As people age, brain size declines. However, higher levels of conscientiousness are associated with a larger brain volume with advancing age.

What this means is that people who are more conscientious may actually be altering their brain structure.

Researchers at the University of Minnesota studied more than 100 volunteers ages 18 to 40 and determined their personality traits using standardized assessment instruments.

They also analyzed the results of magnetic resonance imaging (MRI) brain scans to measure the volumes of specific brain areas.

In the journal Psychological Science, they reported that the size of the lateral prefrontal cortex was significantly larger in volunteers who scored high in conscientiousness.

That part of the brain is involved in complex problem-solving and decision-making, both of which are mental skills that become fine-tuned in conscientious people.

Investigators at the Massachusetts Institute of Technology performed functional MRI studies to determine how personality traits influence brain function.

They asked volunteers to plan a task in which they would either receive a smaller monetary reward sooner or a larger one later.

Overall, higher conscientiousness was associated with a greater preference for delayed rewards.

But brain regions controlling thinking and rewards showed greater activity when volunteers selected a smaller reward that they would receive sooner.