Aristotle and the Brain

Aristotle's Contemporaries on the Brain

Alcmaeon

Alcmaeon of Croton was likely the first to practice dissection, which allowed him to find the channels (poroi) that connect the brain with sensory organs. The fact that some concepts from Alcmaeon's epistemology can be found in Aristotelian thought regarding the issue of relating the reality of experience, knowledge, and techne is not surprising. Alcmaeon, in contrast to Aristotle, believed that the brain served as the hub of human perception and thought. He is the first person on record to take the stance. In his dissection he discovered that the optic nerves “came together behind the forehead” and led to the brain, which is why he theorized the eyes moved together.

Democritus

Democritus, as we know, believed in atoms. The lightest, most spherical, and swiftest traveling atoms make up the psyche (soul, mind, and vital essence). Although the psychic atoms are spread out among the other atoms throughout the body, the brain has a far higher concentration of them. Slightly cruder atoms are concentrated in the heart, making it the seat of emotion, while even cruder ones are concentrated in the liver, making it the seat of lust and appetite. This trichotomy also appears in Plato's work.

Empedocles

Empedocles is the only one I mention who did not agree that the brain was the hegemon. Empedocles regarded blood as highly important and believed that it was the source of all sensibility and thought. He justified this by saying that blood is composed more evenly of a combination of the four elements (fluidity - water, heat – fire, density – earth, and movement – air) than the rest of our bodies which makes it suited for cognition and sense perception. This, however, does not make much sense to many modern and ancient readers.

Aristotle and The Body

Four Qualities → Hot, Cold, Dry, and Moist were coupled based on the principle of opposites. They also combine based on the principle of non-contradiction, so there are four combinations: hot-dry, hot-moist, cold-dry, and cold-moist. The combinations form things such as Blood, which is hot-moist, and Bone, which is cold-dry. The combination of the elements form the simple and uniform parts of the body. These uniform parts can be divided into smaller parts. Non-uniform parts of the body are made up of uniform parts combined, and they are the more complicated parts of the body. The heart is not uniform or non-uniform, and it bridges the gap between the different types of body parts.

The Senses

Smells arise from fire, which is hot, so the brain being so close to the nose allows smells to be cooled. The eyes are associated with water, and the brain is the “moistest and coldest part of the body,” so the eyes are linked to them. Touch and Taste are connected to the earth, which is why the hands are closer to the heart than the brain. Aristotle said that touch and taste were “clearly connected to the heart.” Hearing is associated with Air, and the Ears are on the sides of the head to hear from all directions. He said that other animals can hear and don’t have ears on their heads, so the ears being close to the brain does not mean the brain Is the center of sensation. The brain region also contains very pure blood, so sensation can be more precise.

The Heart

Aristotle believed that the heart was the center of sensation and movement in the body. During anatomical dissections, he observed that the main “sensors” (the eyes, ears, hands, nose, and tongue) were connected to the heart via blood vessels. He used that as justification that the senses were felt in the heart.

Aristotle claimed that the Finest and purest blood was found in the heart and that the heart was where heat came from/was generated in the body. Humans had the hottest and richest hearts, which is why we are so smart/different from other animals. This heat was critical, but needed to be counterbalanced.

The Brain

Aristotle claimed that the Brain is cold, which counterbalanced the heart. Men had the “largest and moistest” brains for animals our size, which allowed us to be intelligent as our intelligence is reliant on our brains being able to cool our hearts.

Aristotle believed that the smaller vessels/capillaries in the brain would allow it to be cooled more effectively. They were “thin, pure and easily cooled,” and their size allowed for evaporation. Looking at the image to the left, you can see that the vessels are much smaller in the brain than in the neck, which explains his observation.

Aristotle boiled the brain and observed once the water evaporates the brain is hard, so he believed that “hard earth” was left. According to his system earth and water are cold, so the brain is cold and moist

How did Aristotle Justify his Theory?

1. He believed that all Animals have hearts, but not all have brains.

While this is not necessarily correct, it is logical that he believed this. Looking at something like an earthworm, they do not have a brain, per say. They have neurons/axons, but no brain. However, they have a vascular system that looks much more like ours.

2. The heart changes when emotion is felt, but the brain does not.

This is not true empirically, but subjectively it makes sense that he believed this. When we are nervous, we can feel our hearts beating fast, but we do not feel the chemical processes in our brain that cause that. We feel feelings in our chests or stomachs, not in our heads. This is because the brain causes different physiological effects, but just by thinking about what we feel, this is not obvious.

3. The brain does not feel pain.

When the brain is cut in a live animal, they display no pain. If the heart is injured, it is felt. This would logically lead to the conclusion that the heart is more important than the brain for sensing pain. This is actually because the brain has no pain sensors, but the heart does. The brain being harmed does not cause physical pain, but it still is where pain is processed.

4. The heart is in a central location, and the brain is far from everything. Again, this is somewhat logical. The heart is in the middle of the body and has visible vessels connecting it to every part of the body. The brain is connected to everything by nerves, but these are not always as easy to see and it is not in the middle of the body

His main oversight was the fact that he ignored the nerve connections to the brain that were clearly visible, such as the optic nerve. As we discussed in the section on senses, Aristotle managed to explain away all of those connections.

Why Was Aristotle so wrong?

It is puzzling why Aristotle made such an astonishing error and had such a different take than Alcmaeon, the Hippocratic doctors, and most importantly from his teacher Plato. He did not disregard the brain as much as is frequently stated. Aristotle's understanding of brain function was supported by anatomical, physiological, comparative, embryological, and introspective evidence. But a crucial approach was missing.

This was the clinical approach, and the lack of investigation of people brain-damage. Alemaeon and Hippocrates were two physicians who fought for the primacy of the brain. Both had provided purely clinical data to back up their claims. Aristotle in this case seems to have come to his conclusion first and molded the available evidence to fit his theory, even when it runs counter to his claims.

Museum at Alexandria

While Aristotle's view might have been wrong, he helped push further developments in the study of the brain. Very broadly, his dissection and study of biology encouraged others to do the same. But also on a very specific level, he played several important roles in the founding of the Museum at Alexandria. The museum was founded by Ptolemy I, ruler of Egypt and one of Alexander the Great’s generals. He, along with Alexander, was a pupil of Aristotle. Demetrius and Strato, who were students of Theophrastus, the successor of Aristotle at his school the Lyceum, were brought to Alexandria by Ptolemy to help him set up the museum. Even the library’s collection is believed to have been brought by Demetrius from Aristotle's own collection.

It was there, at a museum created by Aristotle's pupils and stocked with his collection, that Herophilus and Erasistratus began systematically studying the structure of the human body and its nervous system.

The primary explanation of the extraordinary spike in interest in anatomy in second-century Alexandria was that it was the first time and place where systematic and open dissection of the human body was possible. Only animals had previously been used for anatomical dissections. The deceased human body was revered (and feared) in ancient Greece, making its dissection virtually impossible. What set Alexandria apart from the rest? A few elements appear to have combined. One of them was that Herophilus and Erasistratus had the full backing of a totalitarian government determined to glorify itself through the accomplishments of its scientists. The Ptolemys arrived in a distant land as absolute tyrants with little restraints.

A second aspect must have been that dissection of the human body for the sake of mummification had been conducted in Egypt for generations, and thus the general cultural background of Egypt probably contributed to the possibility of human dissection. However, the social divide between the Greeks in Alexandria and the locals around them appears to have been very wide, making it extremely improbable that the Greek anatomists had any interactions with the Egyptian embalmers. Another contributing element might have been the evolving philosophical perspectives on death and the human body that were becoming more prevalent at the time. After all, according to Aristotle, the body is nothing more than a mere frame without sensation or rights after death.

Aristotle's Influence After Death

Many of his ideas were still believed for a long time after his death. The idea that the heart was hotter than the rest of the body was believed until 1680 when it was actually measured by a thermometer.

Aristotle believed that men had bigger brains than women, which stuck around for way too long. His belief that the heart was very important to cognition caused a lot of people to believe it had more of an influence than it did, well into the renaissance.

As late as 1990, there were papers positing that the brain regulates temperature. This paper believed it was a refrigerator, not a radiator they believed that the brain developed evolutionarily as a refrigerator as we became bipeds. This is not in line with current scientific thought, but it shows how recently his ideas were being examined.

On the other hand, Galen was very dismissive of Aristotle’s ideas in the second century. He simplified Aristotle’s beliefs, saying that he believed that the brain was simply cold and wet.

Current Thought

We now know that the Brain is the center of thought and feelings. The brain is made up of neurons, which send electrical currents (Action potentials). These trigger the release of chemicals (neurotransmitters), that end up creating our thoughts/feelings. These processes control everything we think and experience.

The brain does regulate temperature in the body by keeping homeostasis, but it does not cool the body itself. Instead, it will trigger things like sweating or shivering. Additionally, we know that blood does not actually enter the brain because of the blood brain barrier, so Aristotle was definitely wrong on that front.

Bibliography

Aristotle. The Works of Aristotle. Clarendon Press, 1971.

This is our primary source on Aristotle’s beliefs about the brain. It allowed us to have as close to first-hand knowledge of his ideas as possible. We learned about how he believed the body was made up of different elements and qualities, along with uniform and non-uniform parts. Aristotle also explains how the senses are not connected to the brain/mostly on the head because the brain is in charge of perception, but because of other reasons.

CLARKE, EDWIN, and JERRY STANNARD. “Aristotle on the Anatomy of the Brain.” Journal of the History of Medicine and Allied Sciences, XVIII, no. 2, 1963, pp. 130–148., https://doi.org/10.1093/jhmas/xviii.2.130.

This source helped us understand what exactly Aristotle meant In his our primary sources. It related his Ideas to other theories of his that we did not necessarily know from his writings on the brain. This source also explained how Aristotle came to some of his conclusions, especially the wrong ones. For example, Aristotle dissected a number of cold blooded animals, which could/likely did lead him astray.

Gross, Charles G. “Aristotle on the Brain.” The Neuroscientist, vol. 1, no. 4, 1995, pp. 245–250., https://doi.org/10.1177/107385849500100408.

This was an incredibly helpful paper that explained a lot of context for some of Aristotle’s theories. It went over the beliefs of Alcmaeon and Hippocratic doctors, to name a few. He then explained Aristotle’s views on the brain and the heart, as well as the legacy of his theories. One of the most helpful parts of this paper was a chart that explained the differences between the heart and the brain that Aristotle used to justify his ideas. This chart was very helpful in organizing/further understanding how Aristotle came to the conclusions he did.

Oleksowicz, Michal. “Aristotle on the Heart and Brain.” Academia.edu, 8 June 2018, https://www.academia.edu/36807055/ARISTOTLE_ON_THE_HEART_AND_BRAIN.

This paper went in depth about what/how Aristotle understood the human body worked. It had a section on the brain and one on the heart. It also spoke about the implications of the Aristotelian view of living beings and Aristotelian methodology in Biology. This paper had a lot about how Aristotle believed that heat was a very important part of the body and how the heart was the center of that, which is not something many of our other papers focused on. Oleksowicz discussed the methodology of Aristotle’s research and highlighted how and why he came to the conclusions he did, while also pointing out some flaws in his methodology.

Longo O. (1996). Hot heads and cold brains. Aristotle, Galen and the "radiator theory". Physis; rivista internazionale di storia della scienza, 33(1-3), 259–266.

This paper examines Aristotle’s theory of the brain as a radiator and compares it to Falk's and Fialkowski's (1990) paper. This paper discusses the similarities and differences, which we found very interesting. It was surprising to us (and especially to Elly as a neuroscience major) that people recently proposed that the brain was a large factor in temperature control for the body. The author also explained the main difference between the theories is that Aristotle believed that the brain was an organ for cooling the body/heart's heat, while the 1990 theory proposed that the human brain developed starting as a refrigerator of itself.

Holloway, Ralph L. “Falk's Radiator Hypothesis.” Behavioral and Brain Sciences, vol. 13, no. 2, 1990, pp. 360–360., doi:10.1017/S0140525X00079139.

This paper was about a theory presented in 1990. This paper hypothesized that the brain had increased in size quickly due to the changing needs of a newly bipedal species. The authors believed that the brain's vascular system was important for releasing heat, especially for bipeds. This led to a quick increase in brain size in order to release heat when we became bipeds. This was very interesting to us because we were explaining how far-fetched Aristotle’s ideas were in antiquity, but we also found this paper that argues similar things. This theory is not widely accepted/respected, but it was a real paper from 32 years ago.

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