Willis Identifies the Basal Ganglia

Locale Oxford and London, England

Date 1664

Thomas Willis published his masterpiece, Cerebri anatome, which included groundbreaking descriptions, illustrations, and analyses of several important brain structures, especially at the base of the brain. Willis thereby became the central figure in the rapidly advancing brain studies of the seventeenth century.

Key Figures

• Thomas Willis (1621-1675), English physician, anatomist, physiologist, and chemist
• Richard Lower (1631-1691), English physician, anatomist, and physiologist
• Sir Thomas Millington (1628-1704), English physician and physiologist
• Sir Christopher Wren (1632-1723), English architect, physiologist, and illustrator
• Raymond Vieussens (1635-1715), French physician and surgeon
• Nicolaus Steno (1638-1686), Danish physician, anatomist, and Roman Catholic priest
• René Descartes (1596-1650), French philosopher, mathematician, and physiologist
• Gerardus Leonardus Blasius (1626?-1692), Dutch physician and anatomist
• Johann Jacob Wepfer (1620-1695), Swiss physician and anatomist

Summary of Event

When Thomas Willis published Cerebri anatome (1664; The Anatomy of the Brain , 1681), he effectively founded the modern neurosciences, particularly neurology and neuroanatomy. With only a few minor exceptions, knowledge of the brain and its functions had not changed much from Galen in the second century until early in the seventeenth century, and most of that “knowledge” was wrong. Scientists did not even agree that the brain was the organ of thought, and many assigned that role to the heart. The credit for the quantum leap forward represented by Cerebri anatome does not belong to Willis alone, however: Even though his is the only name that appears on the title page, Cerebri anatome was actually a collaborative effort of four University of Oxford colleagues, Richard Lower as dissector, Willis and Thomas Millington as physiologists, and Christopher Wren as illustrator.

Cerebri anatome is best known for its presentation of findings about the cerebral arterial circle, the pentagonal confluence of the two posterior cerebral arteries arising from the basilar artery, the two posterior communicating arteries, the two middle cerebral arteries, the two internal carotid arteries, the two anterior cerebral arteries, and the anterior communicating artery. Many anatomists, notably Johann Jacob Wepfer in Observationes anatomicae (1658), described the cerebral arterial circle before Willis, but they did not understand its purpose. It is commonly known as the “circle of Willis,” because he discovered that its physiological function is to protect the brain from ischemia, or loss of blood supply.

The circle of Willis works through anastomosis, a process in which several arteries are so closely connected that they share their contents. If any of the three feeder arteries, the basilar or either of the two internal carotids, are blocked or cut, then the others instantly redistribute the blood so that the flow to the brain is not interrupted through the pairs of posterior, middle, and anterior cerebral arteries. This prevents brain damage from local anemia.

Before the eighteenth century, the only significant advocates of brain function localization were Willis, René Descartes, and Nicolaus Steno . Willis verified that the cerebellum controlled the vital functions and believed that the cerebrum was the organ of thought. Descartes performed experiments on the locus of sight and argued that the pineal gland was the seat of the soul and hence of thought. Most of Willis’s analyses of Lower’s brain dissections were aimed at discovering localized functions or assigning specific physiological tasks to specific parts or areas of the brain. Above all, he was looking for the seat of Aristotle’s sensus communis (common sense), which was supposed to mediate among the data gathered by the five physical senses. Galen had believed that the ventricles were the organs of thought and that the ventricular fluid was the means by which the brain transmitted information. Willis abandoned that notion and correctly identified the cortex as the thinking part of the brain, but he incorrectly decided that the common sense was located in the corpus striatum (striped body).

The corpus striatum is the main component of the basal ganglia, which consist of all the interconnected gray matter and nerve structures that lie in two divisions deep in the center of the brain, beneath the cortex and on either side of the thalamus. Besides the physiology of the cerebral arterial circle, Willis’s most important contribution to neuroscience was his work on the basal ganglia. “Ganglia” is the plural of “ganglion,” which is any group or knot of nerve cells. Because of their core location, Willis believed that the basal ganglia served both the motor and the sensory functions. This guess was essentially correct, but scientists would be unable to verify it or to sort out the subtleties of the situation until the twentieth century.

Although Willis was convinced that each part of the brain had a specific function, he could not prove it. Steno agreed with Willis about cerebral localization in principle but attacked some of Willis’s physiological conclusions on the grounds that Willis showed insufficient anatomical evidence for them. Steno strongly disagreed with Willis that the basal ganglia housed the common sense. He urged scientists to limit their speculation about localized brain function until they understood brain anatomy better.

Besides Willis, the most important brain researchers of the seventeenth century were Gerardus Leonardus Blasius, Descartes, Steno, and Raymond Vieussens. Together, by the end of the seventeenth century, they had discovered or described most of the gross or macroscopic anatomical structures of the brain. Blasius discovered the arachnoid, the middle of the three membranes that enclose the brain. In the dura mater, the outer of these three membranes, Willis discovered fibers crossing the superior sagittal sinus, a long duct or groove along the midline of the cranium running from the front, across the top, to the back of the brain. These fibers are now called “Willis’s cords.”

Among seventeenth century books on neuroanatomy, only Cerebri anatome is more important than Vieussens’s major work, Neurographia universalis (1684; general neurography). Vieussens provided the earliest precise descriptions and illustrations of many small structures in the brain, and three are named for him: “Vieussens’s centrum,” or centrum ovale, the white oval core of each brain hemisphere; “Vieussens’s valve,” a sheet of thin white tissue; and “Vieussens’s ventricle,” a fluid-filled space.

Much seventeenth century brain research, including Willis’, was prompted by the mind/body problem formulated by Descartes in Discours de la Méthode (1637; Discourse on Method , 1649) and Meditationes de prima philosophie (1641; Meditations on First Philosophy , 1680). Cartesian dualism claims that the self definitely exists as a thinking thing, but that the precise nature of the connection of this mind or soul with the physical world, including its own body, is difficult to ascertain. These early neurologists were seeking religious and philosophical knowledge of the soul as much as biomedical knowledge of the brain. Willis was a very religious man, and made every effort to connect his physiological and anatomical work with his conception of the brain as “the chapel of the deity” so that the Church of England could use his science in its theological disputes with other churches.

Significance

Cerebri anatome was the most important book on brain anatomy and physiology until German anatomist and physician Samuel Thomas Soemmering improved Willis’s description of the cranial nerves in 1778 and Scottish anatomist and physician Alexander Monro, Secundus, published Observations on the Structure and Functions of the Nervous System (1783). The fact that Cerebri anatome remained the dominant influence in neurology and neuroanatomy for more than one hundred years is testimony not only to the precision of Lower’s dissections and Willis’s observations, the depth of their intelligence, and the thoroughness of their investigations, but also to the production values of the book itself. It is a beautifully executed volume, with Wren’s illustrations standing out as true works of art.

The neuroanatomical and neurophysiological discoveries of Willis and his contemporaries created the modern science of the nervous system and laid the groundwork for disciplines as diverse as neurosurgery and psychiatry.

Bibliography

Brazier, Mary Agnes Burniston. A History of Neurophysiology in the Seventeenth and Eighteenth Centuries: From Concept to Experiment. New York: Raven Press, 1984. The standard scholarly work in this field.

Clarke, Edwin, and Kenneth Dewhurst. An Illustrated History of Brain Function. Berkeley: University of California Press, 1974. Beautifully produced, accessible, and authoritative.

Coulter, Harris L. The Origins of Modern Western Medicine: J.B. van Helmont to Claude Bernard. Vol. 2 in Divided Legacy: A History of the Schism in Medical Thought. Berkeley, Calif.: North Atlantic Books, 2000. The second chapter, “Seventeenth-Century Rationalism,” explores the rivalry between iatrochemisty and iatromechanics.

Finger, Stanley. Origins of Neuroscience: A History of Explorations into Brain Function. New York: Oxford University Press, 1994. An illustrated chronological survey of the persons and concepts that have shaped neuroscience.

Frank, Robert Gregg. Harvey and the Oxford Physiologists: A Study of Scientific Ideas. Berkeley: University of California Press, 1980. This standard scholarly work sets Willis’s research on blood, fermentation, the brain, muscles, respiration, and physiological chemistry in its historical and interpersonal context.

Meyer, Alfred. Historical Aspects of Cerebral Anatomy. London: Oxford University Press, 1971. Written by a neuropathologist and organized by specific regions of the brain, this book is perhaps too technical for a general readership. Willis is among the most often mentioned names.

Rocca, Julius. Galen on the Brain: Anatomical Knowledge and Physiological Speculation in the Second Century A.D. New York: E. J. Brill, 2003. Excellent background information on the state of neurology and neuroanatomy before Willis.

Zimmer, Carl. Soul Made Flesh: The Discovery of the Brain and How It Changed the World. New York: Free Press, 2004. The central character in this well-told drama is Willis, the turning point is the seventeenth century, and the main locale is Oxford. Accordingly, the subtitle of the British edition (London: Heinemann, 2004) is Thomas Willis, The English Civil War, and the Mapping of the Mind.