the day of the week on which the party occurred. In addition to hypnosis, electrical stimulation of the temporal lobe during brain surgery can be used to recall complicated memories complete with sights and sounds.

记忆机制似乎涉及两个不同的阶段或过程。一个是持续一小时的早期过程，在这段时间里，大脑因电击或损伤，记忆可能被清除。这种记忆丧失的例子是，人在遭受脑震荡前对短时间内发生的事件缺失了记忆。然而，这样的电击或损伤并不影响被称为久远记忆的第二个过程。一个人不可能总是意识到这种记忆，但在催眠状态下，长久遗忘的那些经历可能会被详细地回忆起来。在催眠状态下，一个人可能随着岁月的倒退，甚至是倒退到儿童的早期阶段，所以他会以幼稚的方式写东西和说话。他可能会详细地记起某些生日聚会：谁参加了，收到的礼物，甚至是举办聚会的星期几。除了催眠外，在脑部手术期间对颞叶的电刺激可以用来回忆包括视觉和声觉的复杂记忆。

The mechanism by which brain cells store memories is not clearly understood. According to one theory, a permanent change occurs in the synapses. Another, more recent, theory states that there are changes in the cells’ RNA (ribonucleic acid) molecules, and since RNA molecules play an important role in the cells’ synthesis of proteins, it is believed that memories are stored in “coded” proteins.

脑细胞储存记忆的机制目前尚不清楚。根据一种理论认为，在突触中发生了永久变化。另一种更新的理论认为，细胞的RNA（核糖核酸）分子发生了变化，并且由于RNA分子在细胞合成蛋白质中起到了重要作用，认为记忆是储存在“编码的”蛋白质中。

Learning. Learning is made possible by two functions of the brain: memory (the ability to recall past IMPRESSIONS and experiences) and association (the ability to relate memories to present situations). There are two main types of learning: conditioned response and operant learning.

学习。大脑的两个功能使学习成为可能：记忆（回想起过去的印象和经历的能力）和关联（使记忆与现状联系起来的能力）。学习有两个主要类型：条件反射和操作性学习。

The experiments of the great Russian scientist Ivan Pavlov (1927) present an example of conditioned response. In Pavlov’s experiments meat juice was injected into a dog’s mouth, and the dog’s flow of saliva then was measured. Later, a bell was rung or a light was flashed just before the meat juice was given. After this procedure was repeated a number of times, the dog’s saliva began to flow whenever the bell was rung or the light was flashed. This type of response is called a conditioned response.

伟大的俄罗斯科学家伊万·巴普洛夫（1927年）的实验呈现了一种条件反向的例证。在巴普洛夫的实验中，将肉汁注入狗的嘴中，然后测量狗的唾液流量。之后，在喂肉汁之前响起铃声或亮灯。在这个过程之后，不断地重复，当铃声响起或亮灯时，狗就会开始流唾液。这种反应被称为条件反射。

Conditioned response is considered to be passive conditioning in contrast to operant learning, which is active. In operant learning, the reward is dependent on what the learner consciously or purposely does. Simple examples of operant learning are seen every day. A dog, for example, sits up or barks for food, or a seal balances a ball on its nose in exchange for a fish. Factors affecting operant learning include inborn mental capacity, experience, need, motivation, goals, emotional conditioning, attitudes and values, active participation, and concentration.

条件反射被认为是与积极主动的操作性学习相反的被动条件训练。在操作性学习中，奖励取决于学习者有意识地或有目的地的行为。人们每天都能看到简单的操作性学习。例如，一只狗为食物端坐或吼叫，或一只海豹为换取一条鱼用鼻子平衡一只球。影响操作性学习的因素包括天生的心智能力、经验、需求、动机、目标、情绪条件、态度与价值观、积极的参与和专注。

Creative thinking differs from routine learning in that it goes far beyond the mere understanding of a problem or a condition perceived by the sense organs. Creative thinking involves a search through the backlog of prior learning experiences and a reorganization of these IMPRESSIONS into new and original patterns of thought.

创造性思维不同于常规学习就在于它远远超越了仅仅是对问题的理解，或由感官器官感知的状态。创造性思维包含搜索先前学习经验的贮备和将这些印象重新组合成新的和原始的思维模式。

Basal Ganglia.  At the base of the cerebrum, close to the diencephalon, are several gray masses, the basal ganglia. These ganglia include the amygdaloid nucleus, the claustrum, and the lenticular and caudate nuclei. Both the lenticular and caudae nuclei, together with the internal capsule separating them, are called the corpus striatum. The corpus striatum has connections from the motor and pre-motor frontal cortex to the thalamus. It also has connections to motor cell bodies of certain cranial nerves.

基底神经节。在大脑的基底，接近间脑的位置是一些灰质核团，基底神经节。这些神经节包括杏仁核、屏状核，豆状核和尾状核。豆状核和尾状核，连同分开它们的内囊，被称为纹状体。纹状体将运动和前运动额皮层连接到丘脑。它还将某些颅神经的运动细胞体相连接。

The corpus striatum and some associated basal ganglia play an important role in extra-pyramidal motor control, but they are, however, dominated by the motor cortex. They exert some control over postural adjustment, smooth locomotion, facial EXPRESSION, and semiautomatic movements such as the swing of the arms in walking. Because these functions are all disturbed in a disorder known as paralysis agitans, or Parkinson’s disease, the disease is thought to be due to an imbalance in this area.

纹状体和一些关联的基底神经节在锥体外运动控制中起到了重要作用，然而它们是由运动皮层支配的。它们对姿势调整、平稳运动、面部表情以及诸如在行走中手臂的半自主动作都施加了一些控制。因为，这些功能在一种被称为震颤性麻痹紊乱或称为帕金森的疾病中都被打乱了。该疾病被认为是由于这个区域的不平衡所致。

The amygdaloid nucleus has connections with the olfactory cortex and the hypothalamus. Damage to the amygdaloid nucleus in certain animals produces certain emotional and sexual changes.

杏仁核与嗅皮质和下丘脑有联系。伤及某些动物的杏仁核会产生某些情绪和性取向的改变。

                                    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8日译

（译者注：该词条部分位列《大美百科全书》1985年版，第4卷，第419页至424页）

待续部分：DIENCEPHALON间脑（Thalamus丘脑；Hypothalamus下丘脑）; MIDBRAIN中脑；CEREBELLUM小脑（Functions功能）；PONS脑桥；MEDULLA髓质；RETICULAR FORMATION网状结构；CRANIAL NERVES颅神经；3、Electrical activity of the Brain脑的电活动（Recording Brain Waves记录脑电波；Types of Brain Waves脑电波的类型）；4、Brain Research 脑研究；STUDIES OF BRAIN FUNCTION对脑功能的研究；BIOCHEMISTRY OF THE BRAIN脑的生物化学（Amino Acids氨基酸；Enzymes and Amines酶与氨基酸；Psychedelic Drugs引起幻觉的药物）；NATURE OF CONSCIOUSNESS意识的性质；5、Evolution of Brain脑的进化（Vertebrates脊椎动物）。