In the 1920s, psychologist Carl Jung conceived that introverts focus on the mind’s contents (alone-time) and extroverts focus on external objects (community, social gatherings).
Introversion was mistaken as shyness for a long time, but with recent awareness, most people now know that introversion is a ‘preference’ while shyness comes out of distress.
The preference, however, is not merely psychological; our physiology (the way our body parts function) has a significant role to play.
We are born with a brain component that decides whether we will favour introversion or extroversion.
That component is called Ascending Reticular Activating System (ARAS); it is a part of the brainstem, which connects our brain to the spinal cord.
ARAS is like a hollow pipe, and it is responsible for supplying stimuli (things or thoughts that trigger action) to the brain so that the brain remains awake.
In introverts, this hollow pipe is much broader than in extroverts.
So, very little stimulus and effort are required for the ARAS to kick the brain into an action-state; in extroverts, ARAS is narrow, so it has to suck in a lot of stimuli to keep the brain wakeful.
In research, it was found that introverts salivate more than extroverts in response to a drop of lemon juice because of increased activity in ARAS, for which food is also a stimulus.
Too much stimulation, therefore, leaves introverts exhausted, while extroverts want the party to carry on for a ‘bit’ longer.
But ARAS explains only a part of the reason; the other part is the environment.
Research conducted on twins suggests that physiology contributes between 39% to 58% to a person being an introvert or extrovert; the remaining is determined by the environment.
However, the family environment that the twins share is far less important than individual environmental factors that are not shared between siblings.
The defining importance of our brain design in this classification is also established because introverts have higher blood flow in brain areas, which are responsible for planning & problem-solving.
On the other hand, extroverts have more blood flow in brain areas, which experience sensory and emotional experiences.
