The growth of cognitive impairment (CI) in clinical practice makes us search for their new pathogenetic mechanisms, among which the effect of intestinal microbiota on the brain is currently being actively studied. The mechanisms of interaction of the axis “brain - microbiota” have not been completely studied. The aim of this study was to confirm the possible effect on the brain of the neurotoxin ammonia, which rises in the blood due to the syndrome of excessive bacterial growth (SIBO). Materials and methods: The article presents data from a clinical observation, which included an examination of 70 patients of the gastrocenter in Perm with dyspepsia syndrome, who studied changes in the intestinal microbiota, the level of ammonia of capillary blood, and cognitive impairment, and conducted a correlation analysis. Results: According to the results of a statistical analysis of the obtained data, we did not find any significant changes or significant correlations between the studied parameters. However, the identified tendency in the connection “SIBO - hyperammonemia - cognitive impairment” suggests that the presence of SIBO can aggravate the severity of not only existing gastroenterological manifestations, but also be a risk factor for hyperammonemia, as well as contribute to the formation of impaired human cognitive functions.