Bertram, H. C. | bioRxiv Science

bioRxiv2026

Daily Bowel Movements are Associated with Stronger Gut-Brain Phase-Amplitude Coupling and Better Cognitive Performance

Gut-brain communication has emerged as a rapidly expanding field of research, with recent electrophysiological studies revealing rhythmic gut-brain coupling between gastric activity and brain oscillations in humans. Gut motility is a key determinant of gastrointestinal function, but it remains unclear whether individual differences in gut motility reflected by weekly bowel movements (e.g., defecation frequency) are associated with differences in gut-brain coupling. Here, we address this question by examining women with self-reported daily bowel movements (N = 38) and women with less frequent bowel movements (N = 38). We recorded simultaneous electroencephalography (EEG) and electrogastrography (EGG) at fasting state, performed cognitive assessments, and analysed faecal short-chain fatty acids (SCFAs) as markers of colonic fermentation. In a subset of participants, EEG-EGG coupling was assessed twice over an interval of at least eight weeks to assess test-retest reliability. In this group, EEG-EGG coupling showed moderate test-retest reliability (Intraclass Correlation Coefficient (ICC) = 0.50). When comparing the two groups of women, the phase-amplitude coupling (PAC) analysis between EEG and EGG signals revealed a significantly stronger gut-brain coupling in women with daily bowel movements compared to women with less frequent bowel movements (p = 0.03). We additionally found that women with daily bowel movements made less errors in the cognitive tasks and had higher levels of faecal SCFAs. A path analysis suggested that bowel movements significantly affect gut-brain phase-amplitude coupling through faecal SCFAs. However, neither faecal SCFAs nor phase-amplitude coupling significantly predicted cognitive performance, suggesting the existence of alternative pathways for the association between bowel movements and cognitive performance. Together, our findings suggest that the strength of gut-brain coupling is associated with bowel movements and cognitive performance, making EEG-EGG coupling a promising marker of human gut-brain interactions.

neuroscience↗

bioRxiv2023

The effect of colonic pH on microbial activity and metabolite production using common prebiotics as substrates: an in vitro study

The interplay between gut microbiota (GM) and host via degradation of dietary components leading to the production of metabolites such as short-chain fatty acids (SCFAs) is affected by a range of factors including colonic pH and carbohydrate source. Here we investigate how differences in colonic pH influence GM composition and metabolite production using different substrates including inulin, lactose, Galactooligosaccharides (GOS), and Fructooligosaccharide (FOS) in an in vitro colon setup. We investigated 3 different pH regimes (low, 5.2 increasing to 6.4; medium, 5.6 increasing to 6.8 and high, 6.0 increasing to 7.2) and found that Bacteroides spp. decreased but Bifidobacterium spp. became abundant under low pH regimes, suggesting complex interactions of the bacterial community in the face of pH fluctuations in the colon. The butyrate producers Butyricimonas and Christensenella were enriched at higher pH conditions, where also butyrate production was increased using inulin as substrate. The relative abundance of Phascolarctobacterium, Bacteroides, and Rikenellaceae was also increased at higher colonic pH, which was accompanied by increased production of propionate using GOS and FOS as substrate. The gastrointestinal factors are linked in a complex network, where microbial activity leads to the production of SCFAs and other compounds that influence pH, which in turn seems to influence microbial activity. Taken together, our results show that dynamic changes in colonic pH under in vitro simulated conditions have a strong effect on gut microbial activity with SCFA production being higher at colonic pH conditions close to neutral.

microbiology↗