Acupuncture-induced changes in functional connectivity of the primary somatosensory cortex varied with pathological stages of Bell's palsy

Bell's palsy is the most common cause of facial nerve paralysis, affecting thousands of people each year. In traditional Chinese medicine, acupuncture is widely used to treat this condition, but the mechanisms by which it exerts its therapeutic effects were not yet fully understood. This pioneering study used functional magnetic resonance imaging (fMRI) to investigate how acupuncture alters brain connectivity at different stages of Bell's palsy. The researchers recruited 28 patients with unilateral Bell's palsy and 20 healthy controls.

Patients were stratified into three groups based on disease duration and degree of recovery: an early group (less than 14 days of symptoms), a late group (more than 14 days), and a recovered group (normal facial function). All participants underwent an acupuncture session at LI-4 (Hegu, 合谷), located on the dorsum of the hand, while undergoing functional MRI. The selection of this point is based on the Chinese medicine theory that the cortical representations of the hand and face are adjacent in the brain. The results revealed a striking pattern: acupuncture induced significant changes in primary somatosensory cortex connectivity only in the actively recovering patient groups (early and late), but not in healthy controls or in the already recovered group.

More interestingly, the direction of these changes varied with pathological stage. In the early group, a significant decrease in connectivity was observed between the somatosensory cortex and several regions, including the primary motor cortex, superior parietal areas, supramarginal gyri, and middle temporal regions. This decrease may reflect the brain reorganization required to cope with the sudden loss of facial motor feedback. By contrast, in the late group, acupuncture induced an increase in connectivity between the somatosensory cortex and regions such as the inferior frontal gyrus, angular gyrus, precuneus, and posterior cingulate cortex.

This increase suggests that, at later stages, the brain develops more elaborate compensatory strategies, enhancing processing between somatosensory and motor regions. The fact that there were no significant changes in healthy controls or in the recovered group indicates that the efficacy of acupuncture may depend on the functional state of the brain at the time of treatment. In healthy individuals, where neural circuits are intact, acupuncture produces no measurable changes in connectivity. Similarly, in already recovered patients, where brain reorganization has been completed, the effects of acupuncture are minimal.

The clinical implications are significant. The findings suggest that acupuncture may facilitate adaptive neuroplasticity during different phases of recovery from Bell's palsy. In the early stage, it may help "disconnect" dysfunctional circuits, allowing reorganization. In the late stage, it may enhance the formation of new compensatory circuits.

The study also identified changes in regions associated with the brain's default mode network, including the precuneus and posterior cingulate cortex. These areas are involved in homeostatic regulation and the processing of internal experiences, suggesting that acupuncture may influence not only motor aspects but also bodily perception and the overall well-being of patients. Although promising, the results should be interpreted with caution because of several methodological limitations, including the absence of a sham acupuncture control group and the relatively small sample size.