Why is it that some people enjoy going to parties, doing conferences, talking in public, and others absolutely do not? Well, according to a widely acknowledged Five-Factor Model of Personality, it seems that there are rather fundamental differences between the two types of personality traits introversion and extraversion.
In the Five-Factor Model, the trait extraversion is one of the big five personality factors. Extraversion and introversion represent a continuum between extreme extraversion and extreme introversion. People usually lie somewhere in between the two extremes.
So, why do some people like their own company more than their friends’? In fact, there is a very interesting theory proposed by Gray (1970) that looks at the neurological factors that seem to contribute to this personality dimension.
Gray (1970) found an interesting relationship between neurological factors and extraversion. The main differences between extraverts and introverts are that extraverts are less susceptible to fear than introverts. They simply seem to have a lesser innate ability to learn to anticipate negative events such as frustrating, painful or frightening events.
Therefore, extraverts show poorer aversive conditioning which is due to their general lower level of fear. As a result, extraverts are not as likely to learn from possibly dangerous experiences. This is why they are more impulsive in general. They simply do not perceive these dangers. In this context, dangers are perceived as potentially frightening situations that can humiliate (or punish) the individual.
More specifically, extroverts do not anticipate these potentially negative events, like introverts do: they are not as sensitive to the potential humiliating situations as introverts. Because of their lower level of fear, they engage in behaviours that are more impulsive.
Carl Jung (1923) was probably the first to write about introversion and extraversion. He suggested that everyone had an extraverted dimension as well as an introverted dimension, with one being more dominant than the other. This theory is based on the fact that people change their behavior in different situations, and even extreme introverts and extraverts do not always act according to their personality type.
The neurological difference between introverts and extraverts
Gray (1970) suggests that the brain structures that mediate the ability to anticipate negative states involve the medial-septal nuclei, the hippocampus and the orbital-frontal cortex. The hypothesis is that this fronto-septal-hippocampal brain area is somewhat different in extraverts.
In one experiment, rats were given the drug doium amorbarbitai, which decreases the activation of the specific brain areas involved. After having this drug injected, their emotional responses to frustration, i.e. frustration for not getting a reward, decreased accordingly.
Lesion studies have shown that those who get their frontal brain structures removed perform poorly on passive avoidance tasks. In other words, the frontal regions of the brain seem to play an important role in our inhibitory processes, such as reducing impulsivity.
Furthermore, lesions of the septal brain area in monkeys produce more extraverted behaviours. Pre-frontal leucotomy increases extraverted behaviour as well. Therefore, it seems that three different parts of the brain is involved in the extraverted behaviors, and there might as well be an interconnection between them.
The most crucial finding of this review (Gray, 1970) is that behavioural disinhibition (i.e., increased impulsivity) is the most fundamental behavioural change that occurs as a result of lesions of the frontal brain regions.
However, behavioural disinhibtion has only been reported to occur in some patients after prefrontal leucotomy, so it is somewhat inconclusive. These results only support the theory proposed by Gray partly. Therefore, we may say that Gray’s theory is not adequately tested or verified.
Another interesting finding (Funder, 2010) is that introverts respond more strongly to sour taste stimuli than extraverts. For this reason, one might think that they are more sensitive to stimuli than extraverts. It is possible that an overstimulation of the nervous system results in more avoidance behavior.