Perseveration is the act of continuing to repeat something to an extreme degree. A person's perseveration might mean they keep asking you the same question over and over, despite the fact that you've answered them.
This word can describe a tendency to be repetitious or anxiously return to the same topic of conversation. It's also used in a more clinical way, for someone who has a disorder that causes them to be unable to switch off a specific thought or idea. Trauma to the brain can result in perseveration. The word shares a Latin root with persevere, which also means "continue," but has a more positive connotation than perseveration.