Very interesting. I have MS which causes destruction of myelin. That finger tapping test is part of a regular neuro exam. I can tap my finger on one hand, just fine, but on the other hand, the finger tapping is erratic, gets slower toward the end of the ten seconds, and not rhythmic at all...obviously because I have lesions affecting one side but not the other.
Sorry to see you have MS and hope you find something to alleviate it.
Can you tell us what is that tapping test? A rapid tapping for some time period?