(Assuming that not only institutional ethics but my own sense of morality is not a constraint.)
A lot of the really interesting things we know about broad-scale human neurology, particularly some tricky stuff about the nature of consiousness, are due to the study of people who have suffered brain damage. If there were no ethical constraints, I would deliberately induce carefully controlled forms of brain damage on humans and observe the results.
(Assuming that not only institutional ethics but my own sense of morality is not a constraint.)
A lot of the really interesting things we know about broad-scale human neurology, particularly some tricky stuff about the nature of consiousness, are due to the study of people who have suffered brain damage. If there were no ethical constraints, I would deliberately induce carefully controlled forms of brain damage on humans and observe the results.