Spirits, Brains And Minds
The Historical Evolution of Concepts on the Mind
Ramon M. Cosenza, MD, PhD
Nowadays, even lay people know that the brain is the organ that controls behavior and mental skills. Educated people also know that chemical and electric phenomena lay behind the functioning of the nervous system. However, all this knowledge is quite recent and during many centuries what people considered to be true about the functioning of the brain was completely different from what we know today.
Mankind has been linking mind to the brain the for a long time. Human skulls with holes deliberately made in them were found in sites more than 10.000 years old. Probably, those holes were made in order to grant a way out for the bad spirits that should be tormenting those brains [4].
The link between brain and mental functions was a natural one to achieve, because primitive people in all ages could easily observe that strong blows to the skull resulted in loss of consciousness and of memory, and even convulsions, which often led to significant alterations of perception and behavior.
The best and most important documental proof about this knowledge comes from the famous Surgical Papyrus, discovered by archeologist Edwin Smith [6], and which was written around 1.600 BC in Egypt. It contains the first known descriptions of cranial sutures, the external brain surface, brain liquor (CSF) and intracranial pulsation. Its author describes further 30 clincal cases of head and spine trauma, noting how the several brain injuries were associated to changes in the function of other parts of the body, especially in the lower limbs, such as hemiplegic contractures, paralysis, miction and ejaculation and priapism, due to trauma inflicted to the spinal medula.
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Skull trepanning carried out in South Americal (Inca site) |
A segment of Edwin Smith's Surgical Papyrus |
In our culture, Alcmaeon of Croton (5th century B.C) was possibly the first one to put in the brain the site of sensations. According to him, the optic nerves, supposed to be hollow, carried the information to the brain, where each sensory modality had its own localization.
During the fifth century B.C., Democritus, Diogenes, Plato and Theophrastus also indicated the brain as the seat of the body’s activities. Also among the Greeks, Herophilus (335-280 B.C.) dissected and wrote about the brain, being the first one to describe its cavities, the cerebral ventricles, which he associated with mental functions. This idea, as we shall see, would become very important in the “neurophysiology” of the forthcoming centuries.
Hippocrates (460-400 B.C.) who wrote a lot about brain’s diseases, stated that “Men ought to know that from the brain and from the brain only arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, grieves and tears”.
This is an amazing and forward looking statement,
so modern as any neuroscientist could make today. It is surprising to know, therefore, that philosophers and physicians
who came after Hippocrates, for many centuries thereafter, could make such a notable regression, by displacing
the seat of mind to the heart, as we will see below.
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Aristotle was not the first to erroneously generalize a very old notion among all kinds of antique civilizations, that the seat of emotions was the heart. Even today we are still influenced by this, such as when we refer to a heart as the symbol of love, or when we say that we got a "broken heart", or we have a "heavy heart", or still when we say that we love something with our very hearts. "Knowing by heart", such as when we memorize something, has the same origin. All this probably comes from the fact that the sympathetic branch of the autonomous nervous system is activated during strong emotions, causing a perceptible increase in heart rate and force of contractions. The temporal association of effect to its cause in its peripheral expression has led to the erroneous interpretation, which the natural philosophers tried to "explain" in scientific terms.
Anyhow, the famous Roman physician Galen (130-200) rejected Aristotles’ ideas, arguing that there were no sense in believing that the brain could cool the passions of heart. Galen dissected a lot (the animal of choice was the ox) and paid more attention to the meninges and cerebral ventricles than to the brain itself. In those days, working with unfixed material, it is only natural that the ventricles would call more attention than the brain, that would resemble an amorphous paste.
Galen
For Galen, the nutrients absorbed in the guts went to the liver, where the natural spirit was formed. This spirit was taken to the heart and, in the left ventricle, was changed into a vital spirit. The vital spirit, going through the carotid arteries, would reach the rete mirabile, a net of vessels localized in the base of the skull. There, it was blended with the inspired air, forming the animal spirit, that was stored in the cerebral ventricles, from where it could reach the rest of the brain. The animal spirit, a product of the mixture of a liquid and the air, was considered as the essence of life and the source of intellectual skills. When necessary, it could travel along the hollow nerves, eliciting movements or mediating sensations.
According to Galen, the substance refined in the rete mirabile would produce a certain amount of refuse, part of which was gaseous, the other part being liquid. The gaseous part escaped through the bone sutures and air sinuses of the skull, and its passage was not perceived by the senses. The liquid part leaked from the anterior ventricles to the openings of the cribiform plate of the ethmoid bones or, yet, from the third ventricle through the pituitary fossa. From there, it could reach the nasal cavity to be discharged as plhegm, or mucus.
Brain Ventricles and the Concept of Mind
Nemesius (circa 320), bishop of Emesa, a city in Syria, embraced Galen’s ideas and based in the cerebral ventricles the intellectual faculties. In his book “On the Nature of Man”, a treatise of physiology modeled on Greek medicine, it is said that the soul could not be localized, but the functions of the mind could. The cerebral ventricles were supposed to be responsible for mental operations, from sensation to memorization. The first pair of ventricles were the seat of the “common senses”. They would make the analysis of the information originated in the sense organs. The resultant images were carried to the middle ventricle, the seat of reason, thinking and wisdom. Then came into action the last ventricle, the seat of memory. Up to the Middle Age, the figures depicting the brain would show the ventricles with great detail.
The idea that spirits wandered in the ventricles, favored by the Church, prevailed up to the Renaissance. In a book published in the thirteenth century, named “On the Properties of Things”, a compilation made by Bartholomew the Englishman, it is stated that “the anterior cavity is soft and moist in order to facilitate association of sensual perceptions and imagination. The middle cell must also be warm, since thinking is a process of separation of pure from impure, comparable to digestion, and heat is known to be the main factor in digestion. The posterior cell, however, is a place for cold storage in which a cool and dry atmosphere must allow for the stocking of goods. That is why the cerebellum is harder, i.e. less medullary and airy, than the rest of the brain”.
Leonardo da Vinci
Therefore, for many centuries, three
ventricles were described, and the lateral ventricles were seen as only one. Leonardo Da Vinci (1472-1519) who
was a customary dissector, depicts in his illustrations the two lateral ventricles and not a single one. Da Vinci
was convinced that the senses should be localized in the middle ventricle (third ventricle), because to its neighboring
come together many of the cranial nerves.
 Brain ventricles, as drawn by Leonardo da Vinci |
 The cerebral ventricles, as depicted in Hieronymus Brunschwig’s book, published in 1525. Note that vision, taste, smell and hearing were connected to the anterior ventricle.. |
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During the seventeenth century, spirits still commanded behavior. At that time Rene Descartes (1596-1650) had chosen the pineal body, not properly as the seat of the soul, but as the place of its activity. The pineal was picked because it is a single organ, unlike the other brain structures, that come in pairs. Descartes’ neurophysiology was independent of neuroanatomy, which he deliberately ignored. It was based in the animal spirits, pores and ways by means of which they flew to exert their actions. According to him, the “most active and quickest particles of the blood” were taken by the arteries from the heart to the brain, where they were transformed in a very subtle air or wind, a very pure and active flame: the “animal spirits” [5]. The arteries were supposed to come together around the gland localized at the center of the brain: the pineal.
Descartes presumed that filaments in the nerves (supposed to be tubes) could move little valvules, opening pores that would allow the flowing or the animal spirits. A stimulus in the skin, for example, would move those filaments, inducing a contraction as a reflex response. Starting in the brain, the animal spirits wold travel along the nerves up to the muscles, inflating them to cause movements. That would be the mechanism for voluntary acts.
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A reflex response according to Descartes’ physiology. The fire elicits movement of animal spirits in hollow nerves. The movement opens pores in the ventricle (F), letting flow spirits that will inflate the muscles of the leg, that moves away from the heat. |
A drawing from the book by Rene Descartes, De Homine, published in 1662. Visual information is taken to the brain by hollow optic nerves. From there, it reaches the Pineal body (H), which regulates the flowing of animal spirits into the nerves. The spirits will go to the muscles of the arm, to produce motion. |
External stimuli should open pores in the brain and the spirits would be carried to the pineal gland, which had in its surface a complete sensorial and motor map. The will was under pineal’s control, which could manage the flow of the animal spirits into different nerves.
  Sleep and wajing, according to Descartes (1662), would depend on the flow of animal spirits in the brain, which were regulated by the pineal gland (H). In the upper drawing, there is a small flow of spirits and the brain is is an "flacid state" during sleep. The lower drawing represents the state of awakeness, when the greater inflow of spirits distents brain matter. |
Diversity of sensations would be explained by the manner that the pores were open. A strong stimulus, for example, would cause pain. A uniform stimulation of many fibers in the skin would be felt as a smooth surface. The irregular stimulation would cause a feeling of a rough surface.
According to Descartes, the animal
spirits could dilate the brain, just as the wind acts on the sails of a boat. This action would wake up the brain
and allow reception of sensorial information. The absence or small intensity of the animal spirits would
induce sleep and dreams. The animal spirits were also the base for his theory of a cerebral localization of movements
and sensations. Each person’s distinct temperament and natural skills should be due to differences in number, size,
shape and movement of the animal spirits.
Bioelectricity and
the Neuronal Dogma
The belief in animal spirits travelling
along the nerves, born among the Greeks, remained current up to the eighteen century, when the electric nature
of nerve conduction was verified. For that, it was important the work of Luigi Galvani (1737-1798) and, in the
following century, the work of Emil du Bois-Reymond (1818-1896). Du Bois-Reymond made his studies on nervous transmission
in the 1840 decade and in the 1870 decade he proposed that the effector organs were excited by the nerves via currents
or by means of chemical substances liberated by the nerve endings.
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Luigi Galvani |
Emil Du Bois-Reymond |
The nineteenth century brought the acknowledgment that brain’s tissue
was important for nervous functions. Theodor Schwann (1810-1882), who described the myelin sheath, was the first
to propose that the body is made of individual cells. His cellular theory was accepted for the whole body, with
the exception of the nervous system, that was supposed to be made of cells whose branches formed a continuous net.
Only after the discovery of the staining
method of silver impregnation of nervous elements (Golgi method) an accurate analysis was possible, introducing
the works of Santiago Ramon y Cajal (1852-1934) who affirmed, in 1889, that the nervous cells were isolated units.
Wilhelm von Waldeyer (1836-1921), in 1891, coined the term “neuron” to designate the anatomical and functional
unit of the nervous tissue. Finally, spaces in the junctions between nervous cells or between nervous and muscular
cells were described by Charles Scott Sherrington (1857-1952). Sherrington gave these structures the name
of “synapses”.
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 Dr. Ramon Moreira Cosenza, MD, PhD |
Dr. Ramon Cosenza is a physician, with a doctorate
in anatomy, who is a former professor of the Federal University of Minas Gerais, Brazil. He teaches and consults
in clinical neuropsychology in Belo Horizonte. Dr. Cosenza is the author of numerous scientific papers in his research
and clinical areas and has authored a book on the Fundamentals of Neuroanatomy, published in 1998 by Guanabara-Koogan.
To contat the author:
Email: cosenzar@brfree.com.br
