Most of us tend to accept that as we get older we will slowly become more and more forgetful. Separate from more serious dementia-related symptoms, this acceptance of a degree of age-induced memory loss is widespread. But why does this happen, and can it be stopped? A new study from UC Berkeley has uncovered a mechanism explaining age-related memory loss, and it all has to do with sleep.

It has long been understood that sleep plays a vital role in the process of consolidating memories from short-term storage to long-term, but how this plays out biologically has been unclear. The theory was that memories are saved during sleep when two types of brain waves fall into sync. The faster waves known as sleep spindles need to perfectly fall into line with deeper slower waves for memories to be properly consolidated.

"Timing is everything," says Randolph Helfrich, lead author of this new research. "Only when the slow waves and spindles come together in a very narrow opportunity time window (approximately one-tenth of a second), can the brain effectively place new memories into its long-term storage."

This new study reveals that when we age, our brain increasingly fails to accurately coordinate these two types of deep-sleep brainwaves and this results in an inability to accurately retain new memories. To verify this theory the researchers compared two groups of sleep subjects, 20 adults in their 20s and 32 adults in their 70s. The subjects were trained on a series of word sets before slumber and then their brainwaves were monitored while they slept.

The results were clear, with the older group consistently displaying an out-of-sync rhythm between their two key deep-sleep brainwaves. The following day, when both groups were tested on their memory of the word sets taught the previous day, their success or failure strongly correlated with how well their spindles and slow waves synced up overnight.

"The mistiming prevents older people from being able to effectively hit the save button on new memories, leading to overnight forgetting rather than remembering," says study senior author Matthew Walker.

All the subjects also underwent fMRI scans that revealed a degradation of the medial frontal cortex. This suggested to the researchers a potential source of the brain's inability to sync up these deep-sleep brainwaves. Walker says the results showed that the worse the deterioration was in this area of the brain, the more uncoordinated the deep-sleep brainwaves ultimately were.

The next step in the research is to examine whether targeted electrical brain stimulation could bring these brainwaves back into sync. Not only could this prove to be a way to help enhance the memory of senior citizens, but it could have a fundamental effect in improving our sleep as we age.

"By electrically boosting these nighttime brainwaves, we hope to restore some degree of healthy deep sleep in the elderly and those with dementia, and in doing so, salvage aspects of their learning and memory," says Walker.

The new research was published in the journal Neuron.

Source: UC Berkeley

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