Poor sleep may be linked to declining memory in older people, research suggests.
Brain differences relating to sleep and memory were found by scientists who compared young and old volunteers.
Lack of slow-wave, or "deep" sleep, in older people was predictive of memory loss.
This in turn was associated with the age-related loss of neurons in the brain's medial prefrontal cortex (mPFC) region.
The research, published in the journal 'Nature Neuroscience', involved volunteers learning a set of words and repeating them after a night's sleep.
Dr Matthew Walker, from the University of California at Berkeley, US, and colleagues wrote in the journal: "These data support a model in which age-related mPFC atrophy diminishes SWA (slow-wave activity), the functional consequence of which is impaired long-term memory."
Commenting on the research, Dr Simon Ridley, from the charity Alzheimer's Research UK, said: "This small study makes a link between structural changes in the brain, sleep quality and memory in old age, but further investigation is needed to confirm the nature of this association."