Well said, Peggy and Jean.
If you sign up for a study and change your mind later, you are not committed to participate to the end of the study.
When I had a unilateral DBS/STN done in '06, I allowed my NSU to insert a new designed lead (multi contacts)and "play around" with it before they put in the approved lead. They also put a hot wired glove on my affect hand and play video games while in the operating room. Also requested that they call my husband from the OR to have a cold margarita waiting for me when I got back to my room. They did but my husband didn't.

There is now apparently a new multi contact lead out there - the source I would have to look up. Unfortunately, DBS precludes you from most studies.
TG