Microbiota-Gut-Brain Axis: Behaviour and Dementia Implications

A diverse gut microbiome has been associated with behaviours related to positive mood, curiosity, sociability, and impulsivity according to researchers studying toddler behaviour and their microbiome. Extroverted behaviour in boys was associated with bacteria of the Parabacteroides, Rikenellaceae, Ruminococcaceae families and Dialister genera, while girls with an abundance of Rikenellaceae displayed more fear behaviours than girls with a diverse microbiome. A less diverse microbiome was associated with behaviours such as self-restraint, cuddliness, and focused attention in girls. The researchers noted that a child’s temperament, or how they handle stress, was influenced by their gut microbiome, especially for boys.

There is a link between anti-social behaviours and a gastrointestinal environment enriched with Clostridiales spp in an animal model. Behaviours associated with depression, such as social avoidance and despair-like behaviours, were prevented by the administration of a broad-spectrum antibiotic cocktail. The behaviours of social avoidance and despair were transferred to germ free mice, after a fecal transplant consisting of Clostridiales, Lachnospiraceae and Ruminococcaceae spp. Researchers also noted a disruption in gut biosynthesis of tryptophan, tyrosine, and phenylanine in recipient mice with behavioural changes. The underlying mechanism of action linking the microbiota-gut-brain axis and behaviour may lie in key bacterial metabolites effecting gene expression in the prefrontal cortex and gut derived amino acids.

New research linking childhood behaviour to the development of dementia later in life suggests the microbiota-gut-brain axis might influence cognition decades before symptoms appear. Researchers found that vigor, calm, and maturity behaviours in adolescence were associated with lower risk of dementia 54 years later. We now know that behaviour is influenced by the microbiota, and it has been established that the development of dementia is linked to the microbiota. Although we do not have data in this study on the adolescents’ microbiota in relation to the development of dementia, future studies should include microbiome profiling and metabolism due to a potential link. Future studies to identify bacterial metabolites of the microbiota-gut-brain axis could direct novel preventative treatment options for neurocognitive disorders. Psychobiotics, bacteria administered for mental health benefit, may be utilized prophylactically and as potential adjunctive treatment.

While the microbiota-gut-brain axis has been implicated in neurological conditions, it is also at play influencing quotidian behavior. The proposed mechanism of action lies in bacterial metabolites which influence the pre-frontal cortex and gut derived amino acids. Adolescent behaviour has proven predictive of dementia development decades later, therefore a potential link exists between the adolescent microbiota and dementia pathogenesis. In light of this new evidence, further research into microbiome profiling and metabolism in relation to neurocognitive disorders is warranted. Clinicians can rest assured addressing the microbiota will benefit their patients, not only in the immediate future, but potentially decades down the line as well.