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A recent study conducted by scientists at UC Berkeley linked poor sleep habits and brain degeneration in the elderly with memory loss.
The study focused on how older adults between the ages of 60 and 80 store memory during slow-wave nonrapid eye movement sleep. During non-REM sleep, considered the deepest stage of sleep in which muscles are relaxed and no dreaming occurs, memory-firing sequences travel from the hippocampus to the prefrontal cortex and strengthen recent memories. In the elderly, however, disrupted sleep interferes with this firing sequence.
Bryce Mander, a postdoctoral fellow at UC Berkeley and first author on the paper published on Jan. 27, said the researchers began by questioning whether age-related changes in sleep patterns are connected with memory loss.
“We looked to see if sleep deficiency led to memory deficiency and found that the more their sleep was disturbed, the more their memory was disturbed,” Mander said. “As you age, we know that your ability to learn decreases and your ability to hold on to your memory decreases and that there is a link between the two.”
According to co-author Jared Saletin, a researcher in Berkeley’s psychology department, anatomical and physiological factors determine how the brain maintains memories.
“What we observed that was very interesting is that older adults have a structural difference in the prefrontal cortex and it is an area that changes in structure with age. That change in structure is related to changes in sleep-dependent memory,” Saletin said. “It shows that not only memory and sleep changes with age, but also underlying changes in brain structure change how we store memory.”
As people age and sleep grows more disrupted, the brain’s hippocampus, which processes short-term memory, experiences trouble transferring memories to the prefrontal cortex, which serves as an ‘external hard drive’ that stores long-term memories.
Assistant researcher in physiology at Berkeley and co-author of the paper Vikram Rao said that several inter related factors determine memory retention in older adults.
“There are four things going on here. The first thing is age, the second thing is grey matter atrophy, the third thing is sleep and the fourth thing is impaired long-term memory consolidation,” Rao said. “There is a neurological pathway where there is a deep atrophy in the prefrontal grey matter in relation to age. The medial prefrontal cortex mediates the flow of activity which is recombinant of sleep.”
Although age-related diseases can contribute to memory loss, the researchers examined the sleep habits of relatively healthy older adults to control for age-dependent afflictions that dampen memory. These adults were tested alongside healthy adults in their twenties. The results indicated that quality rather than length of sleep determines the extent of our memory storage.
“In consistency with previous suggestions is that after a night of sleep, older adults were worse off at remembering associations long-term compared to the young,” Rao said. “The reason their memory is impaired is due to a change in sleep. There is a disruption in older adults’ sleep that we believe leads to a disruption in their memory process.”
Mander hopes that through understanding how sleep affects memory retention, pharmaceutical remedies can encourage deep sleep and aid in enhancing and prolonging memory storage in the elderly.
“Since sleep is the issue, we can use treatments that target sleep disorders,” Mander said. “Then we can improve memory in older adults.”
A version of this article appeared on page 4 of February 5th, 2013’s print edition of the Nexus.