BRAIN WAVES (Electroencephalogram, EEG)


Electrical changes, or potentials, occurring during brain activity. The fluctuations are detected through electrodes placed on the skull, and are recorded on a machine known as an electroencephalograph.It has been known for many years that electrical changes taken place in the brain, but it was not until 1929 that a German physiologist, Hans Berger, gave a substantial account of these changes. His original research arose out of an interest in the possibility of extrasensory perception and psychical phenomena, and led to the development of the electroencephalograph, which has enabled investigators to record many types of brain waves and relate them to many aspects of behavior. When electrodes are placed on various parts of the scalp, this sensitive instrument amplifies and registers the slight electrical activity that occurs under different conditions. Recordings from different locations provide a simultaneous comparison of activity in different regions of the brain.Brain waves are analyzed into two components, amplitude and frequency. The amplitude, or height and depth of the wave, represents its electrical strength; its frequency, as expressed in cycles per second (cps) refers to the number of times per second the wave reaches its greatest height and depth. If you stand on the shore watching the ocean, amplitude corresponds to the height of the waves, and frequency to the number of times they strike the beach in a given time.Analysis of EEG recordings indicates that there are several kinds of brain waves, or “Berger rhythms,” although there is no distinct dividing line between the various types. Alpha waves have the largest amplitude and a frequency of about ten to twelve cps. They are typical of normal adults when awake and relaxed, and if they are missing or greatly reduced in number, it is usually a sign of brain dysfunction. Beta waves have a lower amplitude and a frequency of twenty to twenty-five cps at peak strength; if the frequency is slightly lower or slightly higher, they are called “slow beta waves” and “fast beta waves.” Gamma waves have the highest frequency of any recorded on the EEG, reaching forty to fifty cps at peak amplitude. They appear to be part of the beta pattern. Both gamma and beta waves are found primarily in the forward part of the cortex and appear to reflect thinking and reasoning. The so-called “spindle wavesregister twelve to fifteen cps and frequently appear during sleep.Three other types of waves have also been discovered. Delta waves are extremely slow (one to two cps) with a wide amplitude, and appear at irregular intervals during sleep. They seem to arise from deeper regions of the brain, possibly the hypothalamus, and are also believed to stem from areas of the cortex in which there is a lesion or tumor. Theta, or “saw-tooth” waves, with a frequency of four to seven cps, are typically found in young children. The most recent finding is the kappa wave, with a frequency similar to that of alpha waves (ten cps) but a much weaker amplitude. These normally occur while the subject is reading, dreaming, or thinking, and since they are also found in electrical records of eye movements, they are believed to reflect motor activity during thought.The differences between wave types has suggested that the EEG might be extremely useful in investigating both the normal and pathological functioning of the brain. Studies to date indicate that it is a valuable tool, but not so effective as it first appeared to be. Many difficulties have presented themselves. First, the origin of the waves is not always clear, since they seem to involve not only the cortex but deeper parts of the brain. Second, it is hard to pin-point them because they represent the additive effects of thousands and perhaps millions of neurons acting together. Third, it is not known whether they represent a simultaneous, quick burst of activity or a slow, continuous change in the electrical potential of brain cells. Fourth, scientists are not sure whether the brain waves produce changes in behavior or whether changes in behavior produce the brain changes. Nevertheless, research has led to a number of notable discoveries about the activity of the brain under both normal and abnormal conditions.Recent applications of the EEG indicate that there is a wide difference between the wave patterns of different individuals. These patterns appear to be relatively stable for each person, a fact that implies that the EEG is a reliable measure, even though what it measures is not always clear. The patterns, however, change with age. Alpha rhythms are infrequent at birth, but slow seven cps waves coming from the central region of the skull are typical of the newborn child. This is an important fact because slow waves of this type indicate brain damage in an adult but not in children. The adult brain wave pattern is not reached until the child is about nine years old.There are profound differences in the patterns for waking and sleeping, as well as special patterns for drowsiness, light sleep, deep slumber, and dreaming. Alpha waves predominate in waking life, and appear to stem largely from the occipital, or visual, area in the back of the head. When we are drowsy or asleep, trains of delta waves appear. Dreaming has been correlated not only with the return of alpha waves (probably because most dreams are visual), but with recordings of rapid eye movements (Dement and Kleitman, 1957).Although a fairly large percentage of alpha waves occur when a person is awake and relaxed, they disappear and are replaced by fast, low-voltage “activation patterns” when visual and other sensory stimulation occurs. This “alpha blocking” also takes place when changes in stimulation are constantly occurring, as in reading, talking, or watching a movie. If the stimulation continues without change, as with a persistent pain or the ticking of a clock, the alpha waves slowly return. This is believed to reflect the process of adaptation. Studies indicate that the blocking of the alpha waves is due to the reticular activation system, which seems to be the “waking center” of the brain, putting the cortex in a state of readiness for incoming stimulation. See RETICULAR FORMATION.Although much of the research on brain waves is considered experimental and exploratory, some of the findings have been put to practical use in neurology and psychiatry. The EEG is particularly helpful in diagnosing brain lesions, tumors, and epilepsy. Slow alpha waves and saw-tooth theta waves of four to seven cps are indicative of lesions or tumors, and very slow waves of one to three cps are one of the surest signs of damaged tissue. The diagnosis of epilepsy is often difficult since the records of normal people and of epileptics may be almost identical. Nevertheless, certain telltale waves appear in the records of epileptics thirty times more often than in the normal records. Very large and very fast waves occurring in bursts are indicative of grand mal epilepsy; an alternating “spike and dome” pattern in the forward brain areas is symptomatic of petit mal; large, slow, three to six cps waves occur in the psychomotor type of epilepsy in which the patient is afflicted with dream states but has no convulsions. These patterns are most evident during seizures, but less dramatic EEG abnormalities are found between seizures and in individuals who have a predisposition to epilepsy (PLATES 9, 10, 11 AND 12) See EPILEPSY (SYMPTOMS AND TYPES).Many attempts have been made to diagnose mental disorder through EEG records, but the results have not lived up to early expectations. Schizophrenic patients often show slightly faster, weaker, and more irregular waves than normal individuals, but these differences are not consistent. Records taken during the depressive stage of manic-depressive reaction are more normal than different types of personality and differences are not great enough to be indicative (Davis, 1941). Some investigators have found abnormal patterns in antisocial individuals (Hill and Watter- son, 1942). The relationship between different types of personality and different kinds of wave patterns is not definite enough to be useful, although active, mentally awake, and “fidgety” people tend to show much less alpha activity than more relaxed and passive persons. This ties up with the findings on sensory stimulation and alpha blocking. The technique has been of even less value in measuring emotional behavior, reactions under stressful conditions, and changes in behavior produced by tranquilizers and other drugs. If the EEG is to be used with confidence as a tool for personality studies and psychiatric diagnosis, that time is still in the future.

Cite this page: N., Sam M.S., "BRAIN WAVES (Electroencephalogram, EEG)," in, November 28, 2018, (accessed August 15, 2022).


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