3、Electrical Activity of the Brain

The brain is active at all times, even during sleep, and is constantly sending and receiving nerve impulses. Evidence of this electrical activity was first discovered in 1875 by the English physician Richard Caton, who studied the brains of various animals using a crude galvanometer. 1929 the German neurologist Hans Berger, using a more sensitive string galvanometer, was able to demonstrate electrical activity in the human brain and record it on paper. This activity was found to take the form of rhythmic currents, which were recorded on paper as wavy lines. The lines were called brain waves, and the entire recording was called an electroencephalogram, or EEG.

3、脑的电活动。脑在任何时候都很活跃，甚至在睡眠的时候，并持续传递和接收神经脉冲。在1875年，英国医生理查德·卡顿首次发现了这种电活动的证据，他用简陋的检流计研究了各种动物的脑。1929年，德国神经病学家汉斯·贝尔格用一种更灵敏的弦线检流计，已能展示人脑中的电活动，并将它记录在纸上。人们发现，这种记录在纸上，像波浪线一样的活动表现出了有节奏的电流。这些线被称为脑电波，而整个记录被称为脑电图，或叫EEG。

Recording Brain Waves. In recording brain waves, special recording electrodes are placed on the scalp. Each electrode, in addition to picking up the electrical charges of the area directly beneath it, also records charges from nearby brain areas, plus some “background noise” from still more distant areas. Nevertheless, the strongest waves come from the cells closest to the electrode.

记录脑电波。在记录脑电波中，在头皮上放置特殊的记录电极。每个电极，除了获取头皮正下方区域的电荷外，还记录脑部区域附近的电荷，外加一些来自更远区域的“背景噪音”。然而，最强的电波都是来自最靠近电极的那些细胞。

Most often, electrodes are placed on different parts of the scalp, producing simultaneous recordings. Generally, about 8 distinct electrical patterns are recorded at one time. After the recording is made, the waves are measured in terms of amplitude (height) and frequency (number of waves per second, EXPRESSED as cycles per second, or cps).

最常见的，是放置在头皮不同部位的电极所产生的同步记录。通常，一次记录有大约8种不同的电模式。记录完成后，根据波幅（高度）和频率（每秒波数，表示为每秒周数，或叫周/秒）来测量脑电波。

Electrodes are arranged for either mono-polar or bipolar recording. In mono-polar recording one electrode, called the active electrode, is placed near the source of electrical activity, and the indifferent lead, or inactive electrode, is placed on the ear, which is relatively distant from the active electrode. The active electrode then picks up electrical activity of the brain in its near vicinity. In bipolar recordings, both electrodes are placed over active brain regions, and the record obtained is an algebraic resultant of the electrical potentials recorded by each electrode.

布置的电极可用单极，也可用双极记录。在单极的记录中,一个电极被称为活性电极，被放置在电活动源的附近，而非活性电极被放在耳朵上，它离活性电极相对较远。然后，活性电极会在其附近区域获取脑的电活动。在双极的记录中，两个电极都放置在脑的活跃区上面，而获得的记录是由每个电极记录电位的代数结果。

While irregular waves are most prominent in an EEG recording, at times parts of the recording show series of early regular waves. Many of these waves have been found to be related to the subject’s state of alertness and mental activity. They are also related to his state of health, and EEG’s are sometimes useful in diagnosing certain diseases.

虽然不规则的电波在EEG（脑电波图）中是最突出的，但有时一部分记录会显示一系列规则的电波。人们发现，这些许多电波与实验对象警觉性和精神活动的状态有关。它们也与其健康状况有关，而EEG有时对诊断某些疾病很有用。

Types of Brain Waves.  In 1929, Hans Berger found that when a human subject closed his eyes, the EEG recording showed long trains of regular wave with a frequency of 8 to 12 cps. He called these waves alpha rhythm. Berger also found that this rhythm is more prominent in the occipital part of the brain, suggesting that they originate in the visual area of the cerebral cortex. He also noted that when the subject opened his eyes, the alpha rhythm was immediately interrupted. He called this phenomenon alpha blocking and found that it also occurred during concentrated mental activity, as when the subject attempted to do a problem in arithmetic. Thus, Berger concluded that alpha blocking has a definite effect on consciousness and mental alertness.

脑电波的类型。1929年，汉斯·贝尔格发现，当人类实验对象闭眼时，EEG记录以8至12周/秒的频率显示出一长串规则的电波。他将这些电波称为阿尔法节律。贝尔格还发现，这种节律在脑枕部更突出，表明它们起源于大脑皮层的视觉区域。他还注意到，当实验对象睁开眼睛时，阿尔法节律会立刻中断。他将这种现象称为阿尔法阻断，并且发现，在集中的精神活动期间，当实验对象试图做一道算术题时，它又出现了。因此，贝尔格的结论是，阿尔法阻断对意识和精神警觉性具有一种明确的影响。

After Berger’s discovery of alpha waves, other types of regular waves were discovered. One type, called beta wave, has a frequency ranging from 14 to 30 cps. Another type, called delta wave, is much slower, ranging between 0.5 to 5 cps. All THREE types of waves—alpha, beta, and delta—occur at different times during sleep. In the early stages of sleep, or “light” sleep, beta waves of 20 to 24 cps may be seen. During this period there are also bursts of alpha waves (8 to 12 cps). As sleep becomes deeper, large amplitude delta waves appear. Superimposed on these waves is another wave pattern, having a higher frequency and lower amplitude. During the normal 8-hour period of sleep the EEG pattern periodically shifts 4 to 5 times to waves with a higher frequency and a lower amplitude. At these times dreaming is most likely to occur.

在贝尔格发现阿尔法波之后，其它类型的规则波也被发现。一种被称为贝塔波的类型，具有从14至30周/秒的频率。所有三种类型的波—阿尔法、贝塔和德尔塔—在睡眠的不同时间出现。在这个期间，也有阿尔法波的爆发（8至12周/秒）。随着睡眠的加深，会出现大振幅的德尔塔波。叠加在这些波上的是另一种波型，具有更高的频率和更低的振幅。在正常的8小时睡眠时间，EEG模型周期性地随频率较高和振幅较低的波变化4至5次。在这些时间，做梦是最有可能发生的。

Brain wave patterns are also affected by various chemical and physiological changes in the body. If the brain’s blood supply is interrupted even for only 15 seconds, the EEG fails rapidly in amplitude due to the cells’ lack of oxygen. On the other hand, when a patient overbreathes, the carbon dioxide content of the blood fails while the oxygen content increases. The EEG then shows a shift to lower frequency. In addition, a small dose of barbiturates by injection will produce brain waves of a high frequency and low amplitude. If a large injection of a barbiturate is given, delta waves may be seen.

脑电波的模式也会受到身体各种化学和生理变化的影响。如果脑供血中断即使只有15秒，由于细胞缺氧，EEG振幅会迅速衰退。在另一方面，当患者呼吸过度时，血液中的二氧化碳含量会降低，同时氧气含量会增加。然后，EEG会显示一种向较低频率的变化。另外，注射小剂量巴比妥酸盐会产生一种高频率，低振幅的脑电波。如果注射大剂巴比妥酸盐，就可能看见德尔塔波。

Because of its extreme sensitivity to the brain’s electrical activity, the EEG can detect any definite severe damage to the brain, such as that caused by injury or a tumor. Frequently it can also detect epilepsy. It has been found that the brain waves of a person with grand mal epilepsy form a series of characteristic spikes. In patients with petit mal epilepsy a spiked pattern also occurs, but each spike is followed by a dome-shaped wave.

由于它对脑电活动极为敏感，EEG能检测到任何明确的对脑的严重损害，比如由损伤或肿瘤引起的损害。通常，它也能检测到癫痫症。人们发现，一个癫痫发作的人脑电波会形成一系列有特点的脉冲尖峰。在轻度癫痫发作的患者中也会出现一种尖峰模式，但每个尖峰都跟着一个圆顶状的波。

Until recently, research on normal EEG patterns yielded little information other than the subject’s state of alertness. This was largely due to the “background noise,” which has a tendency to disguise many waves that might be valuable in discovering more about the brain’s functioning. In the past several years, new devices, including automatic frequency analyzer and average response computers (ARC), have been used for analyzing the changes in the EEG as a patient responds to various stimuli, such as flashing lights. This sort of research may lead to further knowledge of the inner workings of the neurons of the cerebral cortex. It is know that alpha wave blocking occurs during anxiety, but for the most part relationships between EEG patterns and mental illness have not yet been found.

直到最近，有关正常EEG模式的研究，除了实验对象的警觉状态外，产生的信息很少。这在很大程度上是由于“背景噪音”，它拥有掩盖许多波的倾向，而这些波可能在发现有关脑的更多功能中会很有价值。在过去几年里，新设备，包括自动频率分析仪和平均响应计算机（ARC）已应用于分析患者对各种刺激反应时EEG的变化，比如闪烁的灯光。这类研究可能导致对大脑皮层神经元的内部动作进一步了解。众所周知，焦虑时会出现阿尔法波阻断，但在大多数情况下，尚未发现EEG模式与精神病之间的关系。

                                       2023年4月15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424页至428页）

待续部分： 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）。