In a series of lectures at Yale University, Charles Scott Sherrington clarified the role of the nervous system in molding adaptive hierarchies of reflexes into purposeful behavior.
Charles Scott Sherrington’s publication of The Integrative Action of the Nervous System (1906)
Early ideas about reflexes were speculative, not experimental, and appeared as ancient philosophers and physicians tried to comprehend puzzling observations about humans in health and disease. They believed that injured organs affected other organs even though no connection was seen between them. Aristotle, for example, noted that sometimes there were “motions of the heart and of the penis; for often upon an image arising and without express mandate of the intellect these parts are moved.” Involuntary or sympathetic motions were distinguished from nonvoluntary motions such as falling asleep, waking up, and respiration, in which imagination and desire play no role. Heartbeats, on the other hand, were understood to be both sympathetic and nonvoluntary. One did not have to will one’s heart to beat, but passions affected the rate of the heartbeat. Galen, a Greek physician, kept Aristotle’s distinctions and added other examples, such as the contraction of pupils when exposed to light, a response independent of the will. The regularity of such responses to stimuli puzzled ancient philosophers.
René Descartes inherited these ideas about sympathy when he developed his mechanical model of the animal body in the seventeenth century. In Traité de l’homme (1664; Treatise of Man, 1972),
Stephen Hales
Most of the major work leading to the modern understanding of the reflex followed from the Bell-Magendie law,
As important as these physiological discoveries were, the microanatomy of the reflex remained hidden. Progress was impossible until theoretical advances such as cell theory and technological advances such as staining techniques and oil-immersion lens microscopes were applied to neuroanatomy. Camillo Golgi and Santiago Ramón y Cajal used these new technologies to uncover the details of nerve cells, but they interpreted their results differently. Golgi claimed that nerves form a patterned network and that nerve impulses spread wherever neural nodes overlap (reticularist model). Ramón y Cajal, on the other hand, saw individual nerves as approaching each other but never touching (neurone model). Both models had strengths and weaknesses that complemented each other: The neurone model offered clear pathways but no communication between nerves; the network offered communication but no clear pathways.
Charles Scott Sherrington.
By the 1890’s, physiological and anatomical pieces to the reflex puzzle abounded, but no one had crafted a synoptic vision to place them into a coherent whole. Sherrington confronted this confusion when he began his work. He was well prepared for this task. He was educated as a physician, trained in physiology under Sir Michael Foster, and exposed to the best European physiologists. Despite his preparation, the enormity of the task astounded him. He eventually delineated the sensorimotor pathways of the macaque monkey. Foster had told his students that the nervous system functions as a unity, not as individual pieces, and Sherrington was determined to discover that unity.
Yale University invited Sherrington to present his research in its prestigious Silliman Lecture series in the spring of 1904, and this opportunity allowed him to synthesize his ideas on the unity of nervous action. The lectures were published two years later in The Integrative Action of the Nervous System. Sherrington’s thesis in this work was that “the nervous synthesis of an individual from what without it were a mere aggregation of commensal organs resolves itself into co-ordination by reflex action.” In other words, how are distinct activities such as scratching, blinking, and maintaining posture coordinated with other activities such as breathing and walking to compose ultimately an individual animal?
Sherrington stated this issue more clearly in a 1933 lecture at Cambridge University, “The Brain and Its Mechanisms”: “How a limited set of agents of the outside world working through the nerve and brain of the animal can produce from its muscles the thousand and one dexterous acts of normal behaviour is itself a problem.” His answer began with an analysis of the three functions of the nerve cell: to support its own life, to communicate with other cells, and to integrate sensorimotor activity into complex behavior. Only nerve cells carry on the last of these functions, so the nervous system regulates the interplay between any animal and its environment. Reflexes, Sherrington argued, are the most basic units of sensorimotor activity, and it is their coordination into purposeful behavior that defines the integrative action of the nervous system. Sherrington’s simplicity of experimental technique and clarity of argument ordered reflexology’s pieces into a coherent pattern.
Sherrington introduced one of the most basic concepts in neurology: the synapse.
Reflexes, Sherrington asserted, play an evolutionary, or adaptive, role. In terms he coined himself, he claimed that proprioceptive reflexes, which give an animal a sense of place, and nociceptive reflexes, which give a sense of pain, are necessary for the survival of any individual. Despite the progress represented by The Integrative Action of the Nervous System, Sherrington acknowledged that he had hardly begun to understand the complexities of human behavior.
One reviewer of The Integrative Action of the Nervous System likened Sherrington to Sir Isaac Newton; a former student of Sherrington compared him to William Harvey. Sherrington’s work was praised not only because it cleared up many neuroanatomical and neurophysiological questions but also because it raised those sciences to new levels and suggested new directions for research.
Sherrington’s endorsement of Ramón y Cajal’s neurone theory and the postulation of the synapse stimulated his students to discover unsuspected chemical and electrical activities in the transmission of the nerve impulse across synapses. The newer vacuum tube technology allowed Edgar Douglas Adrian, along with others, to amplify minute electrical charge variations in nerves. This tool enabled researchers to explore afferent nerve impulses (impulses conveyed toward the central nervous system) and to discover the electrical coding of nerve signals. Sir Henry Hallet Dale, who later became director of the Wellcome Physiological Research Laboratory, pioneered with others the recognition of acetylcholine as a neurotransmitter. Adrian’s work led to Hans Berger’s development of the electroencephalogram (EEG) in 1929; Dale’s work helped stimulate the rapidly expanding field of neurochemistry.
The Integrative Action of the Nervous System enhanced Sherrington’s already high reputation and helped create the Sherrington School of Physiology. From all over the world, students flocked to the University of Oxford to work with Sherrington and then returned to their home institutions to continue the research they had begun with him. Several Nobel laureates were nurtured under Sherrington’s tutelage.
Sherrington’s interpretation of reflex action raised old questions again about the relationship of philosophy and theology to the scientific understanding of human behavior. Sherrington often said that after twenty-five hundred years of examining the physiological foundation of behavior, researchers were still in basically the same position as Aristotle. Sherrington and several of his contemporaries had been trained in a materialist physiology that viewed advances in reflexology as pushing back the domain of vitalist or idealist doctrines. As he matured, however, Sherrington moved from materialistic monism to a body/mind dualism. He accepted the reality of an independent mind, for although he could not explain it physiologically, neither could he explain the complexity of human behavior—as opposed to animal behavior—only in terms of reflexes. In later essays, Sherrington expressed fear concerning the political and social ramifications of a too-hasty solution to these ancient problems. He deeply influenced John Carew Eccles, one of his students, who continued to reflect on these issues until his death in 1997.
Certainly not all physiologists shared Sherrington’s views. Ivan Petrovich Pavlov, Sherrington’s contemporary, remained staunchly materialistic. Pavlov believed that all behavior, including human behavior, could be reduced to reflexes. He concluded from his experiments on dogs that learning itself is a variety of sensorimotor activity. Surprised by Sherrington’s dualism in “The Brain and Its Mechanisms,” he wondered aloud to colleagues if Sherrington had become ill or senile.
When in the 1930’s Sherrington looked back on his work, he admitted candidly that his reflex studies were limited and had served their purpose. Since that time, neuroscience has bloomed luxuriantly in fields with applications Sherrington could never have imagined, yet hardly any of its aspects do not owe something of their roots to The Integrative Action of the Nervous System.
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Clarke, Edwin, and L. S. Jacyna. Nineteenth-Century Origins of Neuroscientific Concepts. Berkeley: University of California Press, 1987. Modern scholarship places Sherrington’s achievement in the context of nineteenth century neurology. -
Eccles, John C. The Human Mystery. New York: Springer-Verlag, 1979. Presents Eccles’s Gifford Lectures at the University of Edinburgh, 1977-1978. Reflects on themes Sherrington presented in his Gifford Lectures of 1937-1938, later published as Man on His Nature (1941). -
Eccles, John C., and William C. Gibson. Sherrington: His Life and Thought. New York: Springer-Verlag, 1979. Eccles, a former student, and Gibson, a historian of science, examine Sherrington’s scientific work after 1906 and his philosophical essays written in later life. Memoirs and interviews bring to life what it was like to work with Sherrington. -
Finger, Stanley. Minds Behind the Brain: A History of the Pioneers and Their Discoveries. New York: Oxford University Press, 1999. Relates the history of humankind’s understanding of the brain through the work of important individuals who have influenced progress in this area. Chapter 14 is devoted to discussion of Sherrington’s work on the nervous system. -
Granit, Ragnar. Charles Scott Sherrington: An Appraisal. London: Thomas Nelson, 1966. Memoir by one of Sherrington’s students takes a relatively personal approach to discussion of The Integrative Action of the Nervous System. -
Jeannerod, Marc. The Brain Machine: The Development of Neurophysiological Thought. Translated by David Urion. Cambridge, Mass.: Harvard University Press, 1985. A frankly materialistic historical interpretation of neurophysiology that contrasts with Sherrington’s view. -
Liddell, Edward George Tandy. The Discovery of Reflexes. Oxford, England: Clarendon Press, 1960. One of the earliest scholarly historical accounts of the background of Sherrington’s achievement, written by a member of his laboratory. Covers only the years up to publication of The Integrative Action of the Nervous System. -
Ramón y Cajal, Santiago. Recollections of My Life. Translated by E. Home Craigie with Juan Cano. Cambridge, Mass.: MIT Press, 1989. Widely considered to be a particularly fine example of scientific autobiography. Original Spanish edition was reprinted often in Madrid between 1901 and 1917; first English edition appeared in 1937. -
Sherrington, Sir Charles Scott. The Integrative Action of the Nervous System. 1906. Reprint. New York: Ayer, 1973. Contains the complete text of the Silliman Lectures, expanded with charts, experimental protocols, and an immense bibliography. -
_______. Man on His Nature. 1941. Reprint. New York: Cambridge University Press, 1975. Contains the text of the Gifford Lectures presented at the University of Edinburgh, 1937-1938. Depicts a mature Sherrington reflecting on his life’s work and its significance. -
Swazey, Judith P. Reflexes and Motor Integration: Sherrington’s Concept of Integrative Action. Cambridge, Mass.: Harvard University Press, 1969. Excellent scholarly examination of Sherrington’s work, especially The Integrative Action of the Nervous System. Includes lengthy discussion of the background of his work, clear diagrams (some from Sherrington), and abundant documentation.
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