Now for a concise history of the study of the nervous system, starting back in the days of the Greek and Roman Empires.
Hippocrates (c. 460–377 BC), widely regarded as the ‘Father of Western Medicine’, was a Greek physician who instituted a shift in the thinking and practice in medicine. Before Hippocrates, religion was the accepted paradigm to describe, explain and predict events – and doctors were in fact priests, whom patients would seek in temples for religious healing through prayer and purification. Under the influence of Hippocrates, medicine moved away from religion and towards the use of nature to diagnose, explain and treat illness. Doctors were trained as physicians – students of nature – and they practised a craft instead of religious rituals. In contrast to his predecessors, who believed that the heart was the centre for the soul and control of the body, Hippocrates believed that the mind was in the brain and controlled the body, but that it was something intangible. Hippocrates was uniquely different from his contemporaries in that he believed that disease and head injuries, not demons and evil spirits, caused madness and affected coordination. Hippocrates was prolific and wrote an impressive body of work, known together as the Corpus Hippocraticum, comprising treatment manuals, speeches, notes and books. One important point to make here is that there is no evidence that Hippocrates and his physicians ever dissected a human – or in fact any organism. At the time of Hippocrates, the Greeks believed that interfering with the human body after death was tantamount to sacrilege, while many Greeks were also believers in reincarnation. So it is not entirely clear on what evidence the Hippocratic Corpus was based.
Plato (428–348 BC), a Greek philosopher, agreed with Hippocrates in believing that the mind was in the head. However, he also believed that the mind and the body were separate, and that we reach the truth not via our senses but through our thoughts, i.e. by logic and reasoning. In other words, the senses cannot be trusted.
Aristotle (384–322 BC) was both Plato’s student and rival – anyone know that feeling! Aristotle was a keen dissector, who studied the anatomy of almost 50 species. In contrast to Plato, Aristotle felt that he could trust his senses. From his observations that the heart moved and was filled with blood, and that it felt warm, he deduced that this organ was vital to life – the heart was ‘the acropolis of the body’ (Finger 2000). In contrast, the brain looked still and bloodless, and he deduced from this that the brain must act as a cooling system for the heart! So Aristotle’s model was that the heart was the seat of our emotions. He also argued that the mind and the brain were one, and that the mind was entirely physical – in other words, we can only understand the mind by studying the body.
Remember that, so far, human autopsy was not allowed in the Golden Age of Greece, due to religious beliefs. However, after Hippocrates’ death, much changed in Greek society, and Alexandria in Egypt had developed itself into one of the great places for academic study, of which medicine was one.
Human dissection was led by Herophilus of Chalcedon and Erasistratus, around 300 BC. Erasistratus was also the first to notice and comment on the fact that the human brain had many more wrinkles in comparison to the animal, which he equated to a greater ‘brain power’. However, this was an opinion, which was later questioned by Galen.
Galen (AD 129–199) was a Graeco-Roman physician to the gladiators and is widely regarded as the founder of experimental physiology. Like Aristotle, Galen felt that the truth is only conveyed through the senses, but unlike any of his predecessors, he took systematic observation and dissection to a new height. Thereby, he introduced a paradigm shift in medicine and transformed it into an applied science. Galen’s interest in understanding how the body works may have been inspired by his father, who was an architect, and Galen diligently dissected animals in an attempt to reveal their internal structure. However, he did not perform human autopsies, as the Roman religious and legal systems did not permit this. His knowledge and understanding of human anatomy and physiology were most likely based on his observations of wounded gladiators – of which there appeared to be plenty. In contrast to Aristotle, however, Galen noted that the brain did not feel cool, and that nerves went to the brain – not the heart. He could, therefore, not accept Aristotle’s model of the brain as a ‘radiator’. By additionally noting that the cerebrum felt softer compared to the cerebellum, Galen postulated that the former was the seat of sensation, while the latter was the commander of muscles. Although this model would inevitably be considered rather crude and simplistic today, an element of truth remains, albeit based on a different rationale. So far, so good. However, Galen also postulated a physiological model of the brain, which was based on hydraulics. He thought that nerves were hollow, and that body fluids (the cerebrospinal fluid or CSF) moved between nerves and ventricles (the cavities within the brain). Moreover, Galen believed that the CSF was the psychic fluid (the fluid of the mind) and when he discovered the ventricles, where the CSF collects, he believed that he had found the seat of the mind. Clearly, although Galen was a brilliant anatomist, his model of the physiology of the nervous system was deeply flawed. However, his theories would not be challenged for centuries.
It is then safe to say that we had a bit of a gap, of about 1300 years, which takes us through the Middle Ages – a time of intellectual darkness and untested beliefs in the absence of any experimentation – a time when Galen’s ideas became dogma. Interest in research began to gather some pace again with the Renaissance in the 14th century.
Andreas Vesalius (1514–1564), was a rather adventurous Flemish anatomist, who took considerable risk by illegally removing cadavers from cemeteries and collecting recently deceased bodies from the gallows, in order to study their anatomy. He carefully noted his observations and compiled the beautifully crafted De humanis corporis fabrica (on the workings of the human body), a groundbreaking publication of 663 pages long, produced at the tender age of 28 years (Vesalius, 1543). Vesalius worked as a member of the academic faculty in Padua, where people from all over the world came to observe his anatomical lessons. Gradually, Vesalius realised that many of the statements made by Galen could not be supported by his own observations. It took him a while to realise the reasons for these discrepancies; Galen had only ever performed dissections on animals! Vesalius’ contribution to medical science was, therefore, the introduction of a human anatomy. Finally, Vesalius also discredited Aristotle’s idea that the mind, and the seat of our feelings, was in the heart – he insisted that it was in the brain. He must have been quite insistent as no one has since doubted his assertion!
As we saw above, human autopsies were generally not accepted in Vesalius’ time and the University of Padua was an exception. It required another paradigm shift for society to accept the practice of opening the human body after death – which eventually came from an unexpected source.
The French philosopher, René Descartes
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