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It’s no secret that our ability to remember things dulls as we get older. Now researchers have some clues about why that happens.

Scientists at the University of California, Berkeley, found a connection between disrupted sleep — common among the elderly — and memory loss. Their work suggests that as we age, we no longer experience the same deep sleep of our youth and in turn generates fewer of the slow brain waves that are critical for a sharp memory.

Slow waves are involved in transferring short-term memories from the hippocampus into long-term memories stored in the prefrontal cortex. According to the authors, normal adults spend a quarter of each night’s sleep in deep, non-rapid-eye-movement sleep, during which these slow waves are generated.

(MORE: Even Brief Exercise Can Improve Memory in Older Adults)

The study found that slow waves are created in the middle frontal lobe of the brain and the shrinkage of this region among older adults may be linked to their struggle to experience deep sleep. In older adults, this deteriorating sleep quality interferes with the ability to store memories properly overnight, causing some to be overwritten by new ones.

In the latest work, published in the journal Nature Neuroscience, the scientists compared sleep and memory skills among 18 healthy adults in their 20s and 15 healthy elderly adults, primarily in their 70s. All were asked to learn 120 tricky word pairings and were tested on their ability to recall them. The younger group scored about 25% better than the older group.

The participants then slept for eight hours while the researchers collected images of their dozing brains using electroencephalograms, or EEGs. Their memories were tested again after their slumber, this time while their brains were imaged using functional and structural Magnetic Resonance Imaging scans. These can detail which areas of the brain are active during specific tasks, and the researchers discovered that the second time around, the younger group scored better by about 55%.

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The scans also highlighted a strong link between the degree of middle-frontal-lobe-brain deterioration among the older participants and the quality of slow-wave activity during sleep. Participants in the elderly group experienced a deep-sleep quality that was 75% lower than the younger group on average.

The work doesn’t suggest that such biological changes responsible for sleep quality are the driving force behind memory issues that occur with age. Nor does it hint that the structural changes that occur in the brain with age can be reversed. But the researchers do hope that the results point to one of many factors behind senior moments, and that the understanding paves the way for new treatments. They are planning to test, for example, whether enhancing sleep in older adults could lead to improved overnight memory storage and ultimately better recall.

“Can you jump-start slow-wave sleep and help people remember their lives and memories better? It’s an exciting possibility,” said lead study author Bryce Mander, a postdoctoral fellow in psychology at UC Berkeley, in a statement. Boosting deep sleep, he says, can be relatively simple, and everything from increased physical activity to more invasive electric brain stimulation should be studied as potential ways to achieve deeper sleep.