Brain Activities Responding to Acupuncture at ST-36 (Zusanli) in Healthy Subjects: A Systematic Review and Meta-Analysis of Task-Based fMRI Studies

# Acupuncture at ST-36: What Neuroscience Reveals About Its Effects on the Brain

A recent high-quality scientific study investigated how acupuncture at ST-36 (known as "Zusanli") affects the brain in healthy individuals, using functional magnetic resonance imaging technology. This research represents an important advance in our scientific understanding of the neurological mechanisms of acupuncture, an ancient practice of traditional Chinese medicine that has been gaining increasing recognition in modern medicine.

ST-36 is one of the most important and widely used acupuncture points in clinical practice. Located in the leg, approximately four finger-widths below the inferior border of the patella and one finger-width lateral to the anterior border of the tibia, this point is traditionally used to strengthen the spleen and stomach, regulate the meridians, and improve overall body vitality. In contemporary medicine, acupuncture at this point has been applied for pain management, improvement of cognitive function, cerebral circulation, and regulation of gastrointestinal disorders.

The primary objective of this research was to identify and precisely map which brain regions are activated when ST-36 is stimulated by acupuncture in healthy individuals. The researchers conducted a systematic review and meta-analysis, considered the gold standard of scientific research, pooling data from sixteen independent studies that used functional magnetic resonance imaging to observe brain activity during acupuncture sessions. This methodology allows combining results from multiple studies, increasing the reliability of conclusions and providing a more comprehensive view of the neurological effects of acupuncture.

In total, data from 401 healthy right-handed participants were analyzed, including 199 men and 202 women, from studies conducted in different countries including the United States, China, Korea, and Germany. The researchers used an advanced technique called seed-based d mapping with permutation of subject images, which allows identifying with high statistical precision which brain areas show greater activity during acupuncture stimulation. Additionally, subgroup analyses were performed to compare the effects of traditional manual acupuncture with electroacupuncture, as well as analyses to understand how needle retention time influences brain activity.

The results revealed that acupuncture at ST-36 consistently activates three main brain regions. The first is the opercular part of the right inferior frontal gyrus, an area involved in language processing and communication. The second activated region is the left superior temporal gyrus, fundamental for auditory processing and language comprehension. The third area corresponds to the right median cingulate gyrus, an important region for emotional processing and mood regulation.

Interestingly, the researchers found that needle retention time during the acupuncture session has a positive correlation with activation of the left olfactory cortex, suggesting that longer sessions may have specific neurological effects related to olfactory processing.

The subgroup analyses revealed important differences between stimulation modalities. Electroacupuncture, which combines traditional needles with low-intensity electrical stimulation, was shown to activate more extensive brain areas compared to traditional manual acupuncture. Specifically, electroacupuncture activated additional regions such as the left medial orbital superior frontal gyrus, right superior temporal gyrus, and left anterior thalamic projections. This finding suggests that different acupuncture techniques may have distinct neurological mechanisms, which has important implications for treatment personalization.

To better understand the functional significance of these brain activations, the researchers mapped the identified regions onto large-scale neural networks. The results showed that the areas activated by acupuncture at ST-36 belong primarily to the auditory network, anterior salience network, and posterior salience network. Using functional decoding techniques, it was possible to determine that these regions are associated with pain processing, secondary somatosensory stimulation, auditory and speech processing, and mood regulation. These findings provide a solid neurological basis for the therapeutic effects traditionally attributed to acupuncture at ST-36.

The clinical implications of these findings are significant for both patients and healthcare providers. For patients considering acupuncture as a therapeutic option, this study provides robust scientific evidence that acupuncture produces measurable and specific neurological effects in the brain. This is particularly relevant for the treatment of pain-related conditions, language disorders, and mood disturbances — areas where the identified brain regions play crucial roles. The finding that different acupuncture techniques activate different neural patterns also suggests that treatments can be optimized according to the specific needs of each patient.

For healthcare providers, these results offer valuable insights into the mechanisms of action of acupuncture, aiding evidence-based clinical decision-making. The identification of specific neural networks activated by acupuncture may help explain why this therapy is effective for certain conditions and guide the development of more precise treatment protocols. Furthermore, the understanding that needle retention time influences brain activity may lead to optimizations in treatment parameters.

It is important to acknowledge the limitations of this study for appropriate interpretation of the results. The relatively small number of included studies and total participants represents a methodological limitation. In addition, the research could not adequately assess the effects of the deqi sensation — that specific sensation of heaviness, tingling, or propagation that patients frequently report during acupuncture and which is considered fundamental to therapeutic efficacy in traditional Chinese medicine. The lack of standardized tools to quantify this sensation across the different studies made a more precise analysis of this aspect difficult.

Another important consideration is that the included studies were conducted over an extensive period during which neuroimaging techniques and analysis software evolved significantly, which may have introduced variability in the results. Additionally, although the study focused on healthy individuals to establish the basic neurological effects of acupuncture, the results may differ in populations with specific clinical conditions.

In conclusion, this study represents an important milestone in the scientific understanding of the neurological mechanisms of acupuncture. The results demonstrate that acupuncture at ST-36 produces consistent and specific brain activations in regions associated with pain processing, language, and emotional regulation. These findings not only scientifically validate the neurological effects of acupuncture but also open pathways for more precise and personalized clinical applications. For patients and professionals interested