Advances in Understanding the Nervous System | Research & Encyclopedia Articles

Neurology, the study of the brain along with the body's nervous system, had little structure in the medical community of late-Medieval and Renaissance Europe. The renewed intellectual enthusiasm of the Renaissance brought about an appreciation for classical study, and with it advances in the knowledge of the anatomy of the human brain. Much of the period, however, was devoted not to seeking practical medical knowledge about the nervous system, but to pondering the philosophies of its nature. Occasionally, empirics or quacks filled the void, performing surgeries on the scalp, administering drugs or herbs, or chanting for the benefit of a patient with headache, neuromuscular difficulty, or mental illness. By the end of the seventeenth century, however, the scientific and Hippocratic methods, based on direct observation and experimentation, were laying the foundation for the future study of neurology.

Medieval understanding of the nervous system was basically limited to observations of animal anatomy, tempered by philosophies prevailing since antiquity. The influence of Greek physician Galen of Pergamum (c. 130-c. 200) on medical theory and practice was dominant in Europe throughout the Middle Ages and into the Renaissance. Galen thought that the best physicians were also philosophers, and that philosophy promoted medicine. Galenic tradition held that illness was a result of an imbalance of body fluids, or humors. While dissecting calves, Galen noticed a network of nerves and vessels at the base of the calf brain that he mistakenly assumed also existed in humans. Galen labeled this area the rete mirabile, and stated that this was the site where vital life spirits were transformed into man's animal spirits. After the advent of Christianity, these spirits were unified into the concept of a Christian soul, and physicians debated its base in the human body, presumably the heart or the brain.

By the mid-1600s scientists considered the structure and philosophy of the brain based upon observations on humans. English physician and anatomist Thomas Willis (1621-1675) was the first to name the fledgling science of neurology. Willis was professor of philosophy at Oxford University, and he built one of the largest and best-known medical practices of his day. Willis belonged to the new school of iatrochemists, who believed that animal physiological activity could best be explained by chemical interactions. By removing the brain from the cranium,Willis was able to clearly visualize its structures. Willis accurately described the hexagonal network of arteries (the circle of Willis) at the base of the brain that is responsible for ensuring the brain's blood supply as the body's highest priority. He identified the eleventh cranial nerve (the spinal accessory nerve) responsible for motor stimulation of major neck muscles. Willis also distinguished gray matter from white matter, and ventured that the gray matter held the animal spirits, while the white matter distributed the spirits throughout the body, giving rise to movement and sensation. Willis rejected the Galenic tradition of the spirits as fluids, however, when he noticed the speed with which sensations and muscular actions occur. Willis likened the spirits to rays of light, quickly filling the passages of nerves, thus resembling an elementary concept of nerve conduction. Along with French philosopher René Descartes (1594-1650), Willis was one of the last of the animal spirit theorists. Still, he accepted the idea of a soul unique to man, possessing the ability to reason. In 1664 Willis published Cerebri Anatome, the most accurate and complete account of the nervous system yet published, containing detailed illustrations by Christopher Wren (1632-1723).

In France Willis's work was carried on by the French physician Raymond Vieussens (1641-1715). Vieussens held the post of chief surgeon at Hotel Dieu at St. Eloi (near Montpellier) for most of his adult life. Inspired by both Descartes's mechanistic and the iatrochemical philosophies, Vieussens studied the white matter of the brain by tracing the path of its fibers. Because of his tendency to explain his observations with fantastic physiological explanations, Vieussens sometimes drew harsh criticism from the faculty of medicine at Montpellier University. Vieussens had an advocate in the Marquis de Castries, who shielded him from attacks of the faculty and probably provided financial patronage, allowing Vieussens to continue his clinical and experimental work in relative peace. In 1685 Vieussens published the well-received Neurographica Universalis, detailing the central and peripheral nervous systems.

Descartes, a French mathematician and philosopher, sought to separate the rational soul from the physiology of the body. Descartes's concept of the body was that of an intricate machine. Descartes belonged to the school of iatrophysics, in which the workings of the animal body were explained purely on mechanical grounds. The rational soul, according to Descartes, interacted with the body via the pineal gland of the brain. The animal spirits flowed from the ventricles of the brain, carrying instructions to the muscles that could be over-ruled or modified by the rational soul. Descartes saw the rational soul as the seat of wisdom, and the pineal area of the brain as the center of all sensory input. Descartes also is credited with the founding of reflex theory. Descartes articulated a mechanism for an automatic reaction, beginning with an external motion displacing the peripheral ends of nerves. The central ends of the nerves were, in turn, displaced, which allowed the flow of animal spirits from the center of the nerves to the surrounding appropriate areas, creating an involuntary reaction. Although the mechanism for a reflex action advanced by Descartes was faulty, the fact that the reflex action was a predicted automatic response to a stimulus remains.

During the Renaissance progress was much slower in the practice of medicine than in its science. Typically, the medicine of the Renaissance benefited the doctor more than his patient, and many physicians occupied much of their time debating the numerous prevailing philosophies of the workings of the body, leaving the actual care of the sick to barbers, empirics, and folk healers. In no area of medicine did so many philosophies exist ready for discussion than the workings of the brain and nervous system.

Although Descartes was proved wrong in his belief that the pineal gland was the focus of all sensory input, his belief in the rational soul did not find disfavor with many religious leaders of the day. Christianity was consistent with a separate soul that departed the body after death, one that could be held accountable for the body's earthly actions. The Cartesian dualism of a separate body and rational soul allowed Descartes to justify the strident religious demands of the time (Descartes was aware of his contemporary, Galileo, and his persecution during the Inquisition) with his belief in the mechanical nature of the workings of the human body. Descartes's dualism was outlined in his De Homine (On Man), published posthumously in 1662.

The urge to apply philosophical principles to the practice of medicine continued throughout the Renaissance. This led to variations on systems to explain disease, sometimes with unusual methods of treatment. Friedrich Hoffmann (1660-1742), a chemist and physicist, envisionedthe body as composed of individual fibers. The fibers dilated and contracted, according to Hoffmann, in response to a "nervous ether" substance in the brain, which traveled to all parts of the body via the spinal cord. The contractile property was tonus, and every change in tonus was thought to bring about a change in health. Hoffman attempted to regulate tonus with several drugs he labeled "tonics." Tonic became a catch-all term for questionable remedies up until the twentieth century.

Beginning in about 1650 several factors set the stage to nurture the legitimate, new science of neurology. The renewed interest in the classics brought about by Renaissance thinking reintroduced the Hippocratic method of careful observation of patients and their symptoms. Descartes demystified the human body with his mechanical conception of human physiology. When opposition to human dissection evaporated, Andreas Vesalius (1514-1565) saw first-hand the structure of the human body, and pioneered the study of modern anatomy and physiology. Removed from the hands of barber-surgeons, anatomy evolved to an exacting science viewed with respect among physicians and medical academics. With the invention of the microscope, nerve cells were first visualized in the early 1700s, and nerve cell function studies were initiated. Eventually, eighteenth-century scientists contemplated the spark of life itself, and debated its natural, spiritual, or electrical origin in the human brain.

Carter, R. B. Descartes' Medical Philosophy: The Organic Solution to the Mind-Body Problem. Baltimore: Johns Hopkins University Press, 1983.

Finger, S. Origins of Neuroscience: A History of Explorations into Brain Function. New York: Oxford University Press, 1994.

Spillane, J. The Doctrine of the Nerves. London: Oxford University Press, 1981.

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