Three Studies of HSPs Presented at the American Psychological Association

Originally published in Comfort Zone Newsletter: February 2008.

I promised in the summer 2008 newsletter to describe in the fall issue the research I and others presented at a symposium that was part of the huge annual convention of the American Psychological Association. Then I forgot in November. So here it is.

The first study below was described in the February 2007 issue, but I will summarize it again.

Study One: We Are Less Biased by our Culture

This was an experiment by Sarah Ketay, Trey Hedden, Hazel Markus, and John D. E. Gabrieli, along with my husband and me. The title of the presentation was “Attentional Processing Neural Independence of Culture in Highly Sensitive Individuals.” (Pretty high-falutin’, yes?) This study used “functional magnetic resonance imaging” (fMRI) to compare ten Americans of European Descent (AEDs) and ten East-Asians recently in the U.S. while they were doing two simple visual-spatial tasks. (The data from one person’s fMRI requires hours and hours of work to extract from the computerized images, so the numbers in these studies are always small, which makes finding significant differences actually much less likely.)

From past research we knew one task was easier for AEDs. It involves judging the length of a line while ignoring changes in the box around it. Being more individualistic, AEDs pay less attention to “context,” such as family or community. They ignore it even on a simple task like this one, where the context is only a box. Because the box does not distract them, they had to use less brain energy on this task of judging the line lengths.

The other, complementary task is judging the size of a box while ignoring the length of a line inside of it. Again, it was already known that this task is easier for those from Asian cultures, where people do consider context more. So as expected, their brains were less active while doing this task of comparing box sizes.

I know–it’s surprising that culture would affect something so basic, but the evidence of this using other methods is quite solid. What was new was demonstrating it using fMRI. So in the fMRI study, as predicted, each group exhibited greater brain activation (had to work harder) for their culturally non-preferred task. This difference in activation was specifically in areas associated with greater effort in attention and working memory.

However, in further analyses, this effect was dramatically and significantly different for HSPs. Whatever their culture, HSPs showed little difference in their activation during the two tasks. This difference for HSPs was statistically significant and remained so even when we took into account their gender, strength of cultural identity, degree of introversion, and score on a measure of neuroticism.

In other words, we HSPs seem to be less affected by biases caused by the culture we grew up in, even very subtle biases. I guess it also means that we are a bit more alike, whatever country we are from, since we see things more similarly than non-HSPs.

Study Two: We Respond Differently to Subtle Stimuli and Become Over Aroused Under Pressure (Surprise)

“Sensory Processing Sensitivity Correlates of Neural Activation during Perceptual Tasks” was presented by Jadzia Jagiellowicz, the graduate student working with myself and my husband on studies of the physiological differences between HSPs and non-HSPs. In this experiment 14 subjects were each placed in an MRI machine and shown photos that were either very subtly different, or else very, very subtly different, and asked them to decide whether or not the photo they were seeing was the same as the previous photo. These difficult distinctions were required in two conditions–one in which the task had to be done quickly and one in which it was done more slowly.

There were two important results:

1. Whether asked to do it fast or slow, when looking for the more difficult differences in the photos the HSPs showed more brain activation than non-HSPs in areas associated with “secondary visual processing.”
2. When forced to discriminate between photos quickly as well, HSPs had more “autonomic arousal” then non-HSPs.

Both of these results are exactly what we would predict: We are designed to detect subtle stimuli and we are more physically aroused by tasks that push us to the edge of our abilities. In fact, one way to interpret the results is that the non-HSPs did not even attempt the tasks.

Study Three: Our Brains Are Different Anatomically

The last study was titled “Are the Brains of Highly Sensitive People Different?”

It was highly exploratory because the method, voxel-based morphology, is so new. It uses MRI to compare brain anatomies by breaking each MRI down into tiny “voxels” or cubes. Then brains can be compared (by computer) to see if there are any areas that are the same anatomically for a particular group of people compared to other people.

In this case, 28 HSPs’ and non-HSPs’ brains were compared, and there were very definite differences between the two groups in one area, the right middle frontal gyrus. (It would have been a problem that if you compared enough tiny areas, there would be at least one difference between the two groups, somewhere–but this problem is always controlled for statistically when this method is used.) This area is associated with word recognition, pain, and awareness of whether what you do will bring you pain. Alas, so little is really known about the brain, especially this specific area, that one should not make too much of this description of the area. It may even serve different functions for different people or for HSPs in particular. All we can say at this point is that all or most HSPs appear to be built the same way in this one part of the brain.

So both the method and the meaning of these differences are highly exploratory. The important thing is that there were definite, substantial similarities among HSPs and differences between them and non-HSPs. These were found even when you statistically removed introversion and neuroticism from the analysis. That is, the difference was only due to being highly sensitive. By the way, Asian as well as European-Americans were in this study too, so we know this difference is found in both genetic groups.

So What Does It All Mean?

These studies mean that your trait is very real. I did not make it up and you did not imagine it. All of the subjects were normal Stanford students (smart and in other ways outstanding)–some were HSPs and some not. So the trait is, again, normal and not a disorder. We knew that, but we have to show that to others!