Chimpanzees' personality traits are linked to the anatomy of specific brain structures, according to researchers. The researchers studied 107 chimpanzees' brains using magnetic resonance image (MRI) scans and also assessed each chimpanzee's personality by using a 41-item personality questionnaire. They found chimpanzees who were rated as higher for the personality traits of openness and extraversion had greater gray-matter volumes in the anterior cingulate cortex in both hemispheres of the brain.