A Good Joke For a Good Smile--Stroke And Emotional Smiles

If you know someone whose face is paralyzed on one side because of a stroke, you might be under the impression that his or her smile, as you knew it, is gone forever. Not so. It is true that when a stroke affects the area of the brain that controls facial muscles, the movements of these muscles are profoundly impaired on the affected side. However, this is only true for movements that are initiated voluntarily. Movements initiated as a part of an emotional state, such as during a natural smile, are completely preserved.

How can this be? Voluntary movements of the face originate in the "face area" of a part of the brain called the motor cortex. Cells in this area send long connections to a different area of the brain which harbors the very cells that control muscles in the face. This other area is called the facial motor nucleus. Thus, when you smile voluntarily, like you do when you are smiling for a picture, cells in the "face area" of the motor cortex send signals to the facial nucleus, which in turn send signals to the muscles in the face, causing them to generate a smile.

What is really interesting is that emotionally-driven smiles are initiated from an entirely separate area of the brain called the cingulate cortex. This area forms part of a larger complex of the brain collectively called the “limbic system”, which processes emotional information. As long as a person suffers a stroke that spares the connections between the cingulate cortex and the facial motor nucleus, that person should still be able to generate emotional smiles.

If you know someone whose face appears partly paralyzed after having a stroke, you should know that it is possible to enjoy their full smile, just like you did before they had a stroke. Their smile is still there waiting for you to unleash it, perhaps by a funny joke or story.

Recommended reading:

Antonio Damasio, Descartes’ Error: Emotion, Reason, and the Human Brain, Penguin Books, New York, 2005