Research on gut–brain communication has expanded recently, including electrophysiological evidence of rhythmic coupling between gastric activity and brain oscillations in humans. Gut motility and bowel movement frequency are core aspects of gastrointestinal function, but whether individual differences in motility relate to measurable differences in gut–brain coupling had been unclear. This study examined whether self-reported weekly bowel movement frequency associates with measures of gastric–brain interaction and cognitive performance in healthy women.
The analysis compared two groups of women: those reporting daily bowel movements (N = 38) and those reporting less frequent bowel movements (N = 38). Primary measures included simultaneous electroencephalography (EEG) and electrogastrography (EGG) recorded in the fasting state, cognitive task performance summarized as a global cognitive composite error score, and faecal short-chain fatty acids (SCFAs) quantified as markers of colonic fermentation.
Simultaneous EEG and EGG recordings were used to probe EEG–EGG coupling. The authors applied a phase–amplitude coupling (PAC) analysis to evaluate how the phase of gastric rhythms related to the amplitude of brain oscillations. PAC served as a principal electrophysiological index of rhythmic gut–brain interaction in the study.
A subset of participants underwent repeated EEG–EGG assessment at least eight weeks apart to evaluate stability of the coupling measure. In this subgroup, the EEG–EGG coupling exhibited moderate test–retest reliability, with an intraclass correlation coefficient reported as ICC = 0.50, indicating that PAC measurements showed reproducible signal components across sessions but also notable variability.
Comparing the two bowel-frequency groups, the PAC analysis revealed a significantly stronger gut–brain phase–amplitude coupling in women with daily bowel movements than in women with less frequent bowel movements (p = 0.03). This result supports an association between habitual defecation frequency and the strength of electrophysiological gut–brain interactions measured by EEG–EGG PAC.
Behaviorally, women reporting daily bowel movements committed fewer errors on the cognitive tasks, reflected by a lower global cognitive composite error score. While bowel movement frequency was negatively associated with the error score (meaning more frequent bowel movements coincided with better cognitive accuracy), the study reported that neither faecal SCFAs nor PAC significantly predicted cognitive performance in the multivariate models presented.
Faecal SCFAs, assayed as markers of colonic fermentation, were higher in the daily bowel movement group. The investigators included SCFAs in path analysis to explore whether colonic fermentation markers could mediate relationships between bowel habits and gut–brain coupling.
A path analysis reported that bowel movement frequency significantly affected gut–brain PAC through faecal SCFAs, suggesting a possible mediation pathway from motility to electrophysiological coupling via colonic fermentation metabolites. However, the same models found that neither faecal SCFAs nor PAC significantly predicted cognitive performance, indicating that the observed association between bowel movement frequency and cognition may operate through additional or alternative mechanisms not captured by SCFAs or PAC in this dataset.
These findings indicate that habitual bowel movement frequency is associated with measurable differences in EEG–EGG coupling and with cognitive performance in this sample of women. The moderate test–retest reliability (ICC = 0.50) suggests PAC from simultaneous EEG and EGG has potential as a biomarker of human gut–brain interaction but also that individual measurements may vary over time.
The reported path analysis supports a role for faecal short-chain fatty acids in linking bowel habits to gut–brain electrophysiology, but the absence of direct prediction from SCFAs or PAC to cognitive outcomes points to unmeasured pathways or additional factors underlying the bowel habit–cognition relationship. The study sample, group definitions based on self-reported bowel frequency, and the observational design constrain causal inference.
Overall, the authors propose EEG–EGG coupling as a promising marker for human gut–brain interactions and highlight relations among bowel movements, colonic fermentation markers, electrophysiological coupling, and cognitive performance. Specific numerical outcomes reported in the source include a significant group difference in PAC (p = 0.03) and a test–retest ICC of 0.50. Further work is required to clarify causal pathways and to assess generalizability across populations.