Gut and Oral Microbes May Be Linked to Psychopathic Traits

The more scientists learn about the microbiome, the clearer it becomes that it has a remarkably deep influence on the people we become.

Microbes living in the body are already known to affect our emotions, including how we respond to fear. But just how extensively might they shape personality?

Research indicates that the answer may be: quite extensively.

An early-release study published in Translational Psychiatry has uncovered evidence that microbiota could even affect how people experience psychopathy. The researchers identified links between the abundance of particular gut and oral microbes and psychopathic personality traits.

The findings have not yet been peer reviewed. Nevertheless, the team says this is the first evidence indicating how microbiota might contribute to psychopathic traits, whose biological foundations remain poorly understood.

Psychopathy and the microbiota connection

Psychopathy is a personality construct associated with traits such as reduced empathy, antisocial tendencies, impulsiveness and egoism. However, the origins of psychopathic personalities are still not fully understood.

Video: YouTube

People with psychopathy can share similarities in brain structure. Particular brain regions and pathways, including the prefrontal cortex, have often been connected to the phenomenon.

Yet, the researchers argue that this cannot be the whole explanation.

"Though brain alterations, particularly in the prefrontal cortex and temporo-limbic areas, are suggested to be directly implicated in psychopathy, these alone are insufficient to provide a comprehensive neurobiological explanation for psychopathic behavior," researchers explain in their paper, led by first author and biomedical scientist Carolina Costa of the University of Porto in Portugal.

"We hypothesized that the composition of the gut and oral microbiota may be associated with subclinical psychopathic personality traits… To our knowledge, this is the first study to explore this association."

How the gut and oral microbiota were studied

Costa and colleagues examined 200 healthy adult participants. Each completed the Self-Report Psychopathy Scale-Short Form, a questionnaire developed to assess psychopathic traits, and provided blood, saliva and faecal samples. These were tested for the body's bacterial composition and for a range of metabolic markers.

Psychopathy is a personality construct marked by lack of empathy, antisocial tendencies, impulsiveness, and egoism. (disqis/Getty Images)

Analysing the diversity of each person's gut and oral microbes individually revealed no distinct connection with psychopathy. However, a different pattern emerged when researchers compared participants' results with one another.

Viewed this way, greater abundance of three particular bacterial types was positively associated with more pronounced psychopathic traits.

According to this analysis, having more microbes from the genera Allisonella or Prevotella in the gut microbiome, or more of the species Cloacibacillus evryensis, may make a person more likely to display psychopathic traits.

It is important to note that these results cannot establish causation: the study identifies correlations in the data only.

Bacteria associated with psychopathic traits

If these microbes did hypothetically influence behaviour towards psychopathic tendencies, how could that happen?

The answer is uncertain. However, the researchers note that Allisonella has previously been associated with several human diseases. Its possible capacity to promote inflammation - which is linked to anxiety and depression - may help account for its potential involvement in psychopathy.

Likewise, Prevotella has previously been connected to neuropsychiatric disorders and is thought to influence emotional processing. The association involving C. evryensis, meanwhile, could stem from its suspected role in producing gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter involved in systems governing impulse control.

One species produced the opposite association. Higher amounts of Treponema vincentii in the oral microbiome were associated with fewer markers of psychopathy, though the researchers acknowledge that they cannot explain why.

Related: Scientists Developed a Questionnaire to Identify if Your Cat Is a Psychopath

Considerably more investigation will be needed to clarify how gut microbes might contribute to psychopathic traits. Still, the results offer important new avenues for research and could eventually assist clinicians in identifying people who exhibit these dark impulses.

"Overall, our findings highlight the potential of microbiota and their metabolic outputs as biomarkers for psychopathic traits in the general population," the researchers write.

"The associations we observed, particularly between specific taxa (e.g., Allisonella, Prevotella, C. evryensis, T. vincentii) and traits such as callousness, manipulation, impulsivity, and anti-sociality, suggest a measurable biological footprint for psychopathy that extends beyond traditional neurocognitive models."

The findings are reported in Translational Psychiatry.

This article was fact-checked and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please let us know.