Effects of acupuncture on the brain in primary insomnia: a coordinate-based meta-analysis of fMRI studies

Primary insomnia is a health problem affecting millions of people worldwide, characterized mainly by difficulties initiating and maintaining sleep, reaching 6 to 10% of the global population. This condition not only impairs daytime performance but also significantly increases the risk of developing psychiatric disorders such as depression and anxiety. Conventional treatment of insomnia generally involves medications and cognitive behavioral therapy; however, medications can cause serious adverse effects, including dependence, cognitive deficits, mental confusion, and falls. For this reason, researchers have explored other effective therapeutic options with fewer adverse effects.

Acupuncture, a millennia-old technique of traditional Chinese medicine that involves the insertion of fine needles at specific points on the body, has emerged as a promising alternative for the treatment of primary insomnia, recognized by many physicians and patients because of its few adverse effects. Several studies have suggested that acupuncture can improve objective sleep parameters and induce changes in specific brain regions.

This study aimed to perform a systematic review and coordinate-based meta-analysis to summarize the scientific literature on functional magnetic resonance imaging assessment of patients with primary insomnia treated with acupuncture. The investigators conducted a methodologic and comprehensive search in multiple scientific databases from inception through December 2022, including Web of Science, PubMed, ScienceDirect, Embase, and Chinese databases such as Wan Fang, China National Knowledge Infrastructure, and Chinese Scientific Journal Database. Study quality was assessed by three independent investigators using standardized tools. To investigate the central mechanisms of acupuncture treatment in primary insomnia, a sophisticated technique called SDM-PSI meta-analysis (Seed-based D-mapping meta-analysis with permutation of subject images) was applied, which allows for integrated and reliable analysis of neuroimaging data.

The analysis included a total of 305 patients with primary insomnia and 116 healthy controls from 11 scientific studies. The results of the SDM-PSI analysis revealed important findings about how primary insomnia affects the brain and how acupuncture can modify these alterations. Patients with primary insomnia showed increased brain activity in specific regions compared with healthy people, particularly in the left superior frontal gyrus, right angular gyrus, and cerebellum. After acupuncture treatment, significant improvements were observed in the function of several brain regions, including the right superior frontal gyrus, left inferior frontal gyrus, left inferior temporal gyrus, left supramarginal gyrus, bilateral precuneus, left supplementary motor area, and right parahippocampal gyrus.

Interestingly, when acupuncture was tested at sham points (non-acupoints), the effects were concentrated mainly in the frontal lobe, suggesting that the specific location of the needles is important to obtain broader benefits. The included studies presented some methodological limitations, including high performance bias and attrition bias as assessed by the quality tools.

The clinical implications of these findings are significant for both patients and health care professionals. The results demonstrate that acupuncture produces measurable and specific neurological effects in patients with primary insomnia, mainly affecting the brain's default mode network, which is involved in cognitive and self-awareness processes. The frontal lobe, responsible for functions such as problem solving, working memory, planning, and evaluation of goal-directed activities, proved to be a key area in both insomnia pathology and the therapeutic mechanism of acupuncture. Strengthening of frontal function may help relieve subjective insomnia and the environmental discomfort experienced by people with primary insomnia, thereby reducing pre-sleep worry and rumination.

The precuneus, a region fundamental for memory of past events and self-esteem, was also significantly affected by acupuncture, suggesting that the treatment can improve self-perception and perception of the environment, reducing the occurrence of negative sleep-related memories. These findings provide a solid scientific basis for understanding how acupuncture works in the brain of patients with insomnia, validating its clinical use through objective neurobiological evidence.

This study has some important limitations that should be considered when interpreting the results. First, only 11 studies were included in the analysis, which represents a relatively small number for a robust meta-analysis. In addition, the studies presented major differences in clinical protocol design, choice of acupuncture points, and analytic methods, which may have affected the reliability of the results. Most studies did not adequately describe blinding methods and concealment of group allocation, resulting in some degree of methodological bias.

Another limiting factor was that only publications in Chinese and English were included, which may have excluded relevant studies in other languages. The investigators also did not test for between-study heterogeneity, an important consideration in meta-analyses. Despite these limitations, this is the first systematic review to use coordinate-based meta-analysis to examine the effects of acupuncture on the brain of patients with primary insomnia, providing valuable evidence on acupuncture-induced neuroplasticity. For future research, studies with larger samples and more rigorous randomized clinical trials are needed to improve the reproducibility and accuracy of results, in addition to standardizing sham acupuncture control groups and applying more uniform implementation standards for equipment selection, patient characteristics, and outcome assessment.