Micro expressions are fleeting facial expressions that occur when some people try to repress or suppress an emotion. If they are unable to do so completely, the emotion may flash onto the face very rapidly, sometimes for as short a time as 1/125th of a second. Although most of us miss most of these fleeting expressions, about 85% of people can improve their micro expression recognition ability with training. (http://www.paulekman.com/mett.html
Micro expressions tell you a lot about a person's emotion. Whether they tell you that a person is lying is another matter.
A micro expression suggests that someone may be trying to conceal an emotion and correct recognition of the micro expression tells you what that emotion is. The emotion may or may not be related to a lie.
For example, a fear micro might appear because the liar is afraid she will be caught in her lie. But an innocent person might be also afraid - that her truth will not be believed. And the fear could be totally unrelated to truth or deception. It might have just popped into her head that she didn't turn off the gas stove when she left home several hours earlier.
Micro expressions tell us what a person is feeling, but not why they are feeling it. Interpreting the emotions of others, knowing why they are feeling what they are feeling, is necessary for accurate lie detection.
In a recent TV series, "Lie to Me," when a relevant micro expression appears the characters in the show instantly declaim "He's lying!" Unfortunately, this suggests that lie detection is easy once you master micro expression recognition. Expert lie detectors will tell you: It ain't necessarily so. Experts use micro expressions (in addition to other clues) as an indicator that something may be amiss. Then they seek further information before calling someone a liar.
So micro expressions DO communicate a great deal about emotion, and MAY communicate information about deception.