I think we all understand that it is practically an instinct to touch someone to offer comfort when they are in pain.  Now, researchers at the University of Haifa and the University of Colorado-Boulder have found that holding hands synchronizes electrical brainwave activity and causes a reduction in pain.  The study, reported in Science Daily and published in the Proceedings of the National Academy of Sciences, found that merely being in the presence of a romantic partner created some synchronization but that physical touch through holding hands had the strongest effect in both synchronization and perceived pain reduction.  Check out a summary of the research at Science Daily.

A handful of neurofeedback practitioners around the world have also been experimenting with training electrical brainwave activity in couples to increase synchrony and thereby increase feelings of connectedness.  I haven’t seen published research on their results yet but have read anecdotes that this work is promising.

https://www.sciencedaily.com/releases/2018/03/180301094822.htm