The phrase "have on brain" means to constantly think about something, and its antonyms refer to the absence of such mental preoccupation. Antonyms include "forgetting," "neglecting," "ignoring," and "disregarding." When we forget something, we don't remember it easily or actively. When we neglect something, we don't give it enough attention, care, or importance. When we ignore something, we purposely dismiss it or fail to acknowledge its existence. When we disregard something, we consciously choose to not consider or follow it. Thus, using antonyms for "have on brain" can help us free ourselves from unwanted thoughts and focus on more productive endeavors.