Fragmented sleep is linked to memory impairment in mice, according to a new study by Stanford sleep researchers. The paper, published in the Proceedings of the National Academy of Sciences, is the first to isolate the effects of interrupted sleep on memory and was inspired in part by another study linking shorter sleep to hyperactive children.

The researchers behind the study stimulated “mini-awakenings” in mice by injecting a virus containing a red fluorescent protein, targeting brain cells in the hypothalamus that are involved in waking. They then used a laser that the proteins were responsive to in order to stimulate that area of the brain and briefly awaken the mouse’s brain. The procedure did not disrupt the amount of restorative sleep the mice experienced.

Before the mice slept, the researchers introduced them to two new areas of a cage; after the night of mini-awakenings, the mice were reintroduced to one of those areas and a newer area. If the mice remembered the familiar area, they would spend more time exploring the new area. All the sleepy mice, however, explored the two areas as if both were new, suggesting that they had forgotten the familiar space.

While interrupted sleep has long been linked to poor memory, researchers were previously unclear as to what other problems associated with interrupted sleep — poor overall sleep quality, interference with some specific part of the sleep cycle or annoyance from constantly being woken up — might be the actual issue.

A wide range of human disorders can similarly interrupt sleep, including Alzheimer’s disease, alcoholism and sleep apnea, and have long been associated with memory problems. That poor memory then negatively affects learning ability, as new skills and information are not as strongly retained.

— Ivy Nguyen