Careful neurologists search for something in their library or file cabinet every day. The more compulsive among us will, on occasion, find our notes from a particularly important lecture that we attended 20 or even 30 years ago. Accidental historians sometimes come across lecture notes that hundreds of years old, yet still can capture the neurological imagination. One such lecture was delivered 339 years ago.
The estimable Neils Stensen was born in Copenhagen in 1638 into a family of goldsmiths and jewelers. He worked in his father's workshop as a child, acquiring a fine dexterity in the process. His school days were disrupted by a visitation of the plague, which killed half of his classmates. At age 18, he began the study of medicine at the University of Copenhagen. His studies were again interrupted, this time by a war with Sweden in which Copenhagen was attacked.
Stensen began anatomical research in his native city, but soon left Denmark to continue his anatomical investigations in Amsterdam. There he demonstrated the presence of the parotid duct, now known eponymously as Stensen's duct. He published his finding under his Latinized name Nicolaus Steno, but his professor Gerhard Bläes claimed the discovery as his own. The priority dispute drove Stensen from Amsterdam to Leiden, where he came under the influence of Franciscus Sylvius. In Leiden, he learned the anatomy and Galenic physiology of the brain.
NEUROANATOMY: FORWARD THINKING
In 1664, after a brief sojourn in Copenhagen, Stensen joined his Dutch friend Jan Swammerdam at the home of the French royal chamberlain and librarian Melchisedec Thévenot. It was a fortuitous visit. Thévenot had collected around himself a sparkling intellectual and scientific circle, which in 1666 formed the nucleus of the Académie Royal des Sciences. It was at a 1665 meeting of the Thévenot circle that Stensen gave his amazing lecture, a lecture that moved neuroanatomy forward like few other single lectures before or since.
Stensen's lecture was published under the title “Discours de Monsieur Steno sur l'anatomie du cerveau.” You can read an English translation in Clark and O'Malley's The Human Brain and Spinal Cord (Norman Publishing, 1996). It contains both a more or less explicit rejection of Galenic orthodoxy and an original observation about the anatomy of the white matter. Stensen criticized the conventional thinking of the day, pointing out that it is not possible to discover anything new if you believe that everything important has already been discovered. He pointed to the slavish adherence to the ancients, by whom he meant Galen. As a corollary, Stensen asserted that following only the methods used by your predecessors is a good way to limit the scope of things you can discover. It follows that a critical aspect of science is the development and refinement of new methods of study. It helps if you understand the many things that you do not know about your subject of study.
Stensen advocated a comparative study of the brains of different animals, asserting that their anatomy and physiology will be similar enough to learn about general scientific principles. For example, he proposed dissecting the brain from the cortical surface though the basal regions, following the white matter tracts from the cortical surface to their entry into the brain or spinal cord. Stensen assumed a functional continuity between the cortex and the spinal cord, which was not to be completely accepted for more than 200 years.
ACCOMPLISHED IN MANY FIELDS
Stensen packed a lot of living into his 48 years. In mineralogy, he proposed that the angle between the surfaces of a crystal is constant, which is now known as Stensen's law of crystallography. In natural science, he asserted that fossilized shark's teeth are actual teeth of ancient sharks, and that items in lower strata are older than those in higher strata. These observations might be considered the beginning of systematic paleontology. In the final decade of his life, Stensen completely abandoned his scientific studies, converted from Lutheranism to Roman Catholicism, and joined the church hierarchy. He was pious and ascetic, reforming his dioceses and attending to the sick and impoverished. He is revered in the Danish Catholic Church, and was beatified in 1988. Who knows, he may become the only great neuroanatomist to be a recognized Catholic saint.
Stensen's indirectly criticized Thomas Willis for making unsupported assertions about the basal ganglia, an error that Willis admitted. His admonition against slicing the brain for anatomical study held force for more than 100 years. Not many lectures have such an impact. Think about that the next time you attend a great lecture, and consider whether what you are hearing will match Steno.