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Hess, Walter Rudolf


(b. Frauenfeld, Switzerland, 17 March 1881; d. Locarno, Switzerland, 12 August 1973),

autonomic nervous system, diencephalon, haemodynamics, hypothalamus, ophthalmology, physiology, thalamus.

In 1949, Hess won the Nobel Prize in Physiology or Medicine for his work in discovering the role certain parts of the brain play in determining and coordinating the functions of internal organs. In particular, Hess was interested in the autonomic nervous system, those nerves extending from the seat of the brain through the spinal cord that control the automatic functions of the body, such as digestion, respiration, and excretion. These nerves can also trigger the activities of a group of organs responding to complex stimuli, such as stress.

An old-fashioned generalist in physiology, Hess studied a wide range of biological phenomena beyond the functional capacities of the diencephalon (interbrain), including the reflex properties of the human circulatory system, the connections between the circulatory and respiratory systems, the brain’s links to psychiatric disorders, the mechanisms of sleep, the oculomotor system, how psychotropic drugs affect the brain, and the biological correlates of consciousness.

Early Intellectual Life . Walter Rudolf Hess was born in Frauenfeld, a small German-speaking town on the eastern side of Switzerland, on 17 March 1881. He began attending secondary school there at the age of twelve, graduating in 1900. His father Clemenz Hess, a tremendous influence on Hess’s early love of the life sciences, taught physics in the local college. With his father’s help, Hess collected and cataloged plants and butterflies from the fields around his home. These experiences fed his interest in the functional traits in the biological world around him, and taught him as well the skill of careful observation and documentation. Hess also worked for his father, setting up experiments for his physics students in his classes.

Wanting to explore new traditions and customs, Hess started medical school at the University of Lausanne, in the French-speaking area of Switzerland. He then spent a semester in the capital city of Bern, and finally completed his courses and passed his exams at the University of Zürich in 1905. Hess also studied medicine at the universities in Berlin and Kiel.

It was during his time in Zürich that Hess first published scientific research. During an anatomy class, the instructor pointed out to Hess an anomaly in how the arteries are formed in the foot. Not satisfied with the reason his teacher gave for this anomaly, Hess devised his own explanation based on the relationship between hemo-dynamics, or blood dynamics, and the morphogenesis of the human arterial system. Hess eventually discussed this idea with Wilhelm Roux, a well-known anatomist at the nearby University of Halle, who encouraged Hess to submit this idea as an article to Archiv für Entwicklungsmechanik, of which Roux was editor.

Though he would have preferred to study theoretical medicine, which would have entailed an unpaid residency at a university clinic, Hess for financial reasons chose a paid residency in the state hospital of his home canton. There he worked under Dr. Konrad Brunner, a skilled and well-known surgeon. Now being able to see the vascular system in vivo, Hess’s fascination with it and hemo-dynamics intensified.

He became aware that contemporary science paid more attention to the pumping action of the heart than to things such as blood viscosity and resistance. To fill this lacuna, Hess decided to build an apparatus that could measure blood viscosity for clinical use. This device became known as a Hess viscosimeter and soon was found in medical laboratories everywhere. His medical thesis in 1906 outlined how the internal resistance of blood might influence the efficacy of the heart and the circulatory system and argued that scientists would do well to focus more attention on the blood’s properties.

Hess wanted to specialize in a branch of medicine that would allow him to pursue basic research on the side. Ophthalmology struck him as the ideal choice. Consequently, Hess became a resident in the department of ophthalmology at the University of Zürich under Professor Otto Haab in 1906. Though Hess was less than taken with the purely morphological approach in his new department, he did learn how to operate with precision, and he did get the chance to study the ocular system dynamically by diagnosing oculomotor disturbances. Through his work with patients with oculomotor pathologies, Hess saw the need to develop a method that would enable doctors to measure eye muscle coordination objectively instead of depending on unreliable verbal reports. The apparatus he devised is still used in modified form under the name Hess screen. Hess’s interest in the oculomotor system reemerged later in his life in his study of the general principles behind sensorimotor coordination.

By the time World War I started, Hess had completed his residency in ophthalmology, studied for a brief period in Paris, and had taken over the practice of an ophthalmologist in Rapperswil, a small city near Zürich. In the spring of 1908, Hess married his fiancée, Louise Sand-meier, who had worked as a doctor’s aide in the outpatient department of the Zürich Eye Clinic and soon worked in her new husband’s office. They had two children, Gertrud (born 1910) and Rudolf Max (born 1913), who followed his father into brain research.

Focus on Research . Hess soon found that a successful practice interfered with his research. He had set up a laboratory to study hemodynamics as they related to blood viscosity and motor coordination, but had little time to spend there. So in 1912, even though it meant a significant cut in pay, Hess accepted a position as an assistant at the Institute of Physiology in Zürich, working under Professor Justus Gaule, a former student of Carl Ludwig. However, Gaule was ill at the time, and as a result Hess was pretty much left to his own devices.

Hess did not lack for research problems to solve. Primary among them was how vascular energy is conserved in circulation. Hess developed an idealized model of optimal vascular performance and then compared it with what he found in a living circulatory system. He presented this work for his Habilitationsschrift, a postdoctoral thesis, which was accepted by the medical faculty in 1913, and he was then promoted to privatdozent, or university professor.

World War I interrupted Hess’s research and laboratory teaching. Hess, along with everyone else fit for military service, was called to active duty in the Swiss army. As the war continued and the Allies were winning, he was able to return to laboratory research for a few months at a time. In particular, he worked as an assistant in the laboratory of Max Verworn in Bonn. A former student of Ernst Haeckel, Verworn had a lot of experience in general animal physiology, which was the sort of expertise that Hess was looking for. Hess was able to continue his research on hemodynamics with almost complete freedom, this time using dogs as an animal model.

Hess focused on understanding how bodies regulate regional blood flow, and how they adapt blood flow to the changing needs of different organs. At the time, scientists believed that the pulse in part was caused by arterial contractions. Hess investigated whether this notion of a “peripheral heart” was true by looking at a nonbranching section of the carotid artery. Unfortunately, after a year’s investigation, Hess only had negative results to report. After that year, Hess had to return both to Zürich and military service, and further research had to wait until after World War I was over.

In 1916 Gaule resigned from his position because of his continuing poor health. Hess was appointed to take his place temporarily until a replacement could be found. In 1917 he was named director of the Physiological Institute at the University of Zürich, though not without considerable opposition. As a newly appointed chief, Hess traveled to a number of British laboratories to learn how the English physiologists ran their programs, including the labs run by Ernest Starling, John Newport Lang, Frederick Hopkins, Henry Dale, and Charles Sherrington. Hess also attended a number of international conferences to learn all he could about cutting-edge research in physiology and general medicine so that he could bring this information back to his students.

Hemodynamics remained the focus subject in Hess’s institute. It expanded to include the autonomic properties of individual arteries, especially the reflex properties of the arterial rings. Experiments that stimulated arterial sections with salt solutions, adrenalin, acetylcholine, and other substances continued for years. Ultimately this research culminated in his 1930 monograph Die Regulierung des Blutkreislaufs, gleichzeitig ein Beitrag zur Physiologie des vegetativen Nervensystems(Regulation of the circulatory system). Hess noticed the close relationship between the circulatory and the respiratory systems and treated the regulation of the respiratory system in the same manner as he did the regulation of the circulatory system. Die Regulierung der Atmung, gleichzeitig ein Beitrag zur Physiologie des vegetativen Nervensystems (Regulation of respiration) followed in 1931.

Investigations into the Diencephalon . Hess’s shift to studying the regulatory functions of the diencephalon was actually an extension of his earlier interests. In all his earlier work, Hess was seeking to uncover the driving forces and the organizing principles of larger systems, seeking something like Walter B. Cannon’s notion of homeostasis. He also sought the meaning behind bodily activities, its “teleology,” a controversial stance at the time. Hess was bent on showing that nature optimized performance in context, an idea he first had in his childhood. These overarching goals led Hess to seek the site of the central operational elements, a place where somatomotor and autonomic inputs come together and are correlated with psychological functions. Building on the work of Johann Karplus, Alois Kreidl, and Philip Bard, which connected the sympathetic nervous system with the hypothalamus, Hess selected the diencephalon as the locus of his brain research, for it receives inputs from the visceral, gustatory, and olfactory systems and outputs to the pituitary gland. At the time, S. W. Ranson in Chicago did similar work and got results similar to Hess.

It became clear to Hess that before significant progress could be made, he would have to develop new experimental techniques to stimulate animals electrically while they were free to move about. In addition to working with extremely small electrodes, Hess established the minimum current required for an effect. These new techniques were extremely effective and Hess became quite well known for them.

In addition to new experimental techniques, Hess needed to be able to identify anatomical locations with great precision, which required careful microscopic study of serial histological sections. Hess’s experimental team— himself, two assistants (Ewald Weissschedel and Richard Jung), and one secretary/technician (Verena Bucher)— put together three atlases of photomicrographic reproductions of the serial sections cut perpendicular to one another, one for each dimension. By cross-referencing across the atlases, Hess could localize each area of stimulation and functional response precisely.

In 1927 Hess had introduced cinematography in recording, which allowed him to compare the details of experimental results across years. He also developed a filing system, in which data were arranged by functional symptoms. One could look up a symptom and retrieve the protocol, photomicrographic locations results, and the cinematographic documents. An immense collection of functional and morphological data concerning the thalamus, the hypothalamus, and nearby regions of the telencephalon and midbrain was amassed.

Hess published the technical side of this program in 1932 as the monograph Beiträge zur Physiologie des Hirnstammes. I. Die Methodik der lokalisierten Reizung und Ausschaltung subkortikaler Hirnabschnitte (The methodology of localized stimulation and destruction of subcortical brain areas). Neither this book, nor the second part, published as Beiträge zur Physiologie des Hirnstammes. II. Das Zwischenhirn und die Regulation von Kreislauf und Atmung, in 1938, became well known, largely because of World War II. In addition, only a small number of researchers worked in this area at the time, and Hess published in German, which was unpopular. Switzerland closed itself off to outsiders during the war, and all the type for these editions was destroyed in Leipzig during the war.

Hess continued these experiments, learning little by little how to localize function in the diencephalon. Only after he had collected a huge body of data could he see the functional patterns clearly. Using fine electrodes to stimulate or destroy specific areas of the brain in cats and dogs, Hess found that the seat of autonomous function lies at the base of the brain, in the medulla oblongata and the diencephalon, particularly that part of the interbrain known as the hypothalamus. During the experimental investigations of the diencephalon, he noted both regulatory representations, which control the activity of the internal organs in a coordinated fashion, and somatomotor effects. He focused on understanding the details of these latter symptoms and, in the process, demonstrated a relationship between supporting functions, automatic correcting movements, and the differentiated maintenance of tone in the skeletal musculature. Indeed, he mapped the control centers for each function to such a degree that he could induce the physical behavior pattern of a cat confronted by a dog simply by stimulating the proper points in the animal’s hypothalamus. Other studies concerned the control of parts of the forebrain (area orbitalis), in which Hess, together with Konrad Akert, uncovered the cortical representation of sight and the oral and pharyngeal regions.

This huge experimental effort was accomplished with only the help of Hess’s two assistants, a mechanic, a secretary/technician, and one graduate student. It led to the publication of almost three hundred original articles and two monographs published in 1948 and 1949, Die funktionelle Organisation des vegetativen Nervensystems, and Das Zwischenhirn: Syndrome, Lokalisationen, Funktionen, respectively. Hess’s work was well received, and in 1949, Hess was awarded the Nobel Prize in Physiology or Medicine for his “discovery of the functional organization of the diencephalon and its role in the coordination of the functions of the inner organs.” (He shared this award with Egaz Moniz, who had developed the frontal lobotomy as a therapeutic method for psychiatry.)

Other Experimental Results . Regulations required that Hess retire from his professorship and directorship of the Physiological Institute in 1951. Hess had the right to continue his research in other rooms placed at his disposal in the Physiological Institute, and so he continued his work, albeit on a smaller scale.

It was not lost on Hess that the stimulation experiments on the diencephalon occasionally gave rise to various modes of behavior, which suggested the possibility of localizing psychic functions in the brain. He focused his remaining years in research on the biological underpinnings of psychological phenomena. His approach and theories were eventually discussed in Hess’s final monographs: Psychologie in Biologischer Sicht (1962) and The Biology of Mind (1964).

Hess believed that sleep was an active state, not a passive one, as one might find with anesthesia. He concluded this based on careful observations of sleeping cats. He noticed that they experienced changes in their autonomic nervous system: slowed pulse, decreased blood pressure, contracted sphincter muscles, and dark adaptation of the retina. Electrical experimentation in the diencephalon revealed regions that, when stimulated, produced these active symptoms of sleep. The sleep region that Hess identified extended from the medial thalamus almost down to the caudate nucleus. His son, who introduced electroencephalography (EEG) to Switzerland, later demonstrated that Hess’s induction of sleep symptoms were accompanied by EEG patterns found in normal sleep. Hess’s work on the locus of sleep was controversial at the time, but his basic idea that there is a sleep-inducing projection system deep in the brain is now recognized as largely correct: the cortex receives ascending input from lower brainstem nuclei that modulates brain activity.

In addition to the defensive behaviors he could induce in cats with low-level brain stimulation, Hess also generated other sorts of complex behavioral responses. These included hunger and thirst behaviors, locomotion, cleaning behavior, as well as urination and defecation behaviors. These experiments raised the question of whether the responses were simple autonomic reflexes or required conscious motivational input. Hess was inclined toward the second possibility. It later became known that Hess was probably wrong in this assessment.

Finally, Hess, like many other neuroscientists of the time, was interested in the mind-brain problem. For Hess, psychic functions were an essential part of living organisms, especially for the higher forms of animal life. In particular, he believed that consciousness was a unique and unknown force in nature. These sorts of forces create psychic patterns, which are correlated with patterns found in the nervous system and brain. But beyond identifying correlations between conscious activity and the nervous system, Hess believed that there was little more that could be known about consciousness.

Hess’s Legacy . Hess’s work has helped bridge the gap that in many ways yawned between physiology and psychiatry. At the same time, Hess advanced hypotheses concerning how psychotropic drugs acted in the brain, the physiological foundations of psychosomatic phenomena, and the type-specific organization of the central nervous system.

Beyond the Nobel Prize, Hess received numerous honors during his life, including being named doctor honoris causa of the University of Bern (1934), the University of Geneva (1944), McGill University (1953), and the University of Freiburg im Breisgau (1959). He was the cofounder and chairman of the board of the Swiss High Altitude Research Laboratory in Jungfraujoch from 1931 to 1937. He was awarded the Marcel Benoist Prize in 1932. He was elected resident of the Sixteenth International Physiological Conference, which was held in Zürich in 1938. That same year, he received the Carl Ludwig Medal of the German Society of Circulation Research.

After retirement, Hess bought a vacation home in Ascona, which had a milder climate, and spent much of his time there, enjoying the weather and his fantastic gardens. Walter Hess died on 12 August 1973 in Locarno, Ascona, Switzerland.



“Eine mechanisch bedingte Gesetzmässigkeit im Bau des Blutgefässystems.” Wilhelm Roux Archive für ,Entwicklungsmechanik der Organismen 16 (1903): 632–641.

“Ein neuer Apparat zur Bestimmung der Viskosität des Blutes.” Berliner und Munchener Tierarztliche Wochenschrift 54 (1907): 1590–1591.

“Eine neue Untersuchungsmethode bei Doppelbildern.” Archiv Augenheilkd 62 (1908): 233–238.

“Das Prinzip des kleinsten Kraftverbrauches im Dienste haemodynamischer Forschung.” Archiv für Physiologie, no. 1/2 (1914): 1–62.

“Über dieWechselbeziehungen zwischen psychischen und vegetativen Funktionen.” Schweizer Archiv fur Neurologie und Psychiatrie 15 (1924): 260–277; 16 (1925): 36–55, 285–306.

“The Mechanism of Sleep.” American Journal of Physiology 90 (1929): 386–387.

Die Regulierung des Blutkreislaufs, gleichzeitig ein Beitrag zur Physiologie des vegetativen Nervensystems. Leipzig, Germany: Thieme, 1930.

Die Regulierung der Atmung, gleichzeitig ein Beitrag zur Physiologie des vegetativen Nervensystems. Leipzig, Germany: Thieme, 1931.

Beiträge zur Physiologie des Hirnstammes. I. Die Methodik der lokalisierten Reizung und Ausschaltung subkortikaler Hirnabschnitte. Leipzig, Germany: Thieme, 1932.

“Der Schlaf.” Klinische Wochenschrift 12 (1933): 129–134.

Beiträge zur Physiologie des Hirnstammes. II. Das Zwischenhirn und die Regulation von Kreislauf und Atmung. Leipzig, Germany: Thieme, 1938.

“Charakter der im Zwischenhirn ausgelösten Bewegungseffekte.” Pflugers Archiv fur die Gesamte Physiologie des Menschen und der Tiere 244 (1941): 767–786.

“Die Motorik als Organisationsproblem.” Biologisches Zentralblatt 61 (1941): 545–572.

“Biomotorik als Organisationsproblem.” Naturwissenschaften 30 (1942): 441–448, 537–541.

With M. Brügger. “Das subkortikale Zentrum der affektiven Abwehr.” Helvetica Physiologica et Pharmacologica Acta 1 (1943): 33–52.

“Hypothalamische Adynamie.” Helvetica Physiologica Acta 2 (1944): 137–147.

Die funktionelle Organisation des vegetativen Nervensystems. Basel, Switzerland: Schwabe, 1948.

Das Zwischenhirn: Syndrome, Lokalisationen, Funktionen. Basel, Switzerland: Schwabe, 1949; 2nd ed., 1954.

“Funktion und nervöse Regulation der innern Organe.” Vierteljahrschr Naturforsch Ges Zürich 95 (1950): 249–264. Diencephalon. Autonomic and Extrapyramidal Functions. New York: Grune and Stratton, 1954.

Hypothalamus and Thalamus: Documentary Pictures. Hypothalamus und Thalamus: Experimental-Dokumente. With German and English text. Stuttgart, Germany: Thieme, 1956; 2nd ed., 1969.

Psychologie in Biologischer Sicht. Stuttgart, Germany: Thieme, 1962; 2nd ed., 1968.

“From Medical Practice to Theoretical Medicine. An Autobiographic Sketch.” Perspectives in Biology and Medicine 6 (1963): 400–423.

The Biology of Mind. Chicago: University of Chicago Press, 1964.

“Walter Rudolf Hess.” Nobel Lectures, Physiology or Medicine, 1942–1962. Amsterdam: Elsevier Publishing, 1964.

“Causality, Consciousness and Cerebral Organization.” Science 158 (1967): 1279–1283.


Akert, Konrad. “Walter Rudolf Hess (1881–1973) and His Contribution to Neuroscience.” Journal of the History of the Neurosciences 8, no. 3 (1999): 248–263.

Huber, A. “Walter Rudolf Hess as an Ophthalmologist.” Gesnerus 39, no. 2 (1982): 287–293. In German.

Jung, Richard. “Walter R. Hess (1881–1973).” Review of Physiology, Biochemistry, and Pharmacology 88 (1981): 1–21. In German.

Waser, Peter. G. “Walter Rudolf Hess: His Life and Activities at the University of Zürich Medical School Centennial Celebration of His Birth: 14 March 1981.” Gesnerus 39, no. 2 (1982): 279–286. In German.

Valerie Gray Hardcastle

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Walter Rudolf Hess

Walter Rudolf Hess

A Swiss neurophysiologist, Walter Rudolf Hess (1881-1973) won the 1949 Nobel Prize for Physiology or Medicine (with Antonio Egas Moniz) for discovering the role played by certain parts of the brain in coordinating the functions of internal organs.

The son of Professor Clemenz Hess, Walter Rudolf Hess was born at Frauenfeld, Switzerland, on March 17, 1881. In 1900 he became a medical student at the University of Lausanne, and after more study in Switzerland and Germany, he graduated from the University of Zurich in 1906. He became a practicing ophthalmologist, but in 1912 he turned to physiology. In 1917 Hess was appointed professor of physiology and director of the Institute of Physiology at the University of Zurich.

The Experiments

Hess soon became interested in the study of the autonomic nervous system, the nerves that originate at the base of the brain and extend throughout the spinal cord. These nerves control such functions as digestion and also trigger the response of organs to such stimuli as stress. In 1925 Hess began work on the influence of the diencephalon (interbrain)—especially the hypothalamus—in relation to the regulation of involuntary activities that enable the individual to function as an integrated organism.

At the time, it was known that the autonomic nervous system was divided into the sympathetic and the parasympathetic and that these two divisions were in general mutually antagonistic. Involuntary muscles and glands were supplied by two types of fibers, one excitatory and the other inhibitory. But much less was known about the action of the central origins of the autonomic nervous system in the brain, mainly in the hypothalamus. A few scientists had observed the reactions in animals following stimulation of poorly localized areas of the hypothalamus. It thus came to be realized that the hypothalamus, through the autonomic nervous system, controlled the automatic functions of the body, such as the blood supply to muscles and organs, mechanism of heat regulation, activity of the gastrointestinal tract, and the regulation of basal metabolism, of the sugar content of the blood, and of blood pressure. But to a large extent, the exact areas responsible for such functions had never been precisely localized.

Hess developed his own brilliant technique for the investigation of such problems. Others had used needle electrodes implanted in the hypothalamus to pass an electric current to a desired area, but locations were generally not precise. Hess implanted his electrodes accurately under general anesthesia. The needle electrode, insulated except at the very tip, was connected to a frame fixed to the skull. When the animal had recovered from the operation, a very weak current was passed through the electrode, and the animal's reaction, giving the result of stimulation at the site of the tip of the electrode, was very carefully recorded. After repeated observations of this type, the minute area around the tip of the electrode was coagulated by a current, and the animal's reaction was again recorded. At autopsy, serial sections were made of the animal's brain in order to identify the exact situation at the tip of the electrode. The correlation of these clinical and anatomical findings involved a very careful recording technique. Hess's experiments were carried out on a scale never previously attempted.

Hess proved conclusively that bodily functions, triggered by the sympathetic division of the autonomic nervous system, are related to the posterior and middle parts of the hypothalamus. Stimulation of a certain area of the hypothalamus of a cat produces all the symptoms of rage. Stimulation of another defined area produces parasympathetic, not sympathetic, effects; the cat relaxes and falls asleep. By these methods Hess mapped out the influence of the hypothalamus, and for his work he was awarded a Nobel Prize, with Antonio Egas Moniz, in 1949.

After his official retirement in 1951, Hess continued to work in the Institute of Physiology. He was already the author of several books, and in 1956 he published an atlas of sections of the hypothalamus and the thalamus. In 1962 he published a work that related his research to psychosomatic phenomena and the behavior pattern of the individual (2d ed., 1968). Hess received many honors, including honorary degrees from four universities and in 1971, the Johannes Müller Medal. He died in Locarno, Switzerland, on Aug. 12, 1973.

Further Reading

There is a biography of Hess in Nobel Lectures, Physiology or Medicine, 1942—1962 (1964), which also includes his Nobel Lecture. For the physiology of the autonomic system and hypothalamus see J. F. Fulton, Physiology of the Nervous System (3d ed. 1949). For the historical aspects see J. Beattie in W. E. LeGros Clark and others, The Hypothalamus (1938). □

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Hess, Walter Rudolf

Walter Rudolf Hess, 1881–1973, Swiss physiologist. For his work on the control of organs by certain areas of the brain he shared with Egas Moniz the 1949 Nobel Prize in Physiology or Medicine. He was (1917–51) professor and director of the physiology institute at the Univ. of Zürich.

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