The intricate forest of the neuron

Silvia Maina
Torino, Italia

 

Drawing of a neuron by Santiago Ramón y Cajal
Santiago Ramón y Cajal. A Purkinje neuron from the human cerebellum. [Wikimedia, Public Domain]

Entering the room, I was welcomed by some small and attractive ink drawings. In the first, like a genealogical tree or a medieval miniature, thin branches stretched to fill the frame. In the second, waves of sea anemones wrapped into the algae that populates the sea floor.

The exposition, entitled Organisms and organized by The Gallery of Modern and Contemporary Art of Torino, displayed works about the connection between art and nature. And the fascinating drawings I was looking at are some of the most beautiful illustrations in the history of science.

What looked like a dense forest or a populated seabed designed in shifting combinations of ink and pencil are actually A Purkinje neuron from a human cerebellum (Figure 1) and Calyces of Held in the nucleus of the trapezoid body. The artist is the Nobel laureate and neuroanatomist Santiago Ramón y Cajal (1852–1934).

Born in Petilla de Aragón in 1852 in Spain, Ramón y Cajal was a pioneer of brain exploration and acknowledged as the founder of modern neuroscience. His studies answered fundamental questions, such as how nerve impulses travel between cells and the neurological basis of reflexes. His main theories, including the neuron doctrine and the law of functional polarization, still form the basis of our modern understanding of brain function.1

Cajal correctly intuited that neurons were separate from each other and somehow communicated, an idea that was even more amazing before the invention of the electron microscope.2 Cajal was able to apply his artistic eye to brain research. Where other contemporary neurologists, including Golgi himself with whom he shared the Nobel, only saw an impenetrable jungle of interlinked vines and branches, Cajal was able to untangle the apparent impenetrability of that woodland, distinguishing the individual neuronal strands. And, once identified, he began to draw them.

The eldest of four children, Santiago grew up in close contact with nature. From childhood, he showed a strong inclination towards the arts and the observation of nature. It was only to comply with his father’s wishes that Cajal turned his back on art to enroll in medical school in Zaragoza. After graduation, he became fascinated by histology—the study of tissues—and set up a microscope laboratory in his house (Figure 2).

It was in this small laboratory that his scientific career began. He routinely worked fifteen hours a day. “My work began at nine o’clock in the morning and usually lasted until around midnight,” he wrote in his Recuerdos de mi vida—Historia de mi labor cientıfica (Recollections of my life—The story of my scientific work). “Most curiously, my work caused me pleasure, a delightful intoxication, an irresistible enchantment.”3

In 1887 he became Professor of Histology and Pathological Anatomy at the University of Barcelona and in 1888 he founded his own journal: Revista trimestral de histología normal y patológica. The first volume (127 pages) included twelve original papers on the nervous system, which at the time was as unknown and enigmatic as outer space. Those papers were illustrated with twelve splendid engravings, carved in stone by Ramón y Cajal himself. This first volume included three papers on the cerebellum that are considered to be foundational. Moreover, his research of the cerebellum gave him the first evidence in favor of his neuron doctrine as opposed to the reticular theory. According to the neuron doctrine, nerve currents do not flow through a continuous network of neuronal processes, but are passed from one cell to the next by contact “in much the same way that electric current crosses a splice between two wires.”4

During the same period, he also discovered dendritic spines, axonal growth cones, and started his fundamental work in neuroembryology.5

Portrait of Ramón y Cajal
Ramón y Cajal (1884-1887), auto-portrait in Valencia. [Wikimedia,  Public Domain]

The interpretation of a brain section seen through a microscope is complex, and even more difficult to reproduce in a detailed drawing. But Cajal’s fascination and enthusiasm drove his research: “Like the entomologist in search of colorful butterflies,” he wrote, “my attention has chased in the gardens of the grey matter cells with delicate and elegant shapes, the mysterious butterflies of the soul, whose beating of wings may one day reveal to us the secrets of the mind.”

With use of a stain developed by Camillo Golgi in 1873 and modified by Cajal himself to better visualize cellular structures, he was able to visualize the whole neural cell and draw every detail of the cell and its processes. His intricate drawings were realized freehand, using ink on paper: the axon of Purkinje neurons in the cerebellum of a drowned man; the hippocampus of a man three hours after death; glial cells of the cerebral cortex of a child; the olfactory bulb of a dog; the retina of a lizard, are a few of his most famous works.

Cajal was a scientist who used other forms of creative expression as a clarifying force for scientific research. Although he was an experienced photographer (he also wrote a masterful book on this topic),6 drawings were necessary to illustrate his results because of the limitations of microphotography.3 He used his drawings to give form to his theories, as a way of thinking out loud. They were made with India ink and touched-up with white gouache. Even his corrections are impressive, because they testify to the deep analysis needed to reach the final result, which Cajal obtained with precise study of many preparations. From each preparation, he could extract a partial view of a general pattern of organization.

Not all visitors to the Organisms exhibition were scientists, but everyone was fascinated by these drawings as pure art. The neuron, which Cajal called “the noble and enigmatic cell of thought,” reminds us of lost landscapes, marine life, and breathing forests.

As he himself wrote in the epilogue of Recollections: “The forest of dormant brain neurons must be shaken vigorously; it is necessary to make them vibrate with the emotion of the new and infuse them with noble and high concerns.”3 This is what his drawings still do: shake the forest of our dormant neurons.

 

References

  1. Andres-Barquin PJ. Ramón y Cajal: a century after the publication of his masterpiece. Endeavour. 2001 Mar;25(1):13-7. doi: 10.1016/s0160-9327(00)01334-x. PMID: 11314455.
  2. Georgopoulos AP, Georgopoulos A. The Beautiful Brain and the Influence of Santiago Ramón y Cajal on Medicine. JAMA. 2017 Aug 8;318(6):502-504. doi: 10.1001/jama.2017.9858. PMID: 28787487.
  3. Recuerdos de mi vida-Historia de mi labor cientıfica (“Recollections of my life—The story of my scientific work”), 1917, https://cvc.cervantes.es/ciencia/cajal/cajal_recuerdos/recuerdos/labor_27.htm
  4. DeFelipe J. Cajal and the discovery of a new artistic world: the neuronal forest. Prog Brain Res. 2013;203:201-20. doi: 10.1016/B978-0-444-62730-8.00008-6. PMID: 24041282.
  5. Sotelo C. Viewing the brain through the master hand of Ramón y Cajal. Nat Rev Neurosci. 2003 Jan;4(1):71-7. doi: 10.1038/nrn1010. PMID: 12511863.
  6. Ramón y Cajal, S. La Fotografía de los Colores: Fundamentos Científicos y Reglas Prácticas (Moya, Madrid, 1912).

 


 

SILVIA MAINA has a degree in pharmaceutical chemistry and works in the medical publishing field, assisting clinicians in the creation of editorial projects. She is a member of the Editorial Board of European Science Editing (ESE), the journal of the European Association of Science Editors.

 

Summer 2021  |  Sections  |  Neurology