But how does the brain achieve both types of smiles using the same facial muscles? It all depends upon which part of the brain starts the smile.

　　If the brain's dopamine neurons (多巴胺能神经元) start the smile, then the smile looks sincere. If the brain's motor cortex starts the smile, in other words, if we are consciously willing ourselves to smile, then a slightly different set of facial muscles are actirated. It can be difficult to describe precisely how real and fake smiles differ, but we are all very capable at knowing the difference.

　　But can forcing yourself to smile produce the same kinds of good feelings as a real smile does?

　　Anything that prompts the release of dopamine in the brain brings pleasure.

　　For example,

　　cocaine and coffee both release dopamine in the brain.

　　The release of dopamine in the front half of our brain is accompanied by a real smile. But can this process be reversed? What about putting on that happy face? Can the simple act of smiling bring pleasure? Yes.

　　When we smile, fake or real, the contraction of the facial muscles slightly distorts (扭曲) the shape of the thin facial bones. This slight distortion in their shape leads to an increase in blood flow into the brain and then increases the release of dopamine.

　　As a result, walking around all day with a smile on your face will make your mood happier. Not only will you be happier but your smile might lead to the release of dopamine in someone else's brain—now that truly shows the power of a smile.

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