Most Mysterious Human Organ

Hieroglyphic for the word “brain” (c.1700 BCE)

Source: The Edwin Smith Surgical Papyrus (17th century BCE), Public Domain, Wikipedia Commons

 

From the ancient Egyptian mummifications to 18th century scientific research on “globules“ and neurons, there is evidence of neuroscience practice throughout the early periods of history. The early civilizations lacked adequate means to obtain knowledge about the human brain. Their assumptions about the inner workings of the mind, therefore, were not accurate. Early views on the function of the brain regarded it to be a form of “cranial stuffing“ of sorts. In ancient Egypt, from the late Middle Kingdom onwards, in preparation for mummification, the brain was regularly removed, for it was the heart that was assumed to be the seat of intelligence.

 

According to Herodotus, during the first step of mummification: “The most perfect practice is to extract as much of the brain as possible with an iron hook, and what the hook cannot reach is mixed with drugs.“ Over the next five thousand years, this view came to be reversed; the brain is now known to be the seat of intelligence, although colloquial variations of the former remain as in “memorizing something by heart“.

 

The Edwin Smith Surgical Papyrus, written in the 17th century BCE, contains the earliest recorded reference to the brain. The hieroglyph for brain, occurring eight times in this papyrus, describes the symptoms, diagnosis, and prognosis of two patients, wounded in the head, who had compound fractures of the skull. The assessments of the author (a battlefield surgeon) of the papyrus allude to ancient Egyptians having a vague recognition of the effects of head trauma. While the symptoms are well written and detailed, the absence of a medical precedent is apparent. The author of the passage notes “the pulsations of the exposed brain“ and compared the surface of the brain to the rippling surface of copper slag (which indeed has a gyral-sulcal pattern). The laterality of injury was related to the laterality of symptom, and both aphasia (“he speaks not to thee“) and seizures (“he shutters exceedingly“) after head injury were described. Observations by ancient civilizations of the human brain suggest only a relative understanding of the basic mechanics and the importance of cranial security. Furthermore, considering the general consensus of medical practice pertaining to human anatomy was based on myths and superstition, the thoughts of the battlefield surgeon appear to be empirical and based on logical deduction and simple observation.

 

During the second half of the first millennium BCE, the Ancient Greeks developed differing views on the function of the brain. However, due to the fact that Hippocratic doctors did not practice dissection, because the human body was considered sacred, Greek views of brain function were generally uninformed by anatomical study. It is said that it was the Pythagorean Alcmaeon of Croton (6th and 5th centuries BCE) who first considered the brain to be the place where the mind was located. According to ancient authorities, “he believed the seat of sensations is in the brain. This contains the governing faculty. All the senses are connected in some way with the brain; consequently they are incapable of action if the brain is disturbed, the power of the brain to synthesize sensations makes it also the seat of thought: The storing up of perceptions gives memory and belief and when these are stabilized you get knowledge.“ In the 4th century BCE Hippocrates, believed the brain to be the seat of intelligence (based, among others before him, on Alcmaeon’s work). During the 4th century BCE Aristotle thought that, while the heart was the seat of intelligence, the brain was a cooling mechanism for the blood. He reasoned that humans are more rational than the beasts because, among other reasons, they have a larger brain to cool their hot-bloodedness.

 

In contrast to Greek thought regarding the sanctity of the human body, the Egyptians had been embalming their dead for centuries, and went about the systematic study of the human body. During the Hellenistic period, Herophilus of Chalcedon (c.335/330 – 280/250 BCE) and Erasistratus of Ceos (c. 300 – 240 BCE) made fundamental contributions not only to brain and nervous systems’ anatomy and physiology, but to many other fields of the bio-sciences. Herophilus not only distinguished the cerebrum and the cerebellum, but provided the first clear description of the ventricles. Erasistratus used practical application by experimenting on the living brain. Their works are now mostly lost, and we know about their achievements due mostly to secondary sources. Some of their discoveries had to be re-discovered a millennium after their death.

 

During the Roman Empire, the Greek anatomist Galen dissected the brains of sheep, monkeys, dogs, swine, among other non-human mammals. He concluded that, as the cerebellum was denser than the brain, it must control the muscles, while as the cerebrum was soft, it must be where the senses were processed. Galen further theorized that the brain functioned by movement of animal spirits through the ventricles. “Further, his studies of the cranial nerves and spinal cord were outstanding. He noted that specific spinal nerves controlled specific muscles, and had the idea of the reciprocal action of muscles. For the next advance in understanding spinal function we must await Bell and Magendie in the 19th Century.“ Circa 1000, Al-Zahrawi, living in Islamic Iberia, evaluated neurological patients and performed surgical treatments of head injuries, skull fractures, spinal injuries, hydrocephalus, subdural effusions and headache. Concurrently in Persia, Avicenna also presented detailed knowledge about skull fractures and their surgical treatments. Between the 13th and 14th centuries, the first anatomy textbooks in Europe, which included a description of the brain, were written by Mondino de Luzzi and Guido da Vigevano.

 

Andreas Vesalius noted many structural characteristics of both the brain and general nervous system during his dissections of human cadavers. In addition to recording many anatomical features such as the putamen and corpus collusum, Vesalius proposed that the brain was made up of seven pairs of ‘brain nerves’, each with a specialized function. Other scholars furthered Vesalius’ work by adding their own detailed sketches of the human brain. Ren? Descartes also studied the physiology of the brain, proposing the theory of dualism to tackle the issue of the brain’s relation to the mind. He suggested that the pineal gland was where the mind interacted with the body after recording the brain mechanisms responsible for circulating cerebrospinal fluid. Thomas Willis studied the brain, nerves, and behavior to develop neurologic treatments. He described in great detail the structure of the brainstem, the cerebellum, the ventricles, and the cerebral hemispheres.

 

The role of electricity in nerves was first observed in dissected frogs by Luigi Galvani in the second half of the 18th century. In the 1820s, Jean Pierre Flourens pioneered the experimental method of carrying out localized lesions of the brain in animals describing their effects on motricity, sensibility and behavior. Richard Caton presented his findings in 1875 about electrical phenomena of the cerebral hemispheres of rabbits and monkeys. Studies of the brain became more sophisticated after the invention of the microscope and the development of a staining procedure by Camillo Golgi during the late 1890s that used a silver chromate salt to reveal the intricate structures of single neurons. His technique was used by Santiago Ramon y Cajal and led to the formation of the neuron doctrine, the hypothesis that the functional unit of the brain is the neuron. Golgi and Cajal shared the Nobel Prize in Physiology or Medicine in 1906 for their extensive observations, descriptions and categorizations of neurons throughout the brain. The hypotheses of the neuron doctrine were supported by experiments following Galvani’s pioneering work in the electrical excitability of muscles and neurons. In the late 19th century, Emil du Bois-Reymond, Johannes Peter Muller, and Hermann von Helmholtz showed neurons were electrically excitable and that their activity predictably affected the electrical state of adjacent neurons. In parallel with this research, work with brain-damaged patients by Paul Broca suggested that certain regions of the brain were responsible for certain functions.

 

Tell me where is fancie bred,

In the heart or in the head?

 

William Shakespeare (Merchant of Venice)

 

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