14 June 2009

Electroencephalogram

The invention: A system of electrodes that measures brain wave patterns in humans, making possible a new era of neurophysiology. The people behind the invention: Hans Berger (1873-1941), a German psychiatrist and research scientist Richard Caton (1842-1926), an English physiologist and surgeon The Electrical Activity of the Brain Hans Berger’s search for the human electroencephalograph (English physiologist Richard Caton had described the electroencephalogram, or “brain wave,” in rabbits and monkeys in 1875) was motivated by his desire to find a physiological method that might be applied successfully to the study of the long-standing problem of the relationship between the mind and the brain. His scientific career, therefore, was directed toward revealing the psychophysical relationship in terms of principles that would be rooted firmly in the natural sciences and would not have to rely upon vague philosophical or mystical ideas. During his early career, Berger attempted to study psychophysical relationships by making plethysmographic measurements of changes in the brain circulation of patients with skull defects. In plethysmography, an instrument is used to indicate and record by tracings the variations in size of an organ or part of the body. Later, Berger investigated temperature changes occurring in the human brain during mental activity and the action of psychoactive drugs. He became disillusioned, however, by the lack of psychophysical understanding generated by these investigations. Next, Berger turned to the study of the electrical activity of the brain, and in the 1920’s he set out to search for the human electroencephalogram. He believed that the electroencephalogram would finally provide him with a physiological method capable of furnishing insight into mental functions and their disturbances.Berger made his first unsuccessful attempt at recording the electrical activity of the brain in 1920, using the scalp of a bald medical student. He then attempted to stimulate the cortex of patients with skull defects by using a set of electrodes to apply an electrical current to the skin covering the defect. The main purpose of these stimulation experiments was to elicit subjective sensations. Berger hoped that eliciting these sensations might give him some clue about the nature of the relationship between the physiochemical events produced by the electrical stimulus and the mental processes revealed by the patients’ subjective experience. The availability of many patients with skull defects—in whom the pulsating surface of the brain was separated from the stimulating electrodes by only a few millimeters of tissue—reactivated Berger’s interest in recording the brain’s electrical activity.Small, Tremulous Movements Berger used several different instruments in trying to detect brain waves, but all of them used a similar method of recording. Electrical oscillations deflected a mirror upon which a light beam was projected. The deflections of the light beam were proportional to the magnitude of the electrical signals. The movement of the spot of the light beam was recorded on photographic paper moving at a speed no greater than 3 centimeters per second. In July, 1924, Berger observed small, tremulous movements of the instrument while recording from the skin overlying a bone defect in a seventeen-year-old patient. In his first paper on the electroencephalogram, Berger described this case briefly as his first successful recording of an electroencephalogram. At the time of these early studies, Berger already had used the term “electroencephalogram” in his diary. Yet for several years he had doubts about the origin of the electrical signals he recorded. As late as 1928, he almost abandoned his electrical recording studies. The publication of Berger’s first paper on the human encephalogram in 1929 had little impact on the scientific world. It was either ignored or regarded with open disbelief. At this time, even when Berger himself was not completely free of doubts about the validity of his findings, he managed to continue his work. He published additional contributions to the study of the electroencephalogram in a series of fourteen papers. As his research progressed, Berger became increasingly confident and convinced of the significance of his discovery. Impact The long-range impact of Berger’s work is incontestable. When Berger published his last paper on the human encephalogram in 1938, the new approach to the study of brain function that he inaugurated in 1929 had gathered momentum in many centers, both in Europe and in the United States. As a result of his pioneering work, a new diagnostic method had been introduced into medicine. Physiology had acquired a new investigative tool. Clinical neurophysiology had been liberated from its dependence upon the functional anatomical approach, and electrophysiological exploration of complex functions of the central nervous system had begun in earnest. Berger’s work had finally received its well-deserved recognition. Many of those who undertook the study of the electroencephalogram were able to bring a far greater technical knowledge of neurophysiology to bear upon the problems of the electrical activity of the brain. Yet the community of neurological scientists has not ceased to look with respect to the founder of electroencephalography, who, despite overwhelming odds and isolation, opened a new area of neurophysiology.

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