One minor fascination of mine that I wrote about in BLONDES is facial asymmetry. Asymmetrical facial features themselves aren’t so interesting — everyone, save a few supermodels, has one brow that’s a little higher than the other or cockeyed ears. But the asymmetrical expression of feelings is interesting, and it turns out that there’s some real science to it.

Scientists have long known that the right side of the face is controlled by the left hemisphere of the brain, and the left side is controlled by the right hemisphere.

Why does this matter?

It means your left side gives away more about your state of mind than your right side. The right hemisphere of the brain is more “emotional” and, because it controls the left half of your face, raw emotions leak out more on the left than the right. Numerous studies have found evidence for what they call “right-hemisphere dominance” and “lateral symmetry of bodily emotion expression”. For instance: People who are emotionally expressive, particularly women, are inclined to turn their heads right, baring more left cheek. Artists tend to paint the left profile of their subjects, especially if the subject is a woman. The leftward bias, the researchers suggest, draws out more of the sitter’s true self. Portraits of powerful men, however, are commonly painted with more right cheek exposed. (Visiting an art museum the other week, I noticed this was true.) A recent study also found that the entire left body side expresses higher amplitude and energy than the right, resulting in higher expressiveness. Next time you find yourself gripped by feelings, be aware of which side of your body is more active.

Some studies suggest that negative emotions in particular are expressed on the left side of the face more than the right. (Note that artists’ renditions of a two-faced Dr. Jekyll/Mr. Hyde here , here, here, here, and here always show Hyde as the left half of the face. Never is the good, rational doctor depicted on the left.)

When deciding which snap to use for my author photo, I was keenly aware of the difference between the left and right sides of my face. I hated the shots that showed more of my left profile. I looked too testy or too tentative; something was off. Friends disagreed, finding the left-biased portraits more charming and authentic. But I resisted and chose one with maximum right cheek — and felt more in control.