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.