Extroverts have more sensitive brain-reward system

Extroverts may be more outgoing and cheerful in part because of their brain chemistry, a new study has found.
Neuroscientists from Cornell University sheds new light on how differences in the way the brain responds to reward translate into extraverted behaviour.
People's brains respond differently to rewards, said neuroscientists. Some people's brains release more of the neurotransmitter dopamine, which ultimately gives them more reasons to be excited and engaged with the world, said Richard Depue, professor of human development in the College of Human Ecology, and co-author of the study.
"Rewards like food, sex and social interactions as well as more abstract goals such as money or getting a degree trigger the release of dopamine in the brain, producing positive emotions and feelings of desire that motivate us to work toward obtaining those goals," Depue said.

"In extroverts, this dopamine response to rewards is more robust so they experience more frequent activation of strong positive emotions," he said.
"Dopamine also facilitates memory for circumstances that are associated with the reward. Our findings suggest this plays a significant role in sustaining extroverted behaviour.

"The extroverts in our study showed greater association of context with reward than introverts, which means that over time, extroverts will acquire a more extensive network of reward-context memories that activate their brain's reward system," he said.
Researchers engaged 70 young adult males - a mix of introverts and extroverts according to a standard personality test - in a set of laboratory tasks that included viewing brief video clips of several aspects of the lab environment.

On the first four days, some participants received a low dose of the stimulant methylphenidate (MP), also known as Ritalin, which triggers the release of dopamine in the brain; the others received either a placebo or MP in a different lab location.
The team tested how strongly participants associated contextual cues in the lab (presented in video clips) with reward (the dopamine rush induced by MP) by assessing changes in their working memory, motor speed at a finger-tapping task and positive emotions (all known to be influenced by dopamine).
Participants who had unconsciously associated contextual cues in the lab with the reward were expected to have greater dopamine release/reward system activation on day 4 compared with day 1 when shown the same video clips.

This so-called "associative conditioning" response is exactly what the team found in the extroverts. The extroverts strongly associated the lab context with reward feelings, whereas the introverts showed little to no evidence of associative conditioning.
The study was published in journal Frontiers in Human Neuroscience.