Santiago Ramón y Cajal (1852-1934)
The Godfather of Modern Neuroscience

(New June 2007)
A page from: Eric Hargreaves'Page O'Neuroplasticity

Portrait of young Ramon Y Cajal at work in his lab Ramon Y Cajal is oft referred to as the father of modern neuroscience, but after having read a number of translated works, especially on the scientific process "Reglas y Consejos sobre Investigación Scientifica (very loosely translated as: Advice to a young investigator 1916 Trans 1989)" his autobiography "Recuerdos de mi vida (Recollections of my life; 1917 Trans 1989)" and "Neuronismo o Reticularismo? (Neuron Theory or Retular Theory; 1933 Trans 1954)", I prefer to refer to him as the "Godfather" of modern neuroscience: Elegantly heavy handed, persuasive, making an argument you can't refuse.

Self-portrayed at right, when he was a young professor at Valencia in the makeshift laboratory set up in his kitchen. It was here that Cajal started studying the nervous system in 1885, at age 35, using a newly awarded modern Zeiss microscope. Originally the work was intended to generate illustrations for a book on histological techniques Manual de Histología normal y Técnica micrográfica (Manual of normal histology and micrographic technique, published eventually in 1889), but within a couple of years, frustrated by the staining techniques of the times, he travelled from Valencia to Madrid in 1887 to get updates on any new advances.

Golgi's "la reazione nera"

During his trip to Madrid, Cajal saw his first slides impregnated with Camillo Golgi's 1873 "la reazione nera" or "black reaction" at the home laboratory of Luis Simarro Lacabra. Recently back from a number of years in Paris, Lacabra had learned of the technique from the famour histologist Louis Antoine Ranvier. In an historical irony, the French histologist Ranvier was disdainful of Camillo Golgi's published technique, believing it to be far too capricious to be useful. Ranvier's opinion is not that far off the mark, since even today it is largely unknown as to why so few, and which neurons become impregnated with the Golgi technique.

Armed with the new technique Cajal was enthused and enthralled, writing much later in his autobiography of this moment "...coloured brownish black even to their finest branchlets, standing out with unsurpassable clarity upon a transparent yellow background. All was sharp as a sketch with Chinese ink," (Cajal, 1917).

One of Cajal's slides labelled bbb for bueno, indicating quality The next two figs on the left, are why I remain amazed at what can be found on the web. First up is an actual slide of Cajal's (not necessarily of a Golgi impregnation), but complete with his handwritten labels, identifying the slide as "bueno, bueno, bueno", for its good quality.

Photomicrograph from one of Cajal's Golgi preparations, a Pryamidal cell in the cerebral cortex This is followed by an even more amazing pic, a modern photomicrograph taken of a small segment of one of Cajal's original Golgi slides. How cool is that? Here, one is literally peering in at a small segment of history that has had major implications for where Neuroscience is today. Even though the slide is over a century old, for its clarity, the photomicrograph may have been taken of a specimen stained and coverslipped within less than a week. The segment itself depicts a single, but well outlined (as though in Chinese ink), pyramidal cell from the cerebral cortex. Regardless, independent of each other Lacabra, Kolliker and Cajal, produced more stable and reliable variants of the Golgi process. Cajal's modification of the Golgi technique was to re-impregnate the slide with silver nitrate a second time, thus producing a further and more complete penetration. So although developed by Camillo Golgi, it was in the hands of Santiago Ramon Y Cajal that the technique flourished.

The Neuron Doctrine

Moving to Barcelona to accept the chair of Normal and Pathological Histology at the end of 1887, the flury of work that ensued over the next few years were to bring about the "Neuron Doctrine" and to establish the law of "Dynamic Polarization", embedded within the Doctrine.

Reticular Theory

At the time, although cells were accepted as the basic unit for the rest of the body (Virchow, 1855), the nervous system was considered by many to be a finely wrought mesh of continuously connected fibres or "reticulum", the proponents of which included Camillo Golgi. The development of the Reticular Theory of the nervous system, not unlike the Neuron Doctrine, also had a lot to do with the histological techniques that were current in the mid nineteenth century. So although cell bodies of neurons could be identified with some stains, the supposed continuous nerve fibres or filaments of such long tracts, as those found in the spinal cord, were frequently idenfied separately with myelin stains. Based on such gold chloride stains of the spinal cord that he had developed himself, Josef von Gerlach formulated the first postulation of what became the widely accepted Reticular Theory (Gerlach, 1871).

Meanwhile back in Barcelona, and employing his own "double-dipping" refinement to the new silver technique Cajal began to rapidly publish results in a journal of his own making. The journal lasted 5 years as Cajal's initial conception "Revista Trimestral de Histologia Normol y Patologica" (Quarterly review of normal and pathological histology), before being taken up by the University of Madrid as "Trabajos del Laboratorio de Investigaciones Biologicas de la Universidad de Madrid" (Communications of the Laboratory for Biological Research, Madrid University), subsequently, alternative issues were published in french, and following the Spanish Civil War another name was invoked, followed by a final naming by the Cajal Institute (DeFelipe and Jones, 1992). During the initial run of the Journal Cajal published 11 articles (Lopez-Munoz, Boya and Alamo, 2006).

Critical Evidence

Two critical papers of Cajal's were published during this time. The first paper showed that basket cell axons from the molecular layer of the embryonic chick cerebellum terminated with ramifications that engulfed the purkinje cell bodies (Cajal,1888a). The second paper showed that the parallel fibres of the cerebellar molecular layer were bifurcations of axons originating from granule cells that terminated "en passant" across many purkinje cell dendritic trees. In contrast, the axons of the climbing fibres originating from the deep nuclei terminated on a single purkinje cell at a dendritic level more proximal to the cell body than that of the parallel fibres (Cajal,1888b). Together, Cajal interpretated these findings to assert the independence of neurons from each other, indicate a uni-directional pattern of cellular contiguity, and identify more than a single type of parallel termination. These findings when summarized together together with others (Cajal, 1889a), formed the critical mass necessary for Cajal to become a vocal proponent in favour of the independence of neural units, along with the principle of dynamic polarization in what would eventually become the Neuron Doctrine (Lopez-Munoz, Boya and Alamo, 2006).

Publishing Politics

However, since Spanish science, and therefore Spanish science publications, were not at the forefront of the scientific community, Cajal in late 1889 travelled to the Congress of the German Anatomical Society held in Berlin. There, armed with his slides and drawings Cajal was able to persuade a number of prominent histologists, including Rudolf von Kolliker, and Heinrich Wilhelm von Waldeyer of the importance of his findings, and the correctness of his interpretation. Of these two histologists, Kolliker's support allowed Cajal to recapitualte his findings in two subsequent articles written in french, and published in two of the more prestigious German journals (Cajal, 1889b,1889c). The first article summarized Cajal's work on the bird retina, and the second covered his work in the cerebellum (Lopez-Munoz, Boya and Alamo, 2006). Waldeyer, the latter of the two prominent German histologists combining Cajal's evidence, along with that of others, was the first to formally state the Neuron Doctrine in a series of short interspersed articles of a single issue of the prominent Deutsch Medizinische Wochenschrift (German Medical Weekly,1891).

Cajal's Neuron Doctrine

In his own words (albeit tanslated) Cajal later set forth his own not too different version of the Neuron Doctrine, outlining its four basic tenets as:
"1.) The collateral and terminal ramifications of all axis-cylinders [axons] end in the grey matter, not by means of a diffuse network, as argued by Gerlach, Golgi and the majority of neurologists, but by means of free arborizations, disposed in a variety of forms (pericellular baskets or nests, climbing branches, etc.).

2.) These [axonal] ramifications apply themselves intimately to the body and dendrites of the nerve cells, establishing a contact or articulation [synapses] between the receptor protoplasm [dendrites] and the final, tiny axonic branches.

3.) Given that the body and dendrites of neurons are applied narrowly to the final tiny roots of the axis-cylinders, it is necessary to accept that the body and the protoplasmic processes participate in the chain of conduction, that is, that they receive and propagate the nervous impulse, in contrast to the opinion of Golgi, for whom these cell segments would play a merely nutritive role.

4.) The exclusion of substantial continuity between cell and cell leaves the way open for the opinion that the nervous impulse is transmitted by contact, as in the articulations of electrical conductors, or by a kind of induction, as with induction coils. (Cajal, 1917; Trans: 1989).

Although grateful for Waldeyer's early support of his work and ideas, Cajal was later to set down the final and lasting record of events in 1933, a decade after Waldeyer's death, and a mere year before Cajal's own.

"Professor Waldeyer, to whom poorly informed persons attribute the neuron theory, supported it with the prestige of his authority but did not contribute a single personal observation. He limited himself to a short, brilliant exposition (1891) of the objective proofs adduced by His, Kollicker, Retzius, Van Gehuchten and myself, and he invented the fortunate term of neuron" (Cajal, 1933; Trans: 1954 p3).

Reasons for Cajal's Success

Today, it is acknowledged that the impetus behind the "Neuron Doctrine" was largely derived from Cajal, and that the work of Cajal based on the Golgi techique ushered in the "golden age" of neuroanatomy.


However, it was not just the refinement of Golgi's technique that permitted Cajal to make the great strides that he did. One discovers quickly upon reading his autobiographical, and more semi-philosophical works that Santiago Ramón y Cajal possessed an indominatable personality. As is often the case in research, personality is more of a factor than sheer brilliance, and although it is evident that Cajal had both, his doggedness of pursuit, and tenacity of will are likely to have sustained his research program more than his brilliance. In the end his results are based on countless slides and on a self procclaimed "millions of neurons strongly stained by different methods of impregnation" (Cajal, 1933; Trans: 1954).


Of course there was brilliance, or at least a certain degree of cleverness. First, as expected, Cajal did study human material as did most histologists of his day, however, he more frequently examined simpler species with smooth cortices, and less mylenation, such as birds and small mammals. Second, he studied many ontologically earlier or immature specimens not fully developed, where the neurons had yet to reach their full level of complexity or density. Third and final, he preferred highly laminated structures, such as the cerebellum, retina, and hippocampus, since these structures provided clear stratification of axonal plexuses and cell types (Jones, 1999).

A Little Luck

Finally, as is often the case in research Cajal had a little luck. By being isolated as he was from the rest of the mainstream european academic community and as a result less literature resources, Cajal may not have been as easily influenced by the thinking of the times, as he was influenced by his own observations. Further, luck may have played a role in being awarded the modern "state of the art" Zeiss microscope by the Provincial Government of Zaragoza, since the award was recieved in recognition for his tireless labour during a cholera epidemic. Then again it may have been Cajal himself who requested the Zeiss in lieu of some other reward, again suggesting the single mindedness with which he viewed his research.

The Nobel Prize

Regardless, for contributions that led to the Neuron theory and his meticuluous work that followed in describing the human neuroanatomy Santiago Ramon Y Cajal was awarded the 1906 Nobel prize for Medicine along with Camillo Golgi for the development of the silver nitrate impregnation. Of course, Golgi in 1906, still a staunch Reticularist delivered his acceptance speech as an all out, but scathingly polite, attack on the Neuron Doctrine. However, having moved on to other things during his career, Golgi's knowledge of the current literature had ceased some 15 years prior to the award and most of the corroborating data supplied to support his own evidence reflected the lack of modern evidence. The next evening, Cajal delivered his acceptance speech, given in the form of a simple assertion of the Neuron Doctrine, backed up by an avalanche of his own data, corroborated by a host of modern researchers and contemporaries. It is the only time in the history of Sweden's Nobel Prize (for any area awarded) that two individuals on opposing sides of such a fundamental issue were both awarded the gift simultaneously. Although by those in the "know", the weight of evidence was swiftly falling in favour of Cajal, at the time it was yet to be widely accepted by the scientific and medical community. Ultimately, the Neuron vs. Reticular theory of the Nervous System organization was resolved in the 1930s with the development off the electron microscope. Regardless, both essays are worth reading for being fundamentally opposed to each other and both are available from the Nobel Prize website itself.
Download Golgi's acceptance speech (PDF 462kb)
Download Cajal's acceptance speech (PDF 705kb)

Magnum Opus and its many Translations

Of course all of this has little to do with the hippocampus itself, except that the dentate gyrus and Ammon's horn being one of the highly laminated structures that both Golgi and Cajal favoured. However, once Cajal had accumulated enough experience in viewing ontologically earlier samples from lower vertebrates, he did turn to the intricate and delicate, if not somewhat tedious task, of cataloging and describing human neuroanatomy. In doing so Cajal produced his magnum opus and possibly his most lasting work, "Textura del Sistema Nervioso del Hombre y los Vertebrados" (VolI: 1899 + VolII: 1904), especially after being translated from the original Spanish into the more popular French as "Histologie du Système Nerveux de l'Homme et des Vertébrés", translated by L. Azoulay with some additional editing and figures by Cajal, published in 1909 and again 1911 by Maloine, Paris. Of course apart from enviously viewing many of the figures, I had to wait until 1995 for an English translation (Neely and Larry W. Swanson, published in 1995 by Oxford University Press). Not surprising, Larry W. Swanson has translated a number of Cajal's other works directly from the original Spanish. Yet, for this work the Swansons chose the 1911 French edition. It is only odd in that Larry W. Swanson is not simply a translator with a propensity towards Cajal, but another neuroantomist with hippocampal interests. It has been suggested that Cajal was not always well served by his translators, especially works translated to French and/or German, by non-native spanish speakers, many of whom were translating based on their knowledge of latin (Jones, 2001). However, starting in 1999 for Volumes I and II, and continuing in 2001 for Volume III, Pedro and Tauba Pasik through Springer-Verlag/Wein Press, released a second English translation based on the original Spanish trying to keep Cajal's original emphasis, as well as supplementing many of Cajal's original (and sometimes arcane) terms with present day and common terms. Embedded within this great tome are a continuance and repitition of Cajal's ideas again and again. Simply not content to describe and define, Cajal continually pushes the envelope with his agenda of ideas about the Nervous System.

Cajal's Hippocampus

Cajal's hippocampus Regardless, at right is one of the more famous of Cajal's hippocampal drawings from Histology of the Nervous System of Man and Vertebrates. The picture of the hippocampus was used to adorn the cover of the journal by the same name for a number of years in the early 1990s, when the journal was first getting started. From the sparsely drawn transverse section, one can see all the pathways of the tri-synaptic circuit. The perforant-path arising from the entorhinal cortices and doing exactly that crossing into the dentate gyrus to synapse onto the principal layer of granule cells. The Granule cells' mossy fibre system in turn, synapsing en passant with the pyranidal cells of CA3. The Schaffer collaterals of CA3 re-entering the stratum radiatum and synapsing onto the CA1 pyramidals to complete the ciruit. By only outlining a few of the connections in the circuit Cajal, permits one to appreciate the orderilness of the laminar structure and the law of dynamic polarization, as cells synapse with each other end to end to end. Finally, he has also indicated the flow of information according to the contiguity of the cells, aiding us with his playful little arrows.

Elderly Cajal

Cajal References...

Cajal, SRY (1888a). Estructura de los centros nerviosos de las aves. Revista Trimestral de Histologia Normol y Patologica, 1, 1-10.

Cajal, SRY (1888b). Sobre las fibras nerviosas de la capa molecular del cerebelo. Revista Trimestral de Histologia Normol y Patologica, 1, 33-49.

Cajal, SRY (1889a). Conexion general de los elementos nerviosos. Medical Practica, 2, 341-346.

Cajal, SRY (1889b). Sur le morphologie et lesconexions des elements de la retine des oiseaux. Anatomischer Anzeiger, 4, 111-121.

Cajal, SRY (1889c). Sur l'origene et la direction des prolongations nerveuses de la couche moleculare du cervelet. Internationalen Monatsschrift fur Anatomie und Physiologie, 6.

Cajal, SRY (TomoI:1899 + TomoII:1904) Textura del Sistema Nervioso del Hombre y los Vertebrados, Imprenta y Liberia de Nicolas Moya, Madrid.

Cajal, SRY (1909 1st Ed. + 1911 2nd Ed.) Histologie du Système Nerveux de l'Homme et des Vertébrés, Translated by L. Azoulay, Maloine, Paris.

Cajal, SRY (1995 Vols I & II) Histology of the Nervous System of Man and Vertebrates. Translated (from the French) by Neely and Larry Swanson. New York, NY: Oxford University Press, Oxford.

Cajal, SRY (VolI & VolII: 1999 + VolIII: 2001) Texture of the Nervous System of Man and the Vertebrates. Translated by Pedro and Tauba Pasik. Spring-Verlag/Wein SpringerBarcelona, printed in Slovenia.

Cajal SRY (1916). Advice for a Young Investigator. Translators: Neely Swanson and Larry Swanson 1999, MIT PRess. Cambridge Massachussettes.

Cajal SRY (1917). Recollections of my Life. E.H. Craigie & J. Cano Trans, MIT Press 1989.

Cajal SRY (1954). Neuron Theory or Reticular Theory? Objective Evidence of the Anatomical Unity of Nerve Cells. Translators: U.M. Purkiss and Fox C.A. Consejo Superior de investigaciones cientificas instituto Ramon Y Cajal, Madrid.

DeFelipe,J. and Jones, E.G. (1992) Santiago Ramon Y Cajal and methods in neurohistology. Trends in the Neurosciences, 15, 237-246.

Gerlach, J., Von dem Rückenmark. In: Handbuch der Lehre der Gewebe des Menschen und der Thiere. Ed: Stricker S., W. Engelmann; Leipzig: 1871. pp. 665–693.

Jones, EG (1999). Gogi Cajal and the Neuron Doctrine. Journal of the History of the Neurosciences, 8, 170-178.

Jones, EG (2001). Cajal made clear in translation. Nature, 412, 19-20.

Lopez-Munoz, F., Boya, J., and Alamo, C. (2006) Neuron theory, the cornerstone of neuroscience, on the centenary, of the Nobel Prize award to Snatiago Ramon Y Cajal. Brain Research Bulletin, 70, 391-405.

Lorente de No, R. (1934). Studies on the structure of the cerebral cortex II, continuation of the study of the ammonic system. Journal fur Psychologie und Neurologiey, 46, 113-177.

Titford, M. (2005). The long history of hematoxylin. Biotechnic & Histochemistry, 80, 73-78.

Virchow, R. (1855). Cellular-pathologie, Virchows Archiv, 8, 3-39.

Waldeyer, HWG (1891). Ueber einige neuere Forschungen im Gebiete der Anatomie des Centralnervensystems (About some new researche in the field of anatomy of the central nervous system). Deutsch Medizinische Wochenschrift, 17, 1213-1218, 1244-1246, 1287-1289, 1331-1332, 1352-1356.