Smile, and the whole world anticipates it

From Medical Express:

Smile and the world smiles with you—but new research suggests that not all smiles are created equal. The research shows that people actually anticipate smiles that are genuine but not smiles that are merely polite. The differing responses may reflect the unique social value of genuine smiles.

"These findings give us the first clear suggestion that the basic processes that guide responses to reward also play a role in guiding social behavior on a moment-to-moment basis during interactions," explains psychological scientist and lead researcher Erin Heerey of Bangor University (UK).

The fact that we anticipate real smiles plays to my hobbyhorse that, during social interaction, we are coupled with one another in the same temporal framework. 

Here's the full abstract of the original article, Predictive and Reactive Mechanisms in Smile Reciprocity, published by Erin A. Heerey and M. Crossley in Psychological Science:

During face-to-face interactions, people reciprocate their conversation partners’ genuine and polite smiles with matching smiles. In the research reported here, we demonstrated that predictive mechanisms play a role in this behavior. In natural interactions (Study 1), participants anticipated a substantial proportion of genuine smiles but almost no polite ones. We propose that reinforcement-learning mechanisms underpin this social prediction and that smile-reciprocity differences arise because genuine smiles are more rewarding than polite smiles. In Study 2, we tested this idea using a learning task in which correct responses were rewarded with genuine or polite smiles. We measured participants’ smile reactions with electromyography (EMG). As in natural interactions, people mimicked polite smiles reactively, after seeing them appear. Interestingly, the EMG data showed predictive responding to genuine smiles only. These results demonstrate that anticipating social rewards drives predictive social responding and therefore represent a significant advance in understanding the mechanisms that underpin the neural control of real-world social behavior.

So, reward vs. not. OK. But that doesn't quite get to the temporal issue.

It seems to me that what's going on is that this type of social interaction is mediated by two loosely coupled behavioral systems. One of those systems enters into synchronized coupling with other actors. That's the one that generates the genuine smiles. The polite smiles are generated by the other system, which is not intersubjectively coupled.

We know, in fact. that the facial muscles are controlled by two different neural systems. From Beethoven's Anvil (p. 98):

Imagine you are in some public place and you receive bad news, perhaps about the death of a loved one. You are stricken with grief and feel a strong impulse to cry. At the same time you feel a contrary impulse to remain reserved in public, to suppress the sobbing and the tears. Later on you are called upon to deliver a eulogy at the funeral. Once again you are torn. In order to speak intelligibly you must remain in control of your vocal apparatus. But you are speaking of your dead friend and so are also moved by a grief that wants to commandeer the same muscles in the service of crying out. 

This is not an unusual situation, nor is grief the only occasion for such conflict. Laughter, anger, and physical pain can also generate impulses we struggle to suppress. What are the parties to this conflict? They must be inside us, in the nervous system, but where? 

The impulse to cry, or laugh, or shout in anger, arises in subcortical structures and acts on the muscles of the trunk, respiratory system, vocal system, and face through one set of pathways. The impulse to block such expression arises in cortical structures and acts on the same muscles through different, though often physically contiguous, pathways.

If you're curious about the neuroanatomy of smiling, check out the facial nerve and smile surgery, which is done to restore expressive mobility to the mimetic muscles (yes, that's what they're sometimes called) of the face.