A Brief History of the Neuron

Foreward

As I sit in this Kingston coffee shop, caffeine coursing through my system, a question Finlay asked resonates in my head: “What got you interested in neuroscience?” This is a hard question to answer; not because I can’t think of specific things that fascinate me about the field, but because it feels like the drive behind this passion is more profound than I had thought. After learning a bit about the pioneers of the field and performing some (quite daunting) acts of self-reflection, I’ve realized that my interest in neuroscience is a manifestation of a growing curiosity for how the world around me works. Since neuroscience is not just a single field but rather an intertwinement of both the arts and the sciences, I like to believe that it can help us to better understand not only ourselves, but the world around us.

The goal of this blog series will be to explore the enigma that is the human mind. I want it to be accessible and informative for people without a background in the sciences, while I also attempt to provide fresh perspectives and applications to other fields that everyone can find intriguing. As I’ve alluded to, neuroscience is an integration of a vast number of fields, and although physiology and psychology are usually the first to arise in conversation, other fields such as philosophy and computer science play significant roles, albeit in different ways. Throughout these blogs, I will attempt to explore the roles that these diverse fields play with regard to advancing neuroscience. Of specific interest to me are cognitive science, artificial intelligence, and deep brain stimulation (electrodes in the brain!), so if any of these topics sound interesting, or if you’d like to find out what they are, stay tuned for the next few blogs!

Disclaimer:

Please keep in mind that although I will try my best to provide reliable and up to date information, my content is not being peer-reviewed, unless you count my five undergraduate peers that will be proof-reading it! Consequently, feel free to refer to the sources I have cited and see what the experts have to say. Additionally, if you feel that anything I say needs to be corrected, please let me know and I will make the necessary changes.

The Neuron Doctrine

The study of the brain and its related systems predates even classical science; and as much as I’d like to delve into many of the very interesting discoveries that have contributed to the field, I am going to focus in on what was, in my opinion, the most revolutionary discovery in the field of neuroscience. I present to you the neuron doctrine. The neuron doctrine states that nerve cells (neurons) are the basic anatomic and functional units of the nervous system. In other words, the brain, spinal cord, and their associated extensions are made up of cells that, as we now know, are able to communicate via electrical impulses. Although this theory is now generally accepted, you may be surprised to learn that it was only in the early 1900s that the scientific community began to accept the notion that the brain was not, in fact, composed of a single, anatomically fused network of fibres, as was previously thought…

Some Background

In 1839, the ground-breaking “Cell Theory” was proposed. Theodor Schwann realized that every living thing is made of cells - and these cells, which come from pre-existing cells, constitute the basic unit of life. This helped scientists understand that organs, such as the heart, lungs, or eyes, are made up of specialized cells that serve specific functions. However, since scientists were not yet able to stain nerve tissue and view it under a microscope, there was still uncertainty as to what the brain was; was it a combination of specialized cells, just like in any other organ, or was it an organ in a class of its own?

Over time, it became evident that the nervous system was composed of a branching network of fibres. Joseph von Gerlach postulated that this network was made of a “reticulum of delicate fibres.” Essentially, this meant that cells in the brain are fused together, and sensory impulses flow directly through them. This theory, known as the reticular theory, became the generally accepted theory for years to come.

Enter Camillo Golgi: Clinical physician by day, ground-breaking biologist by night. After redesigning his hospital’s kitchen into a cell-research lab, he spent his free time feeding his curiosity for histology (as well his cell cultures). In 1873, with the objective of shedding light on the underlying components of nerve tissue, he was eventually able to develop a method that allowed him to visualize nerve cells under a microscope. The Golgi method, initially known as “La reazione nera” for its ability to stain a neuron black against a yellow background, revolutionized how the microscopic structure of the brain and spinal cord were observed for decades to come. Supported by his analyses, Golgi became a firm believer in the reticular theory, and argued that the structures he saw were simply parts of a larger network.

A few years later, we have the contributions of Santiago Ramón y Cajal. Although some aspects of his childhood may be considered to be slightly unorthodox, such as going grave-digging with his dad to practice sketching bones, the skills he learned helped him become one of the most important people in the history of science. By modifying Golgi’s staining method and applying it to developing embryonic tissue, he was able obtain clearer microscopic images of neurons, and thanks to his artistic abilities, he was able to produce excellent hand-drawn representations of his work.  Quickly, he began to notice that the cells making up nerve fibres are not only structurally independent, meaning they are separated by spaces which were later referred to as synapses, but they are also dynamic. If this is the case, then how can the reticular theory hold true? Based on his research, it couldn’t. As such, supported by a growing group of fellow scientists, he proposed the neuron theory, and prepared to face opposition for the indefinite future.

The Outcome

In 1906, both Golgi and Ramón y Cajal won the Nobel Prize in Physiology and Medicine for “revealing the inner beauty of the nervous system.” Cajal was accredited for developing the neuron doctrine which, without Golgi’s staining method, wouldn’t have been possible. Ironically, however, Golgi was opposed to the doctrine throughout his entire career. In fact, he dedicated his Nobel Lecture to the argument that the doctrine should be re-examined. He claimed that although most scientists supported the doctrine, and no clinician could ignore it without being considered out of date, he simply could not “abandon the idea of a unitary action of the nervous system.” Nevertheless, the neuron doctrine became, and continues to be, the accepted theory with which we interpret the nervous system today.

Perspective Is Everything

The neuron theory tells us that the nervous system is composed of individual, anatomically independent cells called neurons; but that is not the whole story. Since the development of the theory, our understanding of these cells has avalanched. We have been able to study the components of neurons and are now able to understand that they receive signals from cells and propagate them to other cells. However, neurons are not independent of the networks that they form. As it turns out, neurons are organized into extremely complex networks that are able to receive information, process it, and pass it along. If there are 86 billion neurons in the brain, and every neuron is able to communicate with 10,000 other neurons, how can we study the nervous system as a whole? This is where Golgi’s perspective makes a comeback. In order to study the nervous system, we can’t rely solely on a cellular approach; we must also take on a systems approach. This means looking at the brain not just as an organ composed of cells, but also as a series of circuits so complex that they put even the world’s best computers to shame. In broader terms, neuroscience requires looking at the brain through diverse perspectives, and it is only by the integration of these perspectives that we will ever come close to understanding not just the human brain, but the mind itself.

References

1. Fodstad, H., & Kondziolka, D. (2001). The neuron doctrine, the mind, and the Arctic. Neurosurgery, 47(6), 1381-1389. https://pubmed.ncbi.nlm.nih.gov/11126909/

2. Warmflash, D. (2017, February 12). Santiago Ramón y cajal and Camillo Golgi: Inside science. Visionlearning. Retrieved January 23, 2023, from https://www.visionlearning.com/en/library/Inside-Science/58/Santiago-Ramn-y-Cajal-and-Camillo-Golgi/233

3.     The nobel prize in physiology or medicine 1906. NobelPrize.org. (n.d.). Retrieved January 23, 2023, from https://www.nobelprize.org/prizes/medicine/1906/speedread/#:~:text=The%201906%20Nobel%20Prize%20in,beauty%20of%20the%20nervous%20system

4. Golgi, C. (1906). The neuron doctrine – theory and facts. Nobel Lecture December 11, 1906. https://www.nobelprize.org/uploads/2018/06/golgi-lecture.pdf