Almost a century ago, the origins of sleep science research began at the University of Chicago with the opening of the world's first sleep laboratory. Since then, sleep science has evolved into a multi-disciplinary field — with scientists focusing on diagnosing the causes of sleep disorders, to how sleep affects our metabolic health, and improving methods for good sleep hygiene. But at the core of sleep science, one fundamental question remains: Why do we sleep?

In our special series, The Day Tomorrow Began, we speak with two of the world's leading sleep researchers: Assoc. Prof. Esra Tasali, director of the UChicago Sleep Center; and Prof. Emmanuel Mignot, director of the Stanford Center for Narcolepsy.