A series of ground-breaking longitudinal studies conducted by developmental psychologist Dr Jerome Kagan, suggests that introverts are born, not made.
An ongoing study, begun in 1989 by Dr Kagan, documenting the temperamental and physiological characteristics of a group of children from infancy right through to adolescents has provided clear physiological evidence that a subset of infants as young as 4 months old, are capable of displaying stronger responses and therefore stronger levels of awareness, known as ‘hypersensitivity’, toward external stimuli, than other infants of the same age.
After observing and measuring the emotional and physiological responses (heart rate, blood pressure and other physiological indicators related to the amygdala), of 500, 4 moth old infants to new and unexpected sights, sounds and aromatic stimuli, Dr Kagan predicted that the 20% of infants within his study who responded to the stimuli by showing signs of ‘hypersensitivity’ or ‘hyper awareness’, would, most likely, become introverts.
Dr Kagan’s hypothesis centered on his theory that introverts are people who are keenly aware of, and therefore more profoundly impacted on, by external stimuli.
The higher the degree of ‘hypersensitivity’ an individual experiences towards sights, sounds, smells, and the closeness of other people, the more likely it is that those same individuals will seek to avoid them.
Hypersensitivity both creates and explains why introverts hold such a strong preference for seeking out quiet, serene and unpopulated spaces in which to live and work.
Accordingly, Dr Kagan surmised, the more awareness and responsiveness towards external stimuli an infant demonstrates, the more likely it is that the infant is showing signs of ‘hyper-awareness’ and ‘hypersensitivity’ toward their environment.
Hence those infants who respond the most robustly when introduced to new stimuli, were according to Dr Kagan’s initial hypothesis, also the most likely to become introverts. But was he right?
Over the course of the following years, Dr Kagan met with and studied the responses of the same initial infants as they grew. At the ages of 2, 4, 7 and 11 years, the children returned to Dr Kagan where they were once again exposed to new and unexpected stimuli in the form of events and people.
As Dr Kagan had predicted, those who displayed the highest degrees of physiological and emotional hypersensitivity towards external stimuli as infants, had indeed grown into quite, reserved and thoughtful individuals whilst those who responded the least to the same external stimuli, had grown into relaxed, outgoing and gregarious individuals.
But what made Dr Kagan think that there may be a connection between hypersensitivity and introversion in the first place?
His scientific background provides the explanation behind both his initial hypothesis and his decision to measure the key sets of physiological responses that he and his team recorded, which all link directly back to an area inside the brain called the amygdala.
One of the key areas of scientific interest surrounding the amygdala is its connection to our ‘fight or flight’ responses. It is the amygdala’s job to send out the messages to our nervous system that trigger our ‘fight or flight’ responses.
The amygdala quite literally controls whether or not we will feel safe and secure or scared and threatened, when exposed to new or unexpected stimuli.
The more highly reactive our amygdala becomes, the more likely we are to feel threatened and become hyper vigilant, when confronted with new situations. This means that those with hyper sensitive or highly reactive amygdala’s are more likely to exhibit other symptoms of discomfort when confronted with new situations including increased heart rate, tightening of the vocal chords and having their bodies flooded with the stress hormone cortisol.
This combination creates an overwhelming sense of nervousness, anxiety, discomfort and fear in those individuals who experience it.
These are exactly the same physiological and emotional markers measured and observed by Dr Kagan within his longitudinal study of infants.
Dr Kagan therefore successfully linked hyper activity within the amygdala to the responses of hyper sensitivity observed within a subset of infants, during exposure to external stimuli. Given that his initial hypothesis was that he could predict, via their responses, which infants were more likely to become introverts, he also linked the key features of introversion to both hyper activity within the amygdala and hypersensitivity toward external stimuli.
In doing so, Dr Kagan found a direct correlation between biological response and social response which indicates that the origin of introversion is biological and not, as had been previously suggested, social, cultural or psychological.
Introversion is therefore the result of nature not nurture. Not a taught response but a biologically driven, natural one.
Dr Kagan’s study not only significantly highlights the need for our society to extend its understanding of the biological mechanisms of introversion, but also the need to be aware that an individual’s predispositions towards introversion should no longer be being viewed through the lens of wither wilful ‘choice’ or ‘personality type’.
His study clearly indicates that introverts are not people who simply ‘choose’ to live ‘far from the maddening crowd’, but rather are a legitimate subset of the population who experience a very real, biologically driven aversion toward our over crowded, over-stimulated, 24/7, modern-day society.
As such, introversion needs to be understood as a hardwired, physiological and naturally occurring set of neurodivergent responses toward external stimuli, as experienced within a subset of the population.
Introversion should be seen as a legitimate way of being and introverts viewed as people who, like everyone else, are striving in their own ways to flourish and succeed within a world that constantly offers up additional challenges, due specifically, to their unique way of being.
Therefore, introversion should be viewed as being yet another variation within the vast array of neurodivergent conditions, right alongside Autism, which serve to make up the spectrum that is, the human condition.