Poor sleep may be linked to declining memory in older people, research has revealed.
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 asking volunteers to learn a set of words and repeat them after a night's sleep.
Dr Matthew Walker, from the University of California at Berkeley, US, and colleagues wrote: "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.
"Such findings suggest that sleep disruption in the elderly, mediated by structural brain changes, represents a contributing factor to age-related cognitive decline in later life."
Dr Simon Ridley, of Alzheimer's Research UK, said: "This small study makes a link between structural changes in the brain, sleep quality and memory in old age. Increasing evidence has linked changes in sleep to memory problems and dementia, but it's not clear whether these changes might be a cause or consequence.
"The people in this study did not have dementia, but understanding the different factors that influence our brain health as we age could be crucial in the fight against the condition."