Smallville :

To regain key incriminating information about his father's past that he lost when his memory was erased, Lex joins an experimental program headed by Dr. Garner.

Knowing that Lex will also remember the secret of Clark's powers if he regains his memory, Clark tries to stop him but Lionel and Garner capture Clark and expose him to the same radical treatment, hoping to reveal his mystery. Through the experiment, Clark learns about his birth mother.