One of the mysteries I've ruminated about for many years is the scene - usually from some movie - where two people - most memorably young girls who are, after all, alien creatures to me - make a pact with one another. It's a multi-step process involving escalating verbal confirmations of intent to keep the agreement, with a great deal of intent gazing and facial expressions, often ending in a ritual entwining of the little fingers of the right hand - the pinky promise - which is represented as some sort of ultimate and inviolable act of commitment.

As a rough boy, a bad boy, I could never understand much less make a pinky promise, except perhaps with a girl and then it would be meaningless since I had no idea how the pact was actually sealed. It was obviously not the mere act of finger entwining, there was some sort of mind meld involved and I lacked the art.

The formal definition of the pinky promise is unsatisfying, and a bit grim.

Traditionally, the pinky swear is considered binding and tantamount to a handshake in terms of sealing a deal. The pinky swear originally indicated that the person who breaks the promise must cut off their pinky finger.[2] In modern times, pinky swearing is a more informal way of sealing a promise. It is most common among school-age children and close friends. The pinky swear signifies a promise that cannot be broken or counteracted by the crossing of fingers, the "I take it back" or any similar trickery.[3] The Pinky Swear can be broken if all parties agree. Pinky promises are also only valid if all parties agree prior to interlocking pinkies. A pinky swear can however be broken if the majority of candidates chose to break it.

OK, so loss of a finger is a serious commitment, but my current best understanding is that it is the information revealed to one another - by some still mysterious method - during the promise ceremony that is the heart of the matter, and there may be a science to measure the phenomenon.

Despite the ubiquity of promises in human life, we know very little about the brain physiological mechanisms underlying this phenomenon. In order to increase understanding in this area, neuroscientist Thomas Baumgartner (University of Zurich) and economists Ernst Fehr (University of Zurich) and Urs Fischbacher (University of Konstanz) carried out a social interaction experiment in a brain scanner where the breach of a promise led both to monetary benefits for the promise breaker and to monetary costs for the interaction partner. The results of the study show that increased activity in areas of the brain playing an important role in processes of emotion and control accompany the breach of a promise. This pattern of brain activity suggests that breaking a promise triggers an emotional conflict in the promise breaker due to the suppression of an honest response.

Furthermore, the most important finding of the study enabled the researchers to show that "perfidious" patterns of brain activity even allow the prediction of future behavior. Indeed, experimental subjects who ultimately keep a promise and those who eventually break one act exactly the same at the time the promise is made – both swear to keep their word. Brain activity at this stage, however, often exposes the subsequent promise breakers.

My emphasis. I think that this is mistaken. They don't act quite the same and those with sensitive and well used social readers - i.e. the young girls mentioned above - can detect such brain patterns during the intent gazing part of the ceremony.

Those of us with less effective social readers may at long last have a prosthetic device to help overcome our limitations. One day, perhaps not too long from now, we may be able to don some sort of head gear wired to truth devices which will reveal perfidious intent, even if it isn't consciously known to the chronic liar making false promises.