A change in brainwave coordination during sleep may at least partially explain how memories begin to fade among older people, even those who are otherwise healthy and show no signs of dementia.
“Memory consolidation” takes place while we’re asleep. Information we have learned over the previous day that is worth retrieving is transferred from short- to long-term memory. The process engages two types of brainwaves — slow and so-called “spindles” — that must sync up for the transfer to work.
For older adults, the study found, the coordination of the brainwaves is not as finely tuned as in younger adults. In the study, 20 healthy adults in their 20s and 32 healthy older adults typically in their mid-70s were tested. After learning 120-word sets, participants slept for a full night. When tested on the word pairs the following morning, electroencephalography results showed that the spindles “missed syncing up with the slow waves.”
"Timing is everything. 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," study lead author Randolph Helfrich, a postdoctoral fellow in neuroscience at the University of California at Berkeley, told "Science Daily."
“Like swinging a tennis racket during a ball toss to serve an ace,” according to a release about the study, “slow and speedy brainwaves during deep sleep must sync up at exactly the right moment to hit the save button on new memories.”