Banjo player Eddie Adcock had been having trouble with a neurological problem causing a tremor in his right hand which interfered with his playing. So when brain surgery was performed to try and control this, it was only natural to have him playing his axe on the table to measure the success of the procedure.
Now, when I first heard of this, all I could think of was the possibility for comic dialogue:
"Mr. Adcock, sir, this is Dr. Bannerjee, can you hear me? Sir? Yes? Good good, very good. Now sir, we are ready to proceed and I want you to try something for me at this point. My assistant Dr. Kim has the probe in place, and what we want you to do ... [consults clipboard] ... is Foggy - Mountain - Breakdown. Did your hear me, sir? Good. Now ... begin.
Oh my goodness me, that is Turkey In The Straw. Remove the probe, Dr. Kim, we must try again ...."
Actually, as a lapsed member of the banjo community, I would not joke about this if Adcock wasn't doing very well. Here is the report from Adcock and his family, and here is some actual video from the surgery: