The current diagnosis of anxiety, depression and other psychiatric disorders is mainly based on scale scores. However, scale assessment is highly subjective, and some subjects have limited literacy and are unable to accurately understand the content of the scales. In addition, most of the scales applied originate from the West, and when translated, they may not be able to effectively convey the meaning of the original scales due to textual differences, resulting in lower scale reliability and validity [13]. These factors will greatly affect the effectiveness of scale measurement and disease diagnosis and treatment, thus increasing patient mortality and socio-economic burden. In this study, we selected a multichannel EGEG to objectively record the gastrointestinal myoelectrical activity of a natural population with no gastrointestinal discomfort within 6 months and no history of drug use within 1 week, and found that the mean amplitude and response area of the gastrointestinal electrical signals, especially in the intestinal channel, could effectively reflect anxiety and depression disorders.

EGEG, similar to electrocardiograph (ECG) and electroencephalogram (EGG), is a method of recording gastrointestinal myoelectrical activity on the surface of abdominal surface using skin electrodes, which is convenient, non-invasive and objective [14]. Because the gastrointestinal electrical signal is considerately weak and slow, the amplitude of which is only 1/1000 of that of ECG, the research on EGEG has started rather late and developed slowly [15]. EGEG have now been used as a routine clinical aid in diagnosis. A large number of studies have shown that EGEG has good diagnostic role in gastrointestinal diseases such as gastritis, gastric ulcer, tachycardia/bradycardia, etc. It also has some diagnostic significance for functional dyspepsia with obesity, motion sickness, post-surgical gastrointestinal dysfunction [16,17,18]. Although worldwide researchers have figured out certain rules for the clinical research of electrogastrogram, some criteria have been developed for the auxiliary diagnosis of diseases, such as low amplitude (< 150µV) for gastritis, high amplitude (> 250µV) and high frequency (> 3.5CPM) for gastric ulcer. However, there is still a lack of unified expert consensus on the study of intestinal electrograms, and researchers are still trying to explore and summarize them in depth [19, 20]. This study for the first time found that the diagnostic significance of intestinal electrograms for mental illness is higher than that of gastric electrograms, which will also further contribute to the development of intestinal electrograms and promote the formation of a standardized interpretation scheme and a more scientific and effective delineation of critical values.

Moreover, considering the potential variation in the anatomical positioning of the stomach and intestines among subjects, we addressed this concern by employing a multichannel gastrointestinal electrography instrument. This instrument enabled the collection of gastrointestinal myoelectrical activity from four distinct sites in both the stomach and intestines. Subsequently, through correlation analysis, we observed a substantial correlation between channels one to four in the stomach and channels five to eight in the intestines. Consequently, we opted for channel integration as a method to substitute the gastrointestinal myoelectrical activity, utilizing the combined parameters from both gastric and intestinal channels. This approach served to mitigate potential result biases stemming from inter-individual organ positioning discrepancies.

Although EGEG have been reported to be associated with depression and anxiety in previous studies, most of them have been applied to patients with gastrointestinal disorders, such as observing the improvement effect on depression and anxiety by relieving gastrointestinal discomfort. It has not been directly investigated whether EGEG can be used as an objective diagnostic tool for mental disease. Therefore, the present study provides strong evidence that abnormality gastrointestinal myoelectrical activity is observed among participants of anxiety and depression without gastrointestinal dysfunction, as evidenced by a decrease in the mean amplitude and response area.

According to epidemiological data, the prevalence of depression is about 1.5-3 times higher in women than in men [21, 22], and the gender distribution of the subjects in this study showed that women are about 3 times more likely to be depressed than men, which is consistent with the disease characteristics. In addition, in the traditional diagnosis of depression and anxiety, the depression self-rating scale, anxiety self-rating scale, and Hamilton anxiety scale are often selected, but these scales have more questions and complicated items, which are not conducive to use in natural population cohorts [23]; in contrast, the PHQ-9 and GAD-7 selected in this study have fewer questions, condensed items, and high reliability, which are more effective in cohort screening. After we found depression and anxiety judged on the basis of total scale scores were correlated with EGEG, the core items of the scale that reflect the core symptoms of depression and anxiety were also correlated with gastrointestinal electrical parameters (r > 0, p < 0.05), further suggesting that EGEG can objectively reflect anxiety-depression disorder.

On this basis, we further classified the population according to different genders (male/female) and different ages (over 60 years old for elderly and 18–60 years old for young adults). We found that females were similar to males, and there were no significant differences in all channel parameters between those with ADD and healthy participants. The MA and RA of those with ADD were significantly lower in the elderly than in the healthy control population (p < 0.05), while in young adult subjects, there was no significant difference between the two groups compared to each parameter. This shows that EGEG can not only reflect anxiety-depression disorders, but also have a significantly higher diagnostic value in the elderly than in young adults.

Nevertheless, the study included several limitations. Although the results came from multi-centers of Western China, the sample size was still relatively small. Expanded size and incorporated participants in other areas are essential in the future. Furthermore, this was a cross-sectional study and only measured gastrointestinal myoelectrical activity once, the causality could not be drawn. In future studies, the gastrointestinal electrical activity and mental state of the participants at multiple time points can be measured through follow-up, which is helpful to establish the dynamic relationship between gastrointestinal electrical activity and anxiety-depression disorder.