The Brain in Korean Medicine: The Sea of Marrow and Its Roots in the Five Organs

The brain is still, even today, one of the least understood tissues in the body — a mysterious organ whose workings modern science is only beginning to map. Korean Traditional Medicine (KTM), the traditional healing system of Korea also known as Hanbang (한방), approached it from a different direction, and gave it a name that sounds strange to modern ears: the sea of marrow. That image is not decoration. It carries a specific claim about where the brain comes from, what it depends on, and — most usefully — how to treat it when it falters.

In Summary

The Huangdi Neijing (黃帝內經) already recognized the brain as vital and directly tied to life, and named it the “sea of marrow” (수지해, 髓之海) — formed from gathered marrow.
KTM traces the brain’s formation along a pipeline: food → qi and blood → essence (精) → marrow (髓) → brain.
The essence that fills the brain has two roots, and this is the crucial point: prenatal essence (先天之精), inherited and stored by the Kidney, and acquired essence (後天之精), which the Spleen makes continuously from food.
The brain does not work alone; it expresses the sensations, emotions, and thoughts of the five organs and functions on the basis of their health.
Clinically, when brain function declines, KTM looks past the brain to the organs behind it — and treating the weakened organ can improve the brain. This view earns its place because treatment based on it actually works.

The Sea of Marrow

The Huangdi Neijing, the foundational classic thought to have been compiled around the Han dynasty, already understood the brain as a deeply important organ, directly bound up with life itself. It observed that when something goes wrong with the brain, the results are wide-ranging: disturbed emotional regulation, dizziness, ringing in the ears, altered sensation, changes in vision, weakness of the muscles. As for what the brain actually is, the Neijing called it the sea of marrow (수지해, 髓之海) — an organ formed by marrow gathering and pooling together. Much later, the Qing-dynasty physician Wang Qingren (王清任) argued that the brain’s sharp faculties and its power of memory are possible because the clearest and most refined qi (氣) in the whole body collects to form it. Ancient practitioners had also already grasped the brain and spinal cord as a single integrated system.

How the Brain Is Formed

KTM describes the making of the brain as a chain of refinement, each step distilling something more concentrated from the last:

food → qi and blood → essence (精) → marrow (髓) → brain

Food becomes qi and blood; qi and blood are stored in their most concentrated form as essence; essence is transformed into marrow; and marrow, pooling as the sea, becomes the brain.

The most important part of this picture is where the essence itself comes from, because it has two roots. There is prenatal essence (先天之精, seoncheon-ji-jeong) — the essence we are born with, inherited from our parents and stored by the Kidney. And there is acquired essence (後天之精, hucheon-ji-jeong) — the essence the Spleen produces continuously from the food and drink we take in. The Kidney is the root of the first; the Spleen is the source of the second. Together they keep the body’s reservoir of essence full, and it is from this combined essence that marrow is made and the sea of marrow is replenished. This is why, alongside the Kidney, the Spleen matters so much to the brain: without the acquired essence it draws from food, the pipeline from food to marrow has nothing to run on.

The Brain and the Five Organs

The brain receives the help of the five organs and expresses their sensations, emotions, and thoughts; it therefore exercises its abilities on the foundation of how those organs are functioning. Several are especially connected to it.

The Kidney stores essence — above all the prenatal essence — and from that stored essence makes the marrow that becomes the brain, which makes it the organ most deeply connected to the brain’s material and functional substance. The Spleen, as the source of acquired essence, keeps that reservoir replenished from daily food, and so stands just behind the Kidney in importance. The Heart, as the monarch of the organs, governs mental activity and is the place where the spirit gathers — so it bears directly on the brain. And the Liver governs the free coursing of qi (疏泄, soseol), which is involved in the very earliest stage of thought and emotion and continues to influence mental activity throughout its course; its effect on the brain is considerable.

This is not merely theoretical. In practice, when someone’s brain function is declining, KTM does not examine the brain alone. It asks which of the organs has weakened alongside it, and treats to lift that organ — improving brain function by way of its roots rather than only its surface.

Why This View Is Useful

When people say “the true substance of the mind is the brain,” I take them to mean the hardware — the physical, functional seat of the mind. In that sense the brain, in my reading, is where the mental activity of the five organs is organically linked together and where its results are recorded. KTM looks at the brain and at brain disease through the lens of the sea of marrow, and the reason this lens is worth keeping is simple and practical: when you treat on the basis of it, the results actually hold. Understanding the relationship between the brain and the Zang-fu organs is, I believe, one of the most useful ways to understand brain function at all.

In Summary

KTM calls the brain the sea of marrow — an organ distilled from food through qi, blood, essence, and marrow, and one that voices the work of the five organs rather than acting alone. Its essence has two sources above all: the prenatal essence stored by the Kidney and the acquired essence the Spleen draws from food. The Heart governs the mind, and the Liver shapes the first movement of thought and feeling. So when the brain falters, the tradition looks to the organs behind it, and treats them. It is an old picture, but a working one — and that, in the end, is why it has lasted.

This article reflects the clinical observations and teaching practice of Professor Seungho Baek, Professor of Korean Medicine at Dongguk University College of Korean Medicine, specializing in Pathology and Oncology.