天美传媒

Acupuncture; Neuroimaging; Pain modulation; Functional MRI; PET; Endogenous opioids; Pain pathways; Central nervous system; Chronic pain; Analgesia; Brain activation; Descending inhibition; Nociception; Traditional Chinese medicine

Introduction

Pain, especially chronic pain, is a pervasive health concern affecting millions globally. While pharmacological therapies dominate pain management, their limitations, including side effects and dependence risks, have prompted the exploration of non-pharmacologic modalities. Acupuncture, with roots in ancient Chinese medicine, has gained considerable acceptance in integrative and mainstream medical practices for its perceived analgesic benefits. Scientific interest in acupuncture’s mechanisms has led to the application of neuroimaging technologies, such as fMRI and PET, to visualize changes in brain activity in response to acupuncture. These studies aim to bridge traditional practices with neurobiological understanding, revealing how acupuncture may influence both peripheral and central components of pain processing. This article synthesizes neuroimaging evidence to elucidate how acupuncture modulates pain pathways. By identifying consistent neural patterns and mechanistic pathways, the clinical role of acupuncture in pain management can be better defined and optimized [1-3].

Description

Acupuncture and its traditional foundation

Acupuncture involves the insertion of thin needles at specific anatomical points known as acupoints. Traditionally, this practice is believed to balance the flow of Qi (vital energy) through meridians. In Western medicine, acupuncture is often explained through neurophysiological responses involving sensory nerves, spinal cord modulation, and brain activity. The types of acupuncture include manual acupuncture, electroacupuncture (EA), auricular acupuncture, and laser acupuncture. The analgesic effects are attributed to peripheral stimulation of A-delta and C-fibers, which send signals to the spinal cord and brainstem, initiating pain modulation [4].

Pain pathways in the central nervous system

Pain perception involves a complex network of brain regions known as the "pain matrix," including:

• Thalamus – relay center for nociceptive signals.

• Somatosensory cortex (S1 and S2) – processes pain localization and intensity.

• Insula – associated with pain affect and interoception.

• ACC – involved in the emotional component of pain.

• Prefrontal cortex (PFC) – integrates cognitive and evaluative aspects.

• PAG and rostroventromedial medulla (RVM) – major centers for descending pain inhibition [5].

Neuroimaging has been instrumental in mapping the response of these areas during and after acupuncture stimulation.

Neuroimaging techniques in acupuncture research

1. Functional MRI (fMRI): Measures changes in blood oxygen level-dependent (BOLD) signals during acupuncture, indicating neural activity.

2. Positron Emission Tomography (PET): Tracks metabolic changes and neurotransmitter binding, particularly opioid receptor activity.

3. Diffusion Tensor Imaging (DTI): Assesses structural brain connectivity and white matter changes.

4. Magnetoencephalography (MEG): Measures magnetic fields generated by neuronal activity for high temporal resolution studies [6].

Discussion

Findings from functional mri studies

Numerous fMRI studies have shown that acupuncture leads to activation and deactivation in brain regions associated with the sensory, affective, and cognitive components of pain [7]. In patients with chronic pain, acupuncture has been found to:

• Reduce activation in the somatosensory cortex, indicating decreased pain perception.

• Enhance activity in the PAG, ACC, and PFC, contributing to increased endogenous inhibition.

• Alter connectivity within the default mode network (DMN), reducing pain-related rumination and self-referential thought.

For example, one study demonstrated that electroacupuncture at LI4 (Hegu) reduced BOLD signals in the thalamus and insula while increasing activity in the medial prefrontal cortex, correlating with reported pain relief.

Evidence from PET imaging

PET imaging has provided compelling evidence that acupuncture induces the release of endogenous opioids. Studies using radiolabeled ligands for mu-opioid receptors have shown increased binding potential in key pain modulatory areas, particularly:

• Anterior cingulate cortex

• Nucleus accumbens

• Amygdala

• Thalamus

This opioid-mediated mechanism explains the delayed and sustained analgesic effects observed after acupuncture treatment.

Impact on the descending pain modulatory system

Acupuncture appears to strongly influence the descending pain modulatory system (DPMS), a critical pathway for pain inhibition. Activation of the PAG–RVM–spinal cord axis results in the suppression of nociceptive transmission. Electroacupuncture has shown robust activation of the PAG, suggesting that acupuncture enhances the brain’s natural ability to dampen pain signals [8]. Additionally, increased activity in the dorsolateral prefrontal cortex (DLPFC) during acupuncture may support cognitive modulation and placebo-related analgesia, further implicating top-down pain control mechanisms.

Chronic pain conditions and acupuncture response

Neuroimaging studies in patients with:

• Low back pain

• Osteoarthritis

• Fibromyalgia

• Migraine

Have shown condition-specific changes in brain function following acupuncture. For instance, in fibromyalgia patients, acupuncture normalized abnormal thalamic connectivity and reduced hypersensitivity, correlating with symptom improvement. Longitudinal studies have revealed that regular acupuncture treatments induce structural brain changes, including increased gray matter volume in the insula and PFC. These neuroplastic adaptations may underlie acupuncture’s long-term benefits [9].

Sham-controlled and placebo studies

One challenge in acupuncture research is the differentiation between specific and non-specific effects. Sham acupuncture (superficial needling or needling at non-acupoints) often produces similar subjective pain relief, raising questions about the specificity of neural responses. However, neuroimaging has shown that true acupuncture results in distinct patterns of brain activation, particularly in deeper limbic and brainstem structures. Sham acupuncture may activate sensorimotor areas, suggesting that tactile stimulation alone cannot account for the full analgesic effects.

Clinical relevance and personalization of treatment

Understanding neural signatures associated with acupuncture response may help tailor treatments. For example, individuals with greater baseline connectivity in the DMN may be more responsive to acupuncture-induced analgesia. Such findings open the door to personalized pain management using neuroimaging biomarkers. Additionally, combining acupuncture with cognitive-behavioral therapies or pharmacological agents may synergistically enhance outcomes, particularly in treatment-resistant chronic pain syndromes [10].

Conclusion

Neuroimaging studies have significantly advanced our understanding of how acupuncture modulates the central nervous system to achieve pain relief. By influencing multiple regions involved in sensory, emotional, and cognitive pain processing, acupuncture offers a complex and multi-targeted approach to pain modulation. Functional and molecular imaging reveals that acupuncture not only alters neural activity but also engages endogenous opioid systems and promotes neuroplastic changes, particularly with repeated treatments. These findings validate acupuncture’s role as a credible, evidence-based intervention in the management of chronic pain. Future research should focus on refining neuroimaging methodologies, identifying patient-specific predictors of response, and integrating acupuncture into personalized, multimodal pain management strategies. As imaging technologies continue to evolve, they will play a pivotal role in demystifying acupuncture and solidifying its place in modern medicine.