Scientists have known for decades that the ability to remember newly learned information declines with age, but it was not clear why. A new study may provide part of the answer.

The report, posted online on Sunday by the journal Nature Neuroscience, suggests that structural brain changes occurring naturally over time interfere with sleep quality, which in turn blunts the ability to store memories for the long term.

Previous research had found that the prefrontal cortex, the brain region behind the forehead, tends to lose volume with age, and that part of this region helps sustain quality sleep, which is critical to consolidating new memories. But the new experiment, led by researchers at the University of California, Berkeley, is the first to directly link structural changes with sleep-related memory problems.

The findings suggest that one way to slow memory decline in aging adults is to improve sleep, specifically the so-called slow-wave phase, which constitutes about a quarter of a normal night’s slumber.