Is it possible that the procedure itself, the act of drilling and poking needles into the brain, stimulated the improvement? The stem cells didn't linger and t

Is it possible that the procedure itself, the act of drilling and poking needles into the brain, stimulated the improvement? The stem cells didn't linger and they're precursors to skeletal muscular cells so maybe they actually had no effect on the outcome? Is it possible/ethical to do studies where they drill and poke into the brain without injecting stem cells?