Default Mode Network as a Neural Substrate of Acupuncture: Evidence, Challenges and Strategy

Acupuncture represents one of humanity's oldest therapeutic practices, with more than 3,000 years of history in traditional Chinese medicine and currently applied worldwide. Although its neurobiological mechanisms are not yet fully understood, growing scientific evidence indicates that acupuncture promotes significant changes in brain activity. A recent study published in Frontiers in Neuroscience specifically investigated how acupuncture interacts with a fundamental brain network called the Default Mode Network (DMN), proposing a new approach to understanding the mechanisms of action of this ancient therapy.

The Default Mode Network represents a recently discovered brain system characterized by high activity at rest but which deactivates when we focus our attention on external stimuli. This network includes important brain regions such as the medial prefrontal cortex, anterior and posterior cingulate cortex, orbitofrontal cortex, inferior parietal lobe, and precuneus. What makes this network particularly interesting is that it plays a crucial role in maintaining physiological homeostasis, and its functional architecture becomes disorganized in various diseases. Previous studies have demonstrated that patients with chronic pain, depression, autism, schizophrenia, Alzheimer's disease, and other conditions show significant alterations in the function of this brain network.

This work represents a comprehensive review of the scientific literature examining the interactions between acupuncture and functional brain networks, with a special focus on the DMN. The researchers analyzed functional magnetic resonance imaging studies that investigated how different modalities of acupuncture — including manual acupuncture, electroacupuncture with different frequencies and intensities, stimulation of specific points, and treatment of healthy versus diseased patients — affect the activity and connectivity of this brain network. The main objective was to integrate existing knowledge about these mechanisms and propose a translational research strategy to better elucidate how acupuncture works in the brain.

The results revealed fascinating findings about how acupuncture modulates brain activity. Analyses of multiple studies demonstrated that acupuncture produces multidimensional brain responses, activating not only sensory areas related to the processing of the physical stimulus of the needle, but also regions involved in affective and cognitive processing. Specifically, acupuncture activates the cortical sensorimotor network, including the insula, thalamus, anterior cingulate cortex, and primary and secondary somatosensory cortices, while simultaneously deactivating the neocortical limbic-paralimbic network, which includes components of the Default Mode Network. An important finding was that DMN deactivation induced by acupuncture is more intense than that produced by placebo acupuncture or simple tactile stimulation, suggesting therapeutic specificity.

In patients with chronic low back pain, for example, acupuncture was able to reverse abnormal alterations in DMN connectivity, restoring it nearly to the levels observed in healthy individuals, with these improvements in brain connectivity correlating with the reduction in clinical pain reported by patients. Similar effects were observed in other conditions: patients with depression showed broad activation of the posterior DMN and increased connectivity between key regions after acupuncture; stroke patients showed improvement in communication between important brain areas; and individuals with Alzheimer's disease had attenuation of harmful alterations in DMN connectivity.

The clinical implications of these findings are promising for both patients and healthcare providers. For patients suffering from chronic conditions such as pain, depression, or stroke sequelae, these results provide objective scientific evidence that acupuncture produces measurable changes in brain function that correlate with symptom improvement. This can help demystify acupuncture and increase patient confidence in treatment. For healthcare providers, understanding that acupuncture specifically modulates fundamental brain networks offers a rational basis for its integration into therapeutic protocols, especially considering that different acupuncture points produce both common and specific effects in the brain.

For example, while several acupuncture points share the ability to modulate connectivity between key DMN regions, specific points such as GB-37 (related to ocular conditions) and KI-8 (related to gynecologic disorders) produce unique patterns of activation in brain areas corresponding to their traditional clinical applications, partially validating the specificity of points described in traditional Chinese medicine.

Despite the encouraging results, the authors acknowledge important limitations and challenges. The main limitation is that current evidence is correlational, not establishing a direct causal relationship between DMN alterations and the therapeutic effects of acupuncture. The observed brain changes may be indirect consequences of other therapeutic mechanisms or even secondary byproducts of stimulation. In addition, the molecular and cellular mechanisms underlying brain networks such as the DMN are still poorly understood, making more precise interpretations difficult.

The complexity of acupuncture, with its multiple variables (type of stimulation, frequency, intensity, points used, individual response), makes it challenging to isolate specific mechanisms. The researchers propose a 'reverse translational' research strategy that combines studies in animal models using advanced techniques such as optogenetics and chemogenetics to establish causal relationships, which can subsequently inform and improve clinical studies in humans. This approach promises to definitively clarify whether and how DMN alterations causally contribute to the therapeutic effects of acupuncture, potentially revolutionizing our scientific understanding of this ancient practice and optimizing its modern clinical application.