July 30, 2003 -- Fear is written in our genes, a new study suggests.
One way we learn to be afraid is by fear conditioning. Say you see a picture of a triangle and, at the same time, get a painful electric shock. The next time you see a triangle, you feel fear. That's fear conditioning.
Different people respond to fear conditioning in different ways. That's important because fear conditioning is related to the way anxiety disorders seem to develop. Could there be a genetic basis to how people learn fear?
Maybe so. After all, people can be more easily taught to fear pictures of dangerous things -- snakes and spiders, for example -- than to fear pictures of harmless circles and triangles. This suggests that some fears, at least, are coded in our DNA.
If so, identical twins might hold the answer. Identical twins have exactly the same genes; fraternal twins are as genetically different as non-twin siblings.
Virginia Commonwealth University researcher John M. Hettema, MD, PhD, and colleagues looked at 90 pairs of identical twins and 83 pairs of fraternal twins. Each was shown a picture of a spider, a snake, a circle, and a square. Sometimes one of the pictures came with an "uncomfortable" electric shock. The researchers measured the twins' biological fear responses during all phases of this fear conditioning.
The result: Identical twins were much more likely to react in the same ways to fear conditioning as fraternal twins. Between one-third and one-half of the fear conditioning process appeared to be inherited.
"Now we can say that the fear conditioning process in humans is controlled, at least to some extent, by genetic factors," Hettema says in a news release. "Understanding fear conditioning provides one aspect of how humans develop anxiety symptoms, which could lead to better treatments for these chronic illnesses."
The findings appear in the July issue of the Archives of General Psychiatry.