To lobotomize is to perform a lobotomy on someone, which is defined as to make an incision in the front lobe of the brain to deprive the person of independent thought.(verb)
When you perform surgery and make an incision in the front part of someone's brain, this is an example of a situation where you lobotomize.
See lobotomize in Webster's New World College Dictionary
See lobotomize in American Heritage Dictionary 4
transitive verb lo·bot·o·mized, lo·bot·o·miz·ing, lo·bot·o·miz·es