If I grab my right wrist with my left hand and try to write something I relax the musculature of the left arm and shoulder (excluding the finger flexors) almost reflexively. If I grab the left wrist with the right hand and try to write I still engage the musculature of the right arm in an effort to help the left hand to write. It is more efficient to disengage the right shoulder musculature but that is not my tendency.
I believe my left tongue has been disengaged most of my life in learning to speak. I can use the musculature of the left tongue in a different context to move food, swallow, and touch the teeth on my left all the way to the back but I think it assists the right in getting there.
I now experience the left tongue as a separate structure that can move on it's own. I would have assumed that it would have no real influence on my posture of the neck and head but it feels to have a tremendous input. Form following function