What Are Meridians?
The theory of meridians is one of the core foundations of traditional Chinese medicine, originating from antiquity and still serving modern healthcare. For over two millennia, it has played a vital role in safeguarding the health of the Chinese nation.
*Huangdi Neijing* states: “Meridians are what sustain life, cause disease, enable healing, and trigger illness.” Meridians “lie hidden beneath the flesh, invisible deep inside, while superficial ones visible are merely collateral vessels.” They possess the ability to “determine life or death, treat all diseases, regulate deficiency and excess, and must remain unblocked.” Hence, acupuncture uses fine needles to “open meridians, regulate blood and qi, harmonize the flow of yin and yang, and transmit this knowledge to future generations.” Clearly, meridian theory plays a decisive role in guiding all branches of traditional Chinese medicine.
What are meridians? Where do they exist in the human body? What functions do they serve, and how are these achieved? These questions are major scientific research topics both domestically and internationally, and deeply interest the general public. Although significant progress has been made in meridian research, experimental studies and theoretical hypotheses remain in a stage of diverse theories and accumulating data. Thus, definitive scientific conclusions about meridians require long-term, arduous exploration.
Over 2,500 years ago, China produced its first medical masterpiece—the *Huangdi Neijing*. Throughout this text, a central concept runs: meridians. Meridians refer collectively to jing (main channels) and luo (collateral channels). Ancient people discovered longitudinal pathways throughout the body, named jing. They also observed branching networks off these main lines, with finer branches, termed luo. “Luo” is the overarching term for this structure.
The *Huangdi Neijing*’s understanding of meridians arose from extensive clinical observation. Evidence of these observations has gradually emerged from unearthed artifacts such as Mawangdui silk manuscripts, Zhangjiashan bamboo slips, and the Mianyang wooden mannequin with meridian models. These early texts primarily describe the meridian system and reference three ancient therapies: moxibustion, bian stone therapy (using stones for treatment), and dao yin (an ancient qigong practice). Meridians served as the pathways for these treatments.
With advances in metal smelting, metal needles—called micro-needles—were created and used for meridian therapy. The *Huangdi Neijing* consists of two volumes; one, known as *Ling Shu* or *Zhen Jing*, specifically discusses micro-needle treatment of meridians. The *Huangdi Neijing* systematically summarized meridians, adding new concepts beyond jing: luo, jingbie (extraordinary channels), jingjin (muscle channels), pibu (skin regions), and qi jing (extraordinary meridians). Together, they form the meridian system—a paramount physiological structure in ancient Chinese thought. The text also describes meridian functions: circulating qi and blood, balancing yin and yang, nourishing tendons and bones, lubricating joints, connecting zang-fu organs and exterior-interior pairs, and transmitting pathogens.
The *Huangdi Neijing*’s understanding of meridians mainly derived from long-term clinical observation, supplemented by logical reasoning and analogical descriptions. However, its conceptual framework dates back 2,500 years, posing great challenges for modern interpretation. Thus, deciphering the classical meaning of meridians through literature, experiments, and interdisciplinary research remains a critical task for TCM scholars.
Exploring Meridians Through Sensory Conduction
For over half a century, domestic and international researchers have persistently explored meridians. Initially, the question was whether ancient meridians truly existed. Some claimed they were merely blood vessels in modern anatomy, denying a distinct meridian system. Others claimed to discover physical meridians, but Chinese scholars proved these were illusions.
In the 1950s, researchers observed a strange phenomenon during acupuncture: some patients experienced a sensation traveling along the meridian pathway. This was later formally named “meridian sensory conduction.” Those capable of this phenomenon are called “meridian-sensitive individuals”—but they constitute only a small fraction of the population. The discovery challenged the notion that meridians were blood vessels, since blood vessels cannot produce such moving sensations. Additionally, researchers found lower skin resistance along meridian paths—providing preliminary evidence for meridians’ objective existence.
By the 1970s, deeper research revealed unusual characteristics of meridian sensory conduction:
• Slow speed—centimeters per second.
• Can be blocked by mechanical pressure, saline injection, or cooling.
• Can reverse direction or fail to conduct.
• Can bypass scar tissue and pass through local anesthesia zones; tends to target diseased areas.
• Along the conduction path, vascular dilation, mild edema, and measurable muscle electrical activity may occur.
• Some amputees report phantom meridian sensations at the amputation site.
These phenomena complicated our understanding: neither pure neural transmission nor blood flow alone can explain them. However, since these findings rely heavily on subjective reports, their reliability is limited. Thus, concurrent research on visible meridian phenomena and objective detection methods became crucial. This included skin hypersensitivity, pigment bands, detectable micro-acoustic waves (meridian acoustic emission), latent meridian conduction (present in over 90% of people), and other physical traits along meridians.
By the mid-1980s, meridian research received national attention, launching China’s first national-level meridian project—the “Seventh Five-Year Plan” National Key Project: “Objective Detection of the Fourteen Meridians.” Scientists no longer relied solely on subjective perception but sought scientific proof of meridian pathways. A landmark discovery was capturing gamma camera images of radioactive isotopes moving along meridian routes. Using biophysics, researchers identified meridian features: low electrical resistance, high acoustic vibration, superior sound/light/heat conduction, and isotope migration. These findings were compiled in the seminal work *Biophysics of Acupuncture and Meridians*, marking a milestone in objectively proving meridian existence.
Entering the 1990s, China launched two national-level meridian research projects: the “Eighth Five-Year Plan” and “Ninth Five-Year Plan” Meridian Climbing Programs. Research shifted from phenomenology to mechanism, focusing on three aspects: the mechanism of meridian sensory conduction, meridian-visceral relationships, and physicochemical properties of meridian lines. Several hypotheses emerged:
• Neural Theory: Meridian conduction results from neural excitation transmission between neurons.
• Body Fluid Theory: “Qi and blood” in TCM refer to bodily fluids; meridians are fluid pathways, and fluid movement stimulates nerves to produce meridian sensation.
• Energy Theory: Meridians are channels for physical energy and information transmission.