A systematic review and coordinate-based meta-analysis of fMRI studies on acupuncture at LR 3

Acupuncture is an ancient practice of traditional Chinese medicine that, in recent decades, has gained growing recognition in Western complementary medicine. Although it is widely used for the treatment of pain, depression, anxiety, and various other conditions, the brain mechanisms by which it works are still not fully elucidated. The LR-3 acupuncture point, known as Taichong, is located on the liver meridian and is considered fundamental for regulating emotions, relieving pain, and reducing blood pressure. According to traditional Chinese medicine, this point has the ability to harmonize liver energy and improve the circulation of vital energy throughout the body.

To better understand how acupuncture works in the brain, researchers have used modern neuroimaging techniques, especially functional magnetic resonance imaging (fMRI), which allows brain activity to be observed in real time.

This study represents the first systematic meta-analysis using the SDM (Seed-based d Mapping) technique to investigate how stimulation of the LR-3 point modifies brain activation patterns in healthy individuals. The researchers carried out a comprehensive search across eight scientific databases, in both English and Chinese, collecting studies that used functional magnetic resonance imaging to examine the effects of acupuncture at the LR-3 point. Only studies with healthy adult participants were included, which analyzed the immediate effects of acupuncture on brain activity and provided precise coordinates for the activated brain regions. In the end, ten high-quality studies were selected, involving 319 right-handed healthy participants.

The methodology used rigorous statistical analyses to identify which brain regions are consistently activated during LR-3 stimulation, in addition to examining factors such as needle retention time and the type of magnetic resonance imaging examination used.

The results revealed that acupuncture at the LR-3 point consistently activates four specific brain regions: the right postcentral gyrus, the left thalamus, the left middle frontal gyrus, and the right superior frontal gyrus. The right postcentral gyrus, which is part of the primary somatosensory cortex, is responsible for processing tactile, thermal, and painful sensations of the body. Its activation suggests that acupuncture at LR-3 directly influences brain systems involved in pain perception and modulation. The thalamus, a deep brain structure that acts as a relay station for information among different brain regions, was activated, which is significant given its crucial role in both acute pain perception and emotional processing.

A particularly interesting finding was that the longer the needle retention time, the greater the activation of the right superior frontal gyrus, a brain region closely related to emotional control and stress regulation. The left middle frontal gyrus, traditionally associated with language processing and cognitive functions, also showed consistent activation, suggesting that LR-3 stimulation may influence neural networks involved in cognitive processing.

For patients and healthcare providers, these findings provide important insights into the neurobiological mechanisms of acupuncture. The activation of brain regions related to pain processing provides a scientific basis for the clinical use of acupuncture in the treatment of painful conditions. The influence on emotional regulation areas suggests that LR-3 may be especially useful in the treatment of mood disorders such as depression and anxiety, corroborating its traditional use in Chinese medicine. The fact that longer acupuncture sessions intensify the activation of emotional control areas indicates that treatment duration may be an important factor to consider in therapeutic prescription.

For providers, these results suggest that acupuncture at LR-3 does not act only locally, but promotes changes in complex neural networks that include pain, emotion, and cognitive systems. This may explain why this point is traditionally considered so versatile in the treatment of different conditions.

The mapping of activated regions to functional brain networks revealed that acupuncture at LR-3 primarily influences six neural networks: the basal ganglia network, the auditory network, the left executive control network, the posterior salience network, the right executive control network, and the sensorimotor network. These networks are involved in functions such as motor control, emotional processing, attention, and decision-making. Subgroup analysis showed that studies using functional magnetic resonance imaging during stimulation (ts-fMRI) presented results more consistent with the main analysis than studies comparing true points with sham points (rs-fMRI), suggesting that the former approach may be more accurate for detecting acupuncture's specific effects.

Some important limitations must be considered when interpreting these results. First, the number of studies included was relatively small, and some had limited participant samples. In addition, all studies were performed in healthy people, so the results may not apply directly to patients with specific diseases. Differences in acupuncture techniques, neuroimaging data processing, and experimental designs across studies may also have influenced the results.

Some studies used unilateral LR-3 stimulation, while others used bilateral stimulation, which may produce differences in brain activation patterns. Future studies with larger samples and standardized methodologies will be needed to confirm and expand these findings. Research in patients with specific conditions such as chronic pain or depression will also be valuable for better understanding the therapeutic effects of acupuncture at LR-3.

In conclusion, this study provides solid scientific evidence that acupuncture at the LR-3 point produces specific and consistent changes in brain activity in healthy people, activating regions involved in pain processing, emotional regulation, and cognitive functions. The findings offer a neurobiological basis for understanding the therapeutic effects traditionally attributed to this acupuncture point and may guide future research and clinical practice in the field.