Every day our face produces thousands of expressions. Some of them reflect what we actually feel, and some of them are meant to make a desired impression on other individuals.
These two types of facial expressions are controlled from two distinctly different areas of the brain: the emotional center (limbic system) and the volitional center (motor cortex).
Limbic system is the “factory of emotions”. It works the same way in all animals, humans included. Once we experience an emotion, it is immediately reflected either by our facial expression, or by the body language, or (most of the time) by both. It is an evolutionally much older formation that works the same way in all human beings. We can unmistakably recognize joy or surprise, curiosity or anxiety, anger or disgust by just looking at someone’s face, and it does not matter to which race or sex that person belongs.
Motor cortex exerts a volitional control over our facial expressions. This ability had only developed in humans at the later stages of evolution, when personal interactions gained importance for the social status and the survival of an individual.
Nucleus of the facial nerve summates the signals arriving from both centers, and our face reflects the result. We can, for example, suppress our joy if the smile in particular circumstances would be inappropriate, or can conceal our disappointment behind an artificial smile if the situation so dictate.
The limbic system is capable of producing an extremely fine-tuned and highly differentiated control over facial muscles, because we experience (and need to reflect) an extremely diverse spectrum of emotions.
The control over facial movements by motor cortex is much coarser and much less nuanced. Very often we can distinguish a genuine smile from the forced one, and a real surprise from its artificial copy. We subconsciously notice the difference.
Ironically, after Bell’s palsy we engage only our motor cortex while trying to produce some facial movements, because we can consciously control the intensity of contraction signals. The intensity of emotional expressions depends only on the intensity of the experienced emotions and cannot be consciously controlled.
No wonder that after the long-standing Bell’s palsy we develop synkinesis, mass movements and other complications that result naturally from the “habitual overdose” of volitional efforts.
– Alex Pashov
Crystal Touch Bell’s palsy clinic