He said that the serotonin system, which helps regulate mood, does not develop properly if there is not enough bacteria in the gut. Mice in the study who did not have enough bacteria were less interested in new social situations than mice with a normal level of bacteria.
The scientists said that the bacteria deficient mice behavior resembles social cognition deficits of patients. Children with autism also show repetitive behaviors and scientists pointed out that gut problems are common among those with autism. Scientists weaned bacteria and then added it and this reversed the mice’s social avoidance and repetitive behaviors, but had no impact on social cognition impairments.