The Brain and the World: Pulp Appendix - History of the Brain II

The human brain is a yellowish greyish pulp overspread with small capillaries. You can hold it in one hand like a ball. It is not as soft as you would imagine, and not as light as you might think. You can cut it open, studying the fine structures of white and grey foldings in recognizable patterns. You can fry it with vinegar and garlic, and it will taste like vinegar and garlic.

What does it do?

Aristotle thought the function of the brain was to cool the blood. It is easy to see how this conclusion could be reached in an ancient world struggling with the interpretations of physiology. The pounding of the heart as an emotional response would easily prompt the idea that the heart was the seat of the soul. Blood was supposedly warmed in the heart, flowing through blood vessels to heat other organs. With the abundance of vessels in the skull and capillaries spreading out like a delta floodplain around the brain, it must have been an obvious assumption that blood could be cooled in this gooey mass, like hot water flowing over cold rocks.

Other physicians interpreted the anatomy differently. Based on the anatomical observations that the optic nerves connect the eyes with the brain, Alcmaeon of Croton recognized the brain as the organ of perception. Alcmaeon was also the first to identify the eustachian tubes linking the inner ear to the nasal cavity. These observations of pores, tunnels, chambers and canals of the skull must have led him to the obvious assumption that the brain is the centre of the senses.

In Alexandria, Herophilos and Erasistratus mapped the nerves leading from the brain to the muscles and discovered the difference between sensory and motor nerves. Herophilus in an apparently arbitrary insight located the soul to the fourth ventricle of the brain.

No text by Alcmaion or by Erasistratus exists in its entirety, but they are quoted by another important physician, the roman Galen. His teachings on human physiology and humorism would influence Western thinking for centuries. While working as a physician to the gladiators at Pergamon, like the Egyptian battle surgeon milleniums before him, Galen recognized that a blow to the head would cause the gladiator to pass out. He concluded that the brain must be the seat of consciousness. Although an admirer of Aristotle, he opposed the idea of the brain as a cooling organ secondary to the emotions of the heart. And although schooled in the Aristotelian principle of recognizing only what could be experienced by the senses, Galen did publish a lot of unsubstantiated speculations. Fascinated by the rete mirabili, a complex of arteries and veins covering the brain at the basis of the skull, he wrote “[it] is not a simple network but (looks) as if you had taken several fishermen’s nets and superimposed them. [Y]ou could not compare this network to any man-made nets, nor has it been formed from any chance material. Nature appropriated the material for this wonderful network.” He excitedly concluded that vital spirits were produced in the heart, transported by the carotid arteries to the brain, and transformed to the highest spirits of man in the rete mirabili.

Galen could easily have been proven wrong though; had he dissected gladiators instead of sheep, he would have realized that the rete mirabili is found in only some mammals, but not in humans.

The Rete Mirabili. In sheep.

Other attempts were made. Leonardo da Vinci contributed to neuroanatomy with impressive drawings, beautiful and with an unmistakably Leonardian attention to detail. Using hot wax, he casted the ventricles of the brain, producing unprecedented anatomical insight. He’s idea that three ventricles held sensation, intellect and memory respectively, was however pure speculation and guesswork.

For centuries the comprehension of the human mind was based on anatomy alone. It would require the combination of anatomy and clinical findings to localize cognitive functions and substantiate our knowledge of the brain.

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Finger S: Origins of Neuroscience: A History of Explorations Into Brain Function. Oxford University Press 1994

Porter R: The Greatest Benefit To Mankind - A Medical History of Humanity from Antiquity to the Present. HarperCollinsPublishers 1997

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Find all chapters of

The History of the Brain

here:

I: Violent beginnings

II: Pulp Appendix

III: Disappointing Anatomy

IV: Map of Darkness

V: Unuttered Language