Up to 20 percent of the population exhibits a trait that sets them apart. Scientists are finding out why.
Psychologist Elaine Aron has pioneered the study of a category of human personality that is generating considerable buzz both in the media and in the scientific community: the highly sensitive person (HSP). People in this group look the same as everyone else, but they don’t respond to the world the same. The way they think, work, feel, and even love is distinctive. Tendencies like acute awareness of emotions, heightened response to loud noises and other stimuli, and the deep processing of information are all things that set HSPs apart.
Want to know if you’re an HSP? Take this online test developed by Aron and her husband, a fellow psychologist. Aron reckons that up to 20 percent of humans on the planet are highly sensitive, a trait that is found in animals, too. I spoke to Aron about what science has to say about HSPs, and how understanding how their brains are encoded may help society to better accommodate these people and make use of their considerable gifts.
Lynn Parramore: Research suggests that some people are genetically predisposed to high sensitivity. What scientific methods have been used to investigate?
Elaine Aron: There are two studies. One used was the more common method of looking for an association between a genetic variation and a personality trait. That is to take one candidate gene that we think is important for the personality variable; in this case, sensitivity. The candidate gene was a variation in the serotonin transporter gene, what is called the short-short variation, which refers to two short alleles, as opposed to one short and one long, or two longs. The short-short variation had been inconsistently associated with depression and other problems. It was seen as creating vulnerability. But many people with this genetic variation are not depressed, so researchers began to question their understanding of it, and found in numerous studies that it actually bestows many advantages. It only caused trouble when carriers had had a stressful or unsupportive childhood, or else, in some cases, were immersed in stressful life events.
This led, along with some other studies, to the whole subject of what is called differential susceptibility. People with this gene, or with certain behaviors, such as cautiousness or physical or emotional reactivity —all signs of sensitivity — do better than others in good environments and worse than others in bad ones. That’s an important concept for us. It’s mostly been studied in children, and if they have grown up in a supportive environment or there’s an intervention to help their parents raise them, they actually turn out better than other children in social competence, academic performance, health — all kinds of variables have been looked at. It’s becoming a very popular thing to study. If children don’t have that supportive environment, then there’s depression, anxiety, and shyness and all of that. So sensitivity does not lead to vulnerability. It leads to differential susceptibility.
In the meantime, in China, some researchers were looking at sensitivity that other way, by looking at many genes at once to see which ones if any are associated with the variable of interest, in this case sensitivity. They chose high sensitivity because until then studies were finding unexpectedly low associations between genes and personality traits, such as introversion or neuroticism. That was surprising, because we know that a large percentage of personality overall is contributed by genes. We know that from comparing fraternal and identical twins. But we didn’t have a name for what those traits were that were encoded in the genes.
So these people in China looked at my Highly Sensitive Person scale and said, well, this seems to be deeply rooted in the nervous system. So they did the entire genome mapping of anything to do with dopamine. There are quite a few different dopamine genes, and they boiled it down to seven. And these gave a result more like what one would expect, given that we think personality is partly encoded in the genes. So what we are describing as high sensitivity is probably close to describing something that is actually genetically coded, in this case in seven variations of genes affecting the creation and transportation of dopamine.
We don’t know yet how those dopamine genes affect behavior. They’ve never come up before as being important for personality. These genes may reduce dopamine, or use it in a particular way that’s unusual. So the point is sensitivity is probably created by a number of genes, perhaps tending to be inherited together as a group. Or it may be that sensitivity has evolved along different routes, because if it’s a survival strategy — and it’s been found in over 100 species and probably exists in more —it may have landed in our species through several routes. Or there may be slightly different kinds of sensitivity, but not so different that the HSP scale [the test developed by Aron and her husband] doesn’t tap it.
LP: What evolutionary benefits might be associated with having this trait?
EA: Max Wolf, a scientist in Europe, did a computer simulation that did a very nice job of explaining why sensitivity had an evolutionary advantage. We knew that it had to because it’s found in such a large minority of people, 20 percent. It would have been eliminated long ago, or it would have been found in only a very small percentage of people, if it had no advantage.
Wolf did a computer simulation, kind of like a game, in which you had the choice of either noticing everything in every situation you encounter and using that information in the next situation you encounter, or basically assuming that your next encounter will be nothing like this one and not bothering to notice anything at all. In many situations, the next situation has nothing to do with the previous one at all. Other times there is a relationship. The simulation also assumes, rightly, that there’s a certain cost to having the more complicated nervous system of a sensitive person or a cost to using energy for paying attention to things.
So there has to be a payoff at the other end. Manipulating the payoffs and the costs in various ways demonstrated that it didn’t require much to make it pay to be highly sensitive.
But Wolf also made the interesting observation that the game doesn’t work if everyone is sensitive. His analogy is if there’s a patch of good grass, and every animal noticed it or smelled it or however they find it, then it wouldn’t be any advantage to any individual to carry this genetic variation. I joke that if I’m in a traffic jam and I notice a shortcut, it’s only useful to me as long as nobody else takes it. If all the other cars notice me turning and they follow me, then there’s no advantage to my noticing another way. There is now just as much traffic on my route as the other routes. The point is that we [HSPs] are invisible for a reason. All of us aren’t skinny. All of us don’t have curly hair or we’re not all left-handed or something that would make it easier to identify us.
Many people have thought about how it’s helpful to a particular species to have this trait. I think it’s kind of obvious in humans that some people spend more time reflecting — I use the term DOES: these people exhibit depth of processing (D), they are easily overstimulated (O), emotionally reactive and empathic (E), and sensitive to subtle stimuli (S). The only disadvantage is being overstimulated, which is the cost to us of being highly sensitive. But the rest of it has benefits. Yes, being emotionally reactive can be difficult, but it actually helps to motivate a person to think more!
LP: What implications does the science have for people who are highly sensitive?
EA: In the short run, HSPs need to see the research in order to believe the trait is real. Believing it is real can be difficult, because it is invisible and because the majority don’t have it, so we often grow up thinking, well, I should be behaving like everybody else. Or I shouldn’t be overstimulated right now. No one else is. I don’t know why I’m so tired. Why do I notice these things that other people don’t? Gee, I really have this great idea but nobody else really gets it. I’m pretty sure we should do this but nobody else seems to see why. Should I insist? No, I won’t, because I don’t want to make people mad. Now it turned out to be a mistake, and I knew it would be a mistake. So all of that self-talk makes us squash our sensitivity, especially men (there are equal numbers of highly sensitive men and women), and maybe not even think we have the trait.
Then when you also look at the research on the brain functioning, where we find that sensitive people have more activity in the neurons that have to do with empathy and just general consciousness, then we say, oh well, that’s not a bad thing to have.
The research also helps in a larger way, to help the rest of the world appreciate that the trait is real and has value. Most HSPs really do blend in, but a few with more problems—depression, anxiety, low self-esteem, health issues—are often the ones others notice, so that they think this is all there is to sensitivity. In fact, the majority is doing very well. I’m hoping that the research empowers sensitive people to be more themselves so that everyone can benefit from that — employers, spouses — everyone.
I’m also hoping that the research will help parents and teachers and pediatricians and also employers and policy-makers to create conditions that bring out the best in sensitive people because we see their differential susceptibility and we see how unusually well they can function in a good environment, and not so well in a bad one.
LP: What further research is needed for scientists to understand more about highly sensitive people?
EA: Well, with the children there has been considerable physiological research, but less of that has been done with adults. It might be interesting to see how sensitive people react in certain situations. Certainly we want to study the kinds of interventions that work for best for them. If they’ve had an unsupportive childhood, how can we alter the effects of that — in adolescence or whenever we can apply an intervention?
In terms of the brain studies, anatomical studies aren’t that helpful — looking at whether HSPs’ brains look different. What brain researchers look for is how do brains look different when they are doing a particular task. So we’ve given sensitive people and non-sensitive people a few tasks while having a brain scan (this is called functional magnetic imaging), but there are quite a few more that we could do.
Another interesting study would be would be to look at rejection or shame. We know the part of the brain that reacts to rejection or shame. We know that it’s the same part of the brain that reacts to pain. When we say someone has “hurt” feelings, we are literally talking about how it hurts in the brain. I’d like to see if that area is more easily stimulated in sensitive people, by subtle indicators. That would probably be helpful for seeing that this is normal for HSPs. Because when we do studies like this, we control for negative affect like depression or anxiety. So even if a person had a bad childhood, we’re sort of saying, OK, we’re going to take that piece out of your scoring on the test and then the brain scan and we’re going to see if you’re still that way in spite of taking that piece out.
If all sensitive people are more easily shamed than others, and I think they are, it would make evolutionary sense. We wouldn’t bother to study for a test if we weren’t afraid of being shamed for failing. So shame is another motivator. I want to do it right so that I’m not embarrassed or I don’t look stupid. Again, it makes sense that for a person to think deeply or notice subtleties, they would have to have emotional motivation of some kind to process things more carefully.
There are many other studies that could be done. I think it would be interesting to explore more how sensitivity is viewed in different cultures and different subcultures. Some has been done about this for men, but in general. The possibilities are vast, because this trait seems to affect almost all aspects of behavior in some way. I even did a survey study of HSPs and non-HSP regarding their sexuality, and of course there were differences in what they liked and didn’t like, what life experiences they had had in this realm. The trait affects every sort of attitude and behavior.