During deep sleep, older people have less coordination between two brain waves that are important to saving new memories, a team reports in the journal Neuron.
To find out, Walker and a team of scientists had 20 young adults learn 120 pairs of words. “Then we put electrodes on their head and we had them sleep,” he says.
The electrodes let researchers monitor the electrical waves produced by the brain during deep sleep. They focused on the interaction between slow waves, which occur every second or so, and faster waves called sleep spindles, which occur more than 12 times a second.
The next morning the volunteers took a test to see how many word pairs they could still remember. And it turned out their performance was determined by how well their slow waves and spindles had synchronized during deep sleep.
Next, the team repeated the experiment with 32 people in their 60s and 70s. Their brain waves were less synchronized during deep sleep. They also remembered fewer word pairs the next morning.
And, just like with young people, performance on the memory test was determined by how well their brain waves kept the beat, says Randolph Helfrich, an author of the new study and a postdoctoral fellow at UC Berkeley.
The team also found a likely reason for the lack of coordination associated with aging: atrophy of an area of the brain involved in producing deep sleep. People with more atrophy had less rhythm in the brain, Walker says.
But the study also suggests that it’s possible to improve an impaired memory by re-synchronizing brain rhythms during sleep.
One way to do this would be by applying electrical or magnetic pulses through the scalp. “The idea is to boost those brain waves and bring them back together,” Helfrich says.
Walker already has plans to test this approach to synchronizing brain waves.