At some point, most of us have experienced déjà vu: the brief, haunting sensation of repetition, in which an entirely new situation seems familiar. Although the feeling itself only lasts for a few seconds, the memory of it may linger for hours. The phenomenon is a sober reminder that the brain is not perfect, and that cognitive processes can misfire. But what exactly goes wrong?

According to Psychology Today, déjà vu is a notoriously difficult research subject, as it appears to be an exclusively sporadic phenomenon. Although 60-70% of the population has experienced it, déjà vu episodes are over in a matter of seconds, and there is no known way to induce one in a controlled setting. For this reason, a general theory is exceedingly difficult to formulate.

Neurologists and psychologists, however, are well-versed in such uncertain fields of inquiry. In a new TED Ed video, Michael Molina explains three of the most prominent theories put forward by researchers. While they may not provide the final answer, they all make a convincing case.