BERLIN — People constantly touch their faces. They stroke their chins or eyebrows, rub their noses or ears, cover their mouths or throats. We find it normal because everybody does it, but what does it mean?

Animals only touch themselves if there is an apparent reason to do so — for example, if a pesky insect is bothering them. Apes are the only exception. They too touch their faces, and anybody watching them would be unable to discern why.

This fact has puzzled scientists for over 200 years, mainly because the amount of touching increases when people or apes appear to be under stress.

Brain researchers working with Martin Grunwald at the University of Leipzig have succeeded in solving the puzzle. In the journal Brain Research, they report on many years of experimentation during which they analyzed the brain's electrical activity shortly before and after spontaneous face touching.

They discovered that touching changed electrical potentials in the brain, namely those having to do with storing information in working memory and emotional condition.

Shortly before touching the face, these parameters decreased. That means that working memory was overloaded, which is paired with a feeling of emotional overload. But after research subjects touched their faces, the parameters increased again.

Their conclusion is that spontaneous face-touching helps to regulate cognitive overload and stress. This "self-stimulation," as the Leipzig researchers call it, balances out disturbances in processing information and emotional swings.

What is still unclear is just why touching our faces has these particular effects.