University of Minnesota researchers studied the personalities of young adults ages 18 to 40 who underwent MRI brain scans to assess the sizes of different regions of their brains.

Extroverts had significantly larger volume in the medial orbitofrontal cortex, an area behind and above the eyes.

This region controls the brain’s reward system, which may reflect an extrovert’s pursuit of excitement and adventure.

Conscientious volunteers had larger volume in the lateral prefrontal cortex, which controls a person’s ability to plan ahead.

In subjects who scored low on emotional stability (i.e., high on neuroticism), brain volume was larger in the dorsomedial prefrontal cortex, and in the medial temporal lobe, an area under the temples that controls emotional reactions.