Introverts and extraverts alike have a reward system in the brain that has the same purpose and that functions the same way. However, all brains don’t process rewards identically. Whether intrinsic or extrinsic, rewards are an important element of behavior change, which is why I became interested in the subject after noticing that some of my clients have a harder time than others in getting the hang of using rewards.

It’s commonly believed that the primary difference between extraverts and introverts is each group’s desire for alone time. Introverts want and need more of it, and extraverts want and need less of it. Although that’s not necessarily inaccurate, it’s wrong to assume that extraverts always prefer social interaction over alone time. And even if they do, that isn’t what differentiates one group from the other.

Research suggests that what distinguishes extraverts from introverts is sensitivity to rewards in the environment. A preference for social interaction—independent of the reward/enjoyment of the interaction—is not what’s at the core of extraversion. According to Colin G. DeYoung, Ph.D. (researcher in the field of personality neuroscience):

People who score low in Extraversion are not necessarily turned inward; rather, they are less engaged, motivated, and energized by the possibilities for reward that surround them. Hence, they talk less, are less driven, and experience less enthusiasm. They may also find levels of stimulation that are rewarding and energizing for someone high in Extraversion merely annoying or tiring (or even overwhelming). Their reserved demeanor is not likely to indicate an intense engagement with the world of imagination and ideas, however, unless they are also high in Intellect/Imagination.

It’s All in Your Head

Extraversion/introversion isn’t merely a psychological concept. The differences can be observed in the brain. According to DeYoung, the unifying function of dopamine is exploration. The release of dopamine increases motivation to explore and facilitates cognitive and behavioral processes useful in exploration. When dopamine floods the brain, both introverts and extroverts become more talkative, alert to their surroundings, and motivated to take risks and explore the environment. Both introverts and extroverts have the same amount of dopamine available, but dopamine is more active in the brains of extroverts than in the brains of introverts.

Here are some of the other differences that have been observed in the brains of extraverts and introverts.

GENES

Although no one gene determines temperament, D4DR (“the novelty seeking” gene) is found on the 11th chromosome which has been deemed the personality chromosome because of its influence on behavior, particularly exhilaration and excitement. Thrill seekers examined in a study conducted by geneticist Dr. Dean Hamer were shown to have a long D4DR gene and were less sensitive to the neurotransmitter dopamine. Those participants with more reflective and slower paced natures had shorter D4DR genes and a higher sensitivity to dopamine.

BLOOD FLOW

Rev up: In extraverts’ brains, blood flows in shorter pathways toward parts of the brain where external stimuli (visual, auditory, touch, and taste—but not smell) are processed. The neuropathways most used by extraverts are activated by dopamine. Extraverts, who tend to have a novelty seeking personality and can process a higher amount of external stimuli, are less sensitive to dopamine. Their brains use adrenaline to make more dopamine.

As a result, the brain becomes alert and hyper-focused on its surroundings. Blood sugar and free fatty acids are elevated to provide more energy, and digestion is slowed. Thinking is reduced, and the person becomes prepared to make snap decisions. While extraverts thrive on the dopamine-charged good feelings created when they engage the sympathetic nervous system, for introverts, it’s too much.

Throttle down: Introverts have more blood flow to their brains than extraverts, and the blood in introverts’ brains travels longer, more complicated pathways and focuses on parts of the brain involved with internal experiences such as remembering, solving problems, and planning. The more dominant neurotransmitter in introverts’ neuropathways is acetylcholine, which affects attention and learning, influences the ability to stay calm and alert, utilizes long-term memory, and activates voluntary movement. Acetylcholine makes us feel good when we think and feel.

GRAY MATTER

A 2012 Harvard University study revealed that introverts tended to have larger, thicker gray matter in their prefrontal cortex—a region of the brain that is linked to abstract thought and decision-making—while extraverts had less gray matter. The study’s author concluded this might account for introverts’ tendencies to sit in a corner and ponder things thoroughly before making a decision, and extraverts’ ability to live in the moment and take risks without fully thinking everything through (which has its cons and benefits, of course).

FACIAL RECOGNITION

The brains of extraverts pay more attention to human faces than do introverts. Introverts’ brains don’t seem to distinguish between inanimate objects and human faces.

Experiencing Rewards

Extraverts tend to experience more positive feelings and get more out of rewards in general, and they are more likely to seek and spend more time on rewarding activities. When they do, they also experience a higher boost in momentary happiness as compared to their introverted counterparts. This partly explains the direct relationship between extraversion and momentary happiness. [The relationship between extraversion and happiness or subjective well-being (SWB) is one of the most consistently replicated and robust findings in the SWB literature. –W. Pavot, E Diener, F. Fujita]

Extraverts are more likely to go for immediate gratification, while introverts tend to delay rewards and instead invest in the hope of a larger payoff down the road. They are significantly more likely to prefer smaller, immediate rewards compared with introverts overall. When extraverts are in a good mood, they are even more likely to choose an immediate reward. Regardless of mood, introverts were more likely than extraverts to prefer delayed rewards.

Extraverts are already sensitive to rewards, so when they are in a positive mood it primes the brain’s reward system even more, so they’re focused on immediate opportunities. That may explain why extraverts are so impulsive, since when they are exposed to potential rewards that puts them into a positive mood, which in turn cues them that now is the time to pursue that reward.

The reason extraverts seem to experience stronger positive emotions may be based on how their brains process the memory of rewards. Dopamine affects how we feel when we recall a reward. Stronger dopamine response in relation to the memory of a first kiss, for example, carries with it a certain rush (associative conditioning).

The brains of extraverts show an extremely high level of associative conditioning, while the brains of introverts showed essentially none. Over time, the brains of extraverts “collect” an increasingly more robust network of reward-memories. Recalling these memories triggers their brains’ reward system, eliciting positive emotions.

Introverts brains don’t do this sort of reward collecting—or at least they don’t do it nearly as much or as strongly as the brains of extraverts. On a day-to-day basis, introverts have less of a reward-memory network to rely on for a “boost,” while their extraverted counterparts are able to tap into their networks for boosts aplenty.

Extraverts report more happiness than introverts during effortful “rewarding” activities, such as sports and exercise, and financially rewarding work tasks. No difference was found in extraverts’ and introverts’ happiness during low-effort, low importance “pleasurable, hedonic” activities, such as watching TV, listening to music, relaxing, and shopping. Given that extraverts experience more happiness during rewarding activities, but not during pleasurable activities, it may be that extraverts don’t have a more responsive pleasure system, but rather a more active and responsive “desire system.”

Extraverts experience a bigger happiness boost than introverts when they perform rewarding activities with other people, rather than alone. Extraverts spend more time on rewarding activities than introverts, and they tend to have more social contact during their daily activities.

The brain’s reward system generally operates outside our conscious awareness, so it can be difficult to identify rewards. Some people are more resistant to rewards than others. As far as the brain is concerned, anything that produces a hit of dopamine is good regardless of our opinion of it. If you want to get serious about long-term behavior change, it’s important to understand the role of rewards and the way your particular brain responds to them.