Deric Bownds at Mindblog reports on a paper by Koch et al. (here) The gist of it is that stepping backward (as opposed to forward) mobilizes cognitive resources. Thus, whenever you encounter a difficult situation, stepping backward may boost your capability to deal with it effectively.
We are used to viewing situations with the arrow pointing from the brain to the rest of the rest of the body. But it this case the arrow is pointing from a bodily movement to the brain. So an actor creating the scene of a mathematician solving a problem, might take a step back from the blackboard, mutter and rub his beard for a moment and then spring back towards the board to write in the next line of the solution. The step back stands for a snag in the solution, the mutter and rub stands for being lost in thought, and spring back stands for the eureka moment. It is assumed that it is the problem that makes the man step back.
The same idea of a reversed arrow also occurs in the reports of artificially made facial expressions affecting mood. Normally it is the mood that causes the facial expression but the opposite causal direction is possible. Ditto for posture.
In reality we are talking about three parts of the same brain: the part that moves the muscles, the part that perceives through the senses the behavior of some part of the body and the part of the brain that is involved in mood or thought. These parts of the brain probably act in concert for either direction of the casual arrow; they are probably connected by feedback loops; and the difference between the two directions would be small changes in timings and signal strengths. If stepping back and cognitive control happen together then they happen together.
Back to the actor pretending to be a mathematician we seem to recognize the convention but it is not done in a way that normally enters consciousness. We perceive another person’s thinking but are not aware of the clues we use to make that judgment.