Researchers from the University of Kent in the United Kingdom have identified a number of new ways that aging may impact one’s ability to obtain a good night’s sleep, according to Bustle.

The report, published in the journal Neurobiology of Aging, details a discovery that suggests with age, a certain structure in the brain appears to grow less sensitive to light. This structure, known as the suprachiasmatic nucleus (SCN), controls an individual’s circadian rhythm.

While you may have heard the term “circadian rhythm” in passing before, it is important to understand just how important of a role it plays in one’s sleep habits before you are to grasp the weight of this new finding. According to the National Sleep Foundation, a circadian rhythm is not a concrete structure in the brain, rather it is “basically a 24-hour internal clock that is running in the background of your brain and cycles between sleepiness and alertness at regular intervals.” The circadian rhythm is why you probably begin to fade after too many hours awake, and why you may experience a midday slump.