Effects and Mechanisms of Acupuncture Based on the Principle of Meridians

Acupuncture, a millennia-old practice originating in China more than 2,000 years ago, has gained growing acceptance in the Western world as a complementary therapy. Based on the ancient "meridian theory" described in the Yellow Emperor's Classic of Internal Medicine, this therapeutic approach remains a fundamental pillar of traditional Chinese medicine for the diagnosis and treatment of various health conditions. Although many physicians trained in Western medicine still show reluctance to recommend acupuncture due to controversies about its efficacy and its poorly understood physiological mechanisms, scientific research over the last five decades has revealed fascinating neurological aspects that help explain how this therapy works in the human body.

This review study, conducted by researchers at the University of California, Los Angeles, had as its primary objective to examine and synthesize current scientific knowledge of the neurological mechanisms of acupuncture, specifically analyzing the anatomical and physiological aspects of acupuncture points and meridians. The authors carried out a comprehensive analysis of the scientific literature, reviewing findings from anatomical, physiological, and neurological research conducted over half a century. The methodology involved compiling and critically analyzing studies that investigated the anatomical structures underlying acupuncture points, the types of nerve fibers activated during treatment, and the central neurological mechanisms responsible for the observed therapeutic effects.

The principal findings revealed surprising aspects of the anatomy of acupuncture points. Contrary to initial expectations, the researchers confirmed that there are no unique or exclusive anatomical structures at acupuncture points. Instead, these points consistently correspond to locations where important neural bundles are found. For example, the pericardium meridians, widely studied for cardiovascular conditions, overlap with the deep median nerve, whereas points related to gastrointestinal processes coincide with the deep peroneal nerve.

The research demonstrated that needle stimulation, whether by manual manipulation or low-frequency electroacupuncture, has a solid neurophysiological basis for modulating the activity of peripheral and central neural pathways. Detailed anatomical studies showed that points on the face and forehead are located along trigeminal and facial nerve endings, while points on the trunk correspond to cutaneous branches of spinal nerves, each related to internal organs of the same spinal segments.

A particularly interesting finding concerns the specific types of nerve fibers activated during acupuncture. The essential sensation known as "De-Qi," described as numbness, fullness, and sometimes pain, correlates with the activation of type II nerve fibers. Japanese researchers confirmed that these fibers are sufficient to produce acupuncture analgesia in experimental models. Importantly, different conditions require activation of different types of nerve fibers.

To treat cardiovascular diseases such as hypertension and cardiac problems, acupuncturists use specific points innervated by deep somatic nerves with more myelinated fibers, whereas to treat hypotension and shock, they employ different points that may represent areas of referred pain.

The study also revealed the dynamic nature of acupuncture points. Unlike fixed anatomical structures, these points are pathophysiological entities that change their sensitivity according to alterations in body homeostasis. When internal balance is optimal, most points show no sensitivity, but they become sensitive or painful under adverse conditions. This characteristic suggests that the number of sensitive points may serve as a quantitative indicator of overall health status, with more sensitive points indicating greater homeostatic imbalance and the need for more treatment sessions.

The clinical implications of these findings are significant for both patients and healthcare professionals. For patients, understanding that acupuncture has a solid scientific basis may increase confidence in treatment and improve therapeutic adherence. The knowledge that acupuncture points correspond to real neural structures provides a rational explanation for the observed effects, which is especially important for patients who are skeptical of traditional medicine approaches. For professionals, this neurophysiological understanding enables more precise patient evaluation, making it possible to predict how many sessions will be needed and to tailor treatment according to the specific condition.

The identification of sensitive points may serve as a complementary diagnostic tool to assess overall health status and monitor response to treatment.

The study has some important limitations that must be considered. Although the correlation between acupuncture points and neural structures has been demonstrated, the exact mechanisms by which stimulation of these points produces therapeutic effects in distant organs are still not fully elucidated. Meridian theory, although clinically useful, has no directly identifiable anatomical correlate and remains a conceptual model based on empirical observations. In addition, individual variability in response to acupuncture suggests that additional factors, possibly genetic or epigenetic, may influence treatment efficacy.

The authors acknowledge that despite significant advances in the scientific understanding of acupuncture, we are still far from fully understanding all the neurophysiological mechanisms involved. Nevertheless, they emphasize the importance of keeping meridian theory in mind, since completely dismissing this traditional knowledge could result in the loss of valuable information that our current science is not yet able to explain adequately.