Ramón Y Cajal, Santiago (1852-1934)

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RAMÓN Y CAJAL, SANTIAGO (1852-1934)

Santiago Ramón y Cajal, born in the small Spanish town of Petilla de Aragón on May 1, 1852, was a major figure in the history of neuroanatomy. As related in his delightful autobiography, he was somewhat mischievous as a child and determined to become an artist, much to the consternation of his father, a respected local physician. Eventually, however, Ramón y Cajal entered the University of Zaragoza, and received a degree in medicine in 1873. As a professor of anatomy at Zaragoza, his interests were mostly in bacteriology until 1887, when he visited Madrid and first saw through the microscope histological sections of brain tissue treated with the Golgi method, which had been introduced in 1873.

Although few workers had employed this technique, Ramón y Cajal immediately saw that it offered great hope in solving one of the most vexing and fundamental problems in morphology: How do nerve cells interact with each other? This realization galvanized and directed the rest of his scientific life, which was extremely productive in originality, scope, and accuracy.

To place Ramón y Cajal's work in historical perspective, one must recall that, while studies of the gross anatomy of the brain can be traced back as far as Greek philosopher Aristotle, the first real insight into the disposition of its major fiber tracts was not gained until the middle of the nineteenth century, and even then the interpretation of this information was subject to great controversy. Shortly after the German botanist Jacob Schleiden, the German naturalist Theodor Schwann, and the German pathologist Rudolf Virchow proposed the cell theory in the 1830s, Joseph von Gerlach, Sr., and Otto Friedrich Karl Dieters suggested that nerve tissue was special in the sense that nerve cells are not independent units but instead form a continuous syncytium or reticular net. This concept was later refined by the Italian physician Camillo Golgi, who concluded that the axons of nerve cells form a continuous reticular net, whereas their dendrites serve a nutritive role, much like the roots of a tree.

Using Golgi's technique, Ramón y Cajal almost immediately arrived at the opposite conclusion, from his examination first of the cerebellum, and then of a wide variety of other sensory and motor systems. In short, he proposed that neurons interact by way of contact rather than continuity. His work on both the mature and the developing nervous system (he discovered the growth cone in 1890) provided the best evidence for the neuron doctrine (that neurons are independent units or cells, as in other tissues) until the introduction of the electron microscope in the 1950s.

Important as this evidence was, Ramón y Cajal's greatest conceptual achievement was the law of dynamic polarity. Based on his analysis of Golgiimpregnated neurons in the retina and other sensory systems, where the direction of information flow from the periphery to the central nervous system seems obvious, Ramón y Cajal concluded that, in general, the dendrites and perikaryon of a neuron receive information, whereas its axon transmits information. This brilliant generalization allowed him to lay out the basic organization of circuitry throughout the nervous system. This research was summarized in the monumental three-volume work Textura del sistema nervioso del hombre y de los vertebrados, published between 1899 and 1904, then expanded and translated into the definitive French edition, Histologie du système nerveux de l'homme et des vertébrés (1909-1911). This account deals systematically with all parts of the mammalian nervous system and many aspects of its development, and provides a great deal of information on the organization of the nervous system in fish, amphibians, reptiles, and birds.

Ramón y Cajal next examined in great detail the histological changes that can be observed during the degeneration and regeneration of neural tissue following damage. The results of this work were summarized in another monumental work that is still well worth reading, the two-volume Degeneration and Regeneration of the Nervous System, first published in Spanish in 1913-1914.

Ramón y Cajal received many honors, including the Nobel Prize, which he shared with a contentious Golgi in 1906. By the time Ramón y Cajal died, at the age of eighty-two in 1934, he had become one of the most famous and revered Spaniards of the twentieth century. In addition to the neurohistological work outlined herein, he wrote widely appreciated books on color photography, advice to young investigators, and well-known Spanish aphorisms.

Ramón y Cajal's description of the organization of cerebral cortical circuitry is unparalleled in depth and breadth. As early as 1894 he advanced the hypothesis that the remarkable intellectual growth seen in people who engage in continuous mental exercise is due to an enhanced elaboration of axon collaterals and dendritic processes within cortical circuitry.