A Brief History of Neuroscience

Neurobiology profoundly influences our lives, impacting our health, thoughts, emotions, and behaviours (see How Our Neurobiology Shapes Our Daily Lives; Pang, 2023). Despite its importance, our scientific understanding of our nervous system only emerged recently, after many twists and turns, new inventions, and bitter rivalries. Here is a brief history of neuroscience.

Early concepts

Ancient Egyptians knew about neurology but did not see the brain as important and discarded it during mummification.

Source: Julia Kadel | Unsplash

Ancient Egyptian physicians already knew that injury to the spinal cord can result in paralysis and that brain lesions can impact speech functions (van Middendorp et al., 2010; Pang, 2023). Despite these insights, they valued the heart as the seat of the soul and did not see the brain as important, even discarding it during mummification (Guenot, 2022). Other ancient civilizations, like those in Mesopotamia and China, similarly did not place much emphasis on the brain or the nervous system (see Ancient Concepts of the Mind, Brain (and Soul); Pang, 2023).

Anatomical descriptions of the nervous system can be found in many texts from antiquity to early modern times. Bendetti likened it to “the roots and fibres of a tree” in 1497 and some early anatomists understood that this network could carry sensory information (Walsh, 2017). Some also noted that it can send signals outwards, with René Descartes imagining animal spirits—called pneuma—flowing through hollow nerves to inflate muscles like a hydraulic fluid (Ehrlich, 2022). Hydromechanics flourished during Descartes' lifetime—one of the many topics he studied (Gregory, 2017)—and was extensively used in the lavish fountains of the period and as a power source for early machines. This metaphorical comparison to the latest technological advancement continued for centuries: German anatomist Otto Deiters compared the nervous system to a railway network and Hermann von Helmholtz and Emil du Bois-Reymond likened it to a telegraph system (Ehrlich, 2022). This conceptual information exchange with engineering was not just one sided: The growing understanding of neurology inspired telegraph engineers like Samuel Morse—who invented the Morse code—and Werner von Siemens—who founded the German company named after him—to model telegraph networks after the nervous system, with great success (Ehrlich, 2022).

Microscopic revolution

Two key inventions revolutionised our understanding of the nervous system: The microscope and chemical staining.

Microscope designed and used by Robert Hooke in 1665.

Source: Public Domain (National Museum of Health and Medicine)

The term "microscope" was coined by the German doctor to the pope Johannes Faber—who was known in Italy as Giovanni Faber—in 1625 to describe an instrument Galileo invented in 1609 (Wollman et al., 2015). Although lenses existed for a long time, it was a family of Dutch spectacle makers who created the first microscope in around 1590 (Wollman et al., 2015). However, even with this new tool, the nervous system, with its densely packed neurons, looked just like a tangled mess when magnified (Ehrlich, 2022). A second invention was needed to birth modern neuroscience: Staining.

Towards the end of the 19^th century, the Italian biologist Camillo Golgi set up a rudimentary lab in the kitchen of his apartment near the University of Pavia where he taught histology. His goal was to try to decode the structure of the nervous system (Bentivoglio et al., 2019). While experimenting with different methods, he soaked nervous tissue in a potassium dichromate solution for several days. When he subsequently added silver nitrate, some—but crucially, not all—neurons turned black: For the first time, an entire neuron with all its structures could be seen under the microscope (Bentivoglio et al., 2019). Golgi called this the “black reaction” and this method is still used today, now known simply as the Golgi stain.

The reticular theory

Understanding of anatomy and histology flourished after the invention of the microscope. The English polymath Robert Hooke (a contemporary of Isaac Newton and his fiercest rival) noticed that cork consisted of hexagonally shaped cells (Crouvisier-Urion et al., 2019). This came as a complete shock at the time but gradually morphed into cell theory, the notion that all living organisms are made up of cells, which form the foundational building blocks and the basic structural and organisational units. However, prior to Golgi’s black reaction, individual neurons could not be observed, and many anatomists believed that the nervous system formed an exception to the general cell theory. The German anatomist Joseph von Gerlach suggested that the entire nervous system consisted of a single net through which protoplasm could freely flow (Bentivoglio et al., 2019). He referred to this network as the reticulum because of its fine netlike structure, and this idea became known as the reticular theory.

Perception can sometimes be shaped by beliefs. This was true for Camilo Golgi, who despite having been the first to see entire neurons held so strongly to the reticular theory (albeit a revised version) that he saw neural axons not as ending in a synapse but as being fused to other neurons, forming a reticulum (Guillery, 2005).

Drawing of neurons from a pigeon brain by Santiago Ramón y Cajal (1899).

Source: Public Domain (Wikimedia Commons)

The neuron doctrine

It took another leap to set neuroscience on a proper footing. The Spanish histologist Santiago Ramón y Cajal used Golgi’s staining method to extensively study the nervous system. His detailed drawings have not only led to countless discoveries but are still admired today for their scientific value (Cajal is often described as the father of modern neuroscience) and artistic beauty: His drawings have been shown at exhibitions and art galleries (Smith, 2018). In 1888 Cajal reported that neurons in the brains of birds were not continuous, suggesting that the nervous system is indeed made up of discrete cells, giving birth to a new theory, the neuron doctrine (López-Muñoz et al., 2006).

Golgi refused to accept this idea and the battle between the reticular theory and the neuron doctrine continued well after they both shared the Nobel Prize in physiology or medicine in 1906 (Grant, 2007). Although the neuron doctrine gained ground, it was not until the invention of the electron microscope that the issue was finally resolved for good in favour of the neuron doctrine (López-Muñoz et al., 2006).

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The fathers of modern neuroscience: Santiago Ramón y Cajal in his laboratory (left) and Camillo Golgi (right). They shared the 1906 Nobel Prize in physiology or medicine.

Source: Public Domain (Wikimedia Commons)