Elaine Aron refers to her discovery of the “highly sensitive person” as that of “Sensory processing sensitivity,” and her husband designed a Highly Sensitive Person (HSP) scale in order to assess the degree of sensitivity in individuals.
She makes the careful point that being a highly sensitive person is not the same thing as being either introverted or neurotic, noting that 30 percent of highly sensitive people are extroverted, and not all introverts are highly sensitive, although she does note that high sensitivity is highly correlated with the personality trait of neuroticism. Around 15-20 percent of the population is highly sensitive, and the trait is equally distributed between the sexes.
The highly sensitive person does tend to exhibit higher degrees of neuroticism if he or she has a difficult childhood. Those with better childhoods exhibited no more neuroticism than others, however; indeed, it is possible, she notes, that they are actually better adjusted than others, almost as though they were more easily molded by their environment than others. In the case of the HSP with a neurotic temperament, the inability of others to understand their personality, she notes, disturbs them even more.
She criticizes studies which she believes place an inordinate degree of emphasis on the extent to which neuroticism is an innate trait of the HSP, arguing that many studies need to focus more on the environment in which the individual was raised than they have done in the past.
One study she cites studied high sensitivity in rhesus monkeys, and found that their brains contained less serotonin, thanks to a genetic variant, suggesting a correlation between low serotonin and the coexistence between high sensitivity and neuroticism. She notes that comparable genetic variants are responsible for low serotonin which makes us more vulnerable to stressors, further lowering our serotonin and placing us in a vicious cycle of stress.
She furthermore suggests that studies attempting to correlate low serotonin with depression yielded inconsistent results because those with low serotonin who were nonetheless non-neurotic had better childhoods; another critique of a naive biological determinism.
Indeed, those with this genetic variant responsible for llower serotonin improves decision making, memory and cognitive function in general. It may even confer greater mental health when paired with helpful life experiences. She notes that highly sensitive rhesus monkeys who had better environments exhibited greater social dominance and resilience to stress.
Far from being limited to humans and rhesus monkeys, the phenomenon of being highly sensitive, she notes, can be found among certain fish and even fruit flies. Those species which contain highly sensitive individuals numbers over 100.
She suggests the reason for its prevalence has to do with the adaptive value of being highly responsive to one’s environment when it comes to detecting potential threats from the environment. The highly sensitive person is also more sensitive to mistakes, and more likely to retain their consequences and learn from them in future situations. She notes that biologists refer to “responsivity” (their word for sensitivity) as a trait which helps individuals remember their environment better than others do, and thereby predict the future better. In short, they are better at induction.
Unfortunately, the adaptive function of high sensitivity can malfunction, causing us to obsess over negative experiences, she notes, and engage in negative over-generalizations. This can contribute to the nervous system overload to which the highly sensitive person is prone.
Furthermore, she argues, high sensitivity is genetic. As noted before, high sensitivity is linked with a gene which controls the amount of serotonin in the brain. However, dopamine is another neurotransmitter important in mediating the trait of high sensitivity.
She cites Chinese researchers who found 10 variations of 7 genes associated with dopamine levels. Rather than there being a single “sensitivity gene,” therefore, sensitivity is polygenic, or the result of the contributions of numerous genes.
She claims to have inferred the existence of sensitivity from the work of the psychologist Jerome Kagan, who referred to it as “inhibitedness.” Furthermore, contrary to the tendency to want to view traits on scales or spectrum, Aron makes the bold claim that sensitivity is an all-or-nothing deal. You are either highly sensitive or you are not.
Aron, Elaine (1996-06-30). The Highly Sensitive Person . Citadel. Kindle Edition.