Extraversion is a Big Five trait that explains individual’s ability and tendency to explore, interact, and engage with external rewards. This tendency commonly manifests itself in outgoing, social behavior and it’s usually easy to observe.
Extraversion has two known sub-traits (DeYoung, 2016):
Both Assertiveness and Enthusiasm have been linked to a number of underlying neurobiological causes, some more substantiated than others.
Dopamine is a chemical that powers your brain’s reward system. When you want a specific reward, your dopamine system is driving the experience.
There is significant evidence that people with highly active dopamine systems are more sensitive to external rewards. Their brain truly makes them want something more than others, which can drive assertive behavior.
However, the increased wanting for a reward has not been found to translate into increased liking or pleasure derived from the reward - only the pursuit.
This relationship between Assertiveness and the dopamine system has been well-validated in pharmacological studies, behavior experiments, EEG studies, and neuroimaging research.
Enthusiasm, the component of Extraversion characterized by sociability, gregariousness, and positive emotionality, can be linked to the experience of liking a reward.
The drive towards a reward (driven by dopamine) is not necessarily enjoyable in itself (we often say that we’re “dying” to get something), but we know that acquiring a reward can be very enjoyable (both in humans and animals).
While researchers have not found a strong association between dopamine levels and these positive feelings, multiple studies suggest that the opiate system may have a strong influence. This hypothesis is not as well-supported as the link between dopamine and Assertiveness, but there some compelling findings that make it very plausible.
If this is true, it means that people who have a higher level of Enthusiasm may have a chemical makeup that causes them to feel more pleasure from rewards than most other people.
Next, we'll go over the neurobiological causes of Agreeableness.