Neuroimaging studies in healthy individuals and those with brain diseases have revealed a relationship between personality traits and specific brain regions. Generally, the right hemisphere of the brain plays a more central role than the left in social and emotional behavior, thus many regions related to personality are primarily right-sided. Some of the main research findings involve traits related to the Big Five factors Extraversion and Agreeableness:

• Extraversion — Extraverted people tend to seek out social interactions and engage in them in an active, often highly verbal manner. Accordingly, extraversion mostly relates to dorsolateral frontal lobe regions associated with action planning, task management and goal setting. In addition, extraversion correlates with brain regions involved in emotion processing such as the insula and the anterior cingulate, reflecting the emotional aspects of social engagement.
• Warmth — Warm-hearted people also seek social interactions, but desire to provide care and support to others, even to the extent of often putting others’ needs above their own. In line with this behavioral pattern, the personality trait warmth relates extensively to brain regions involved in emotion processing, including the amygdala, temporal pole, insula, anterior cingulate, and the most anterior parts of the frontal lobes.
• Dominance/Assertiveness — Dominance reflects the tendency to negotiate with one’s environment to accomplish personal goals, regardless of whether those goals conflict with those of others. Thus, similarly to extraversion, dominance relates to brain regions involved in action planning and task management; however, in contrast to extraversion, dominance does not appear to involve brain regions that mediate emotion processing.

Though there is now considerable evidence for a structural basis for personality in the brain, other non-structural organic and environmental factors influence personality as well. For instance, depressed individuals likely have altered neurotransmitter and hormone levels in the brain, and might become less extraverted, warm-hearted and assertive even without structural brain changes. Individuals with language problems severe enough to impair their communication with other people might become less extraverted and assertive because they can no longer accomplish their interpersonal goals verbally.