 Encouraged by John M. Freeman, he refined the procedure in the 1980s and performed it many times.In 1987, Carson was the lead neurosurgeon of a 70-member surgical team that separated conjoined twins, Patrick and Benjamin Binder, who had been joined at the back of the head (craniopagus twins); the separation surgery held promise in part because the twin boys had separate brains.The Johns Hopkins surgical team rehearsed the surgery for weeks, practicing on two dolls secured together by Velcro.