You can find the answer in this link:

https://singularityhub.com/2025/03/20/new-baby-brain-scans-r...

They presumably don’t have any extra information except what’s in the article which said they “often squirmed” rather than always, which means simply repeating the process enough gives times when they didn’t.

If you want technique: “infants were _ to reduce movement.”

If you missed what was in the blank you might want to reread to see what else you missed.