Edgar Douglas Adrian

views updated

Edgar Douglas Adrian

The English neurophysiologist Edgar Douglas Adrian, 1st Baron Adrian of Cambridge (born 1889), shared the Nobel Prize for Physiology or Medicine with Sir Charles Sherrington for their discoveries regarding the functions of neurons.

Edgar Douglas Adrian, born in London on Nov. 30, 1889, was the second son of A. D. Adrian, legal adviser to the Local Government Board. He entered Trinity College, Cambridge, in 1908 and graduated with honors in the natural sciences in 1911. He then embarked on research in physiology, and in 1913 he was elected a fellow of Trinity. Thereafter he took his clinical courses at St. Bartholomew's Hospital, London, and he graduated in medicine at Cambridge in 1915. During the remainder of World War I he studied service men suffering from nerve injuries and nervous diseases, and after the war he lectured on the nervous system at Cambridge. There he was Foulerton research professor of the Royal Society from 1929 until 1937, when he became professor of physiology in Cambridge University.

Early Researches on Single Nerve Fibers

Much experimental work during the 19th and early 20th centuries had shown that, when an isolated motor nerve was stimulated electrically, the resulting nerve impulse not only caused contraction of the muscle associated with that nerve but was accompanied by a change of electric potential (the action current) at the active point of the nerve. This current passed along the nerve at great speed. It was sufficiently strong to be measured by a very delicate capillary electrometer, and the oscillations produced in the mercury level could be recorded by photography on a moving strip of paper. At any point on the nerve the activity lasted for only a few thousandths of a second, and that point became temporarily refractory to further stimulation as soon as the impulse had passed it. In 1909 Keith Lucas proved the important "all-or-none" principle in muscle, that is, in a motor nerve. This principle implied that, in a nerve fibril, a stimulus just strong enough to cause a contraction in the muscle fibers which it supplied produced a maximum contraction in these fibers. In a motor nerve an increase in the stimulus acted by bringing more nerve fibers into action.

By the early 1920s practically all the work in this field had been done on motor nerves because the instruments then available were not sufficiently sensitive to detect the extremely minute impulses produced by the stimulation of sensory nerves. Adrian had been a pupil of Keith Lucas, and before the war, while he was Lucas's assistant, they had discussed the possibility of amplifying the minute currents in sensory nerves and of sensitive methods for recording them. Lucas died in an airplane accident in 1916, and when Adrian returned to Cambridge after the war he began experiments on the lines previously discussed with Lucas. By 1927, using a three-or four-valve amplifier, he had attained a 5000 amplification. By varying the tension in a frog's muscle Adrian showed that the "all-or-none" principle applies also to sensory nerves. But he soon found that his results were influenced by the fact that even the smallest sensory nerves receive impulses from many end organs. It was therefore necessary to study the reactions in single nerve fibers.

The reactions in a single nerve fiber were first demonstrated in 1926 by Adrian, working at Cambridge with a Swedish collaborator. In a frog muscle they were able to dissect out a strip containing a single muscle spindle attached to a single nerve fiber. When this muscle spindle was stimulated by stretching the muscle strip, they obtained a regular series of responses at intervals of 0.03 second. Adrian also found that in all the sense organs that give a prolonged discharge under a constant stimulus—such as muscle spindles and tactile endings—the record shows a rhythmic series of impulses, their frequency depending on the rate of development of the stimulus and on its intensity. In the case of a muscle spindle the frequency therefore depends on the extent and rapidity of the stretch. The stimulus acts as a trigger to release a nerve impulse. The total activity of a fiber can be increased by increasing the frequency of the impulses produced, but not by increasing the strength of the stimulus. The message in a nerve fiber can therefore be varied only by changing the frequency and duration of the discharge.

These experiments also showed that nerves possess the power of adaptation. A steady current passed through a frog muscle produced only one impulse, owing to the very rapid adaptation of the nerve. But steady tension on a muscle spindle, in which adaptation is very slow, produces a succession of impulses in the nerve fiber.

Adrian then turned to the sequence of events in sensory end organs in general. By 1928 he had shown that, in the case of pressure on the skin, the frequency of the impulses varied with the rate of increase of pressure and declined when the pressure remained constant. But when an object touches the skin, there is at that moment a sudden and rapid outburst of impulses, after which the impulses cease. In the case of pain he was unable to obtain clear-cut results or to confirm that pain is due to impulses in specific pain fibers. It seemed possible that pain might be due to very slow impulses.

Activity of Nerve Cells

In 1931 Adrian began to study impulses arising automatically in the brain, for example, in the cells of the respiratory center. In the isolated brain of a goldfish he found the impulses had a regular frequency of 20 to 60 a minute, corresponding in frequency with the gill movements of an intact fish. In an attempt to reduce the number of nerve cells concerned in the reactions, he next investigated the persistent activity that occurs in excised portions of the central ganglia of the water beetle Dytiscus, in which the activity shows the characteristic rhythm of the respiration in that insect. He concluded that the activity of nerve cells is probably due to a slow depolarization of the cell body or its dendrites. The active state in a group of nerve cells implies a surface change like that in the nerve fiber, but, contrary to the momentary change in the nerve fiber, it can persist for long periods and vary in intensity.

It was for the researches described up to this point that Adrian shared the Nobel Prize in 1932.

Rhythm of the Higher Centers

In 1929 Hans Berger discovered that, if electrodes were applied to the head of a conscious subject, a rhythmic disturbance having a frequency of about 10 per second could be recorded. These waves—Berger's alpha rhythm— were often present when the eyes were closed but disappeared when they were opened. The tracing recording the waves was called an electroencephalogram (EEG). About 1934, and later, Adrian studied these waves thoroughly and greatly extended their usefulness in conditions such as epilepsy. He showed that the rhythm occurs essentially in an inattentive subject. If the subject's eyes, when open, gaze at a uniform screen or are covered by glasses that blur the vision, the rhythm decreases only slightly. Adrian found that the waves were produced in a large area of the occipital and parietal regions of the cortex. He also found that, if the subject looked at a screen illuminated by a light flickering at, say, 18 flickers a second, the brain rhythm kept pace with the rate of flicker. In 1934 he also showed that the cerebellum has a spontaneous rhythm of very high frequency waves (150 to 250 per second).

Special Senses and Cortical Representation

A cat, when dropped in any position from a height, always lands on its feet owing to positional impulses received by the vestibular nucleus in the hindbrain. During the war Adrian found that this nucleus reacted to two different kinds of responses, and he studied variations in them induced by changes in the position of the body. In 1943 he studied the impulses received by the cerebellum of a monkey when various parts of its body were moved passively, and he was able to define the different areas in the cerebellum associated respectively with the forelimb, the hindlimb, and the face region.

In 1943 Adrian also studied the relative sizes of the sensory receiving areas of the cerebral cortex connected with different parts of the body in various animals. He found that the size of an area depended on the importance of the information received by it. In humans, the fingers, important in exploring the environment, received generous representation. In the cat the emphasis is on the forelimb, and in the pig the whole of the receiving area appears to be devoted to the snout. In 1946 Adrian found that in the pony and sheep the area devoted to the nostrils is as large as that for the whole of the rest of the body.

Adrian's last writings on neurophysiology (1950-1956) dealt with the olfactory sense. The primary olfactory fibers are so short and thin that it was not possible to record from them, but he obtained records from the olfactory bulb. Deep anesthesia suppressed the spontaneous discharges from the olfactory bulb, and records were then made of the discharges produced by the animal inhaling various odoriferous substances. In the cat he distinguished three different types of discharge, associated respectively with ethereal, oily, and fishy odors. He also obtained important evidence of a process of adaptation in the olfactory nerves.

Later Life

In 1951 Adrian retired from his chair and became Master of Trinity College, Cambridge, an office which he held until 1965. He was vice-chancellor of the University of Cambridge from 1957 to 1959 and chancellor from 1968. He was also the first chancellor of the University of Leicester. In 1942 he was appointed to the Order of Merit, and in 1955 he was created 1st Baron Adrian of Cambridge.

Adrian was the recipient of many honors in addition to his Nobel Prize. In 1923 he was elected a Fellow of the Royal Society. He was its Croonian Lecturer in 1931 and its Ferrier Lecturer in 1938; he received its Royal Medal in 1934 and its Copley Medal—its highest award—in 1946. He served as its Foreign Secretary from 1946 to 1950, and he was president of the society from 1950 to 1955. In 1924 he was elected a Fellow of the Royal College of Physicians of London, and he received several honors in that college. He was president of the Royal Society of Medicine in 1960-1962, and he was awarded that society's Gold Medal in 1950. From 1962 to 1965 he was a trustee of the Rockefeller Institute. He was an honorary fellow of many foreign learned societies, and he received honorary degrees from 33 universities throughout the world.

Throughout his career Adrian wrote numerous scientific articles and published three books, each of which marks a stage in his researches: The Basis of Sensation (1928), The Mechanism of Nervous Action (1932), and The Physical Background of Perception (1947).

On August 4, 1977, Adrian died in London, England. Although he retired from Cambridge in 1965, he continued to live at the college almost until his death. Throughout his life, Adrian was active, enjoying sports such as mountain climbing, fencing, sailing, and bicycle riding. Adrian also took a keen interest in the arts, and particularly enjoyed painting, even meriting an exhibition of 80 of his works at Cambridge.

Further Reading

A short biography of Lord Adrian will be found in Nobel Lectures, Physiology or Medicine, 1922-1941 (1965). This work also contains his Nobel Lecture, which summarizes his earlier work, mainly on single nerve fibers and the end organs. There is a brief discussion of Adrian's work in general in C. Singer and E. A. Underwood, A Short History of Medicine (1962); and a few extracts from his writings are given in E. Clarke and C. D. O'Malley, The Human Brain and Spinal Cord (1968). Reference may also be made to J. F. Fulton, Physiology of the Nervous System (1949). Later biographical material appears in Notable Twentieth-Century Scientists, Volume I (Detroit: Gale, 1995) and Nobel Laureates in Medicine or Physiology (1990), edited by Daniel Fox, Marcia Meldrum, and Ira Rezak. □