To recap, sleep spindles are waves of brain activity during sleep as seen on an electroencephalogram (EEG). They begin appearing in sleep around the first six to eight weeks of life, after which they remain with the sleeper for life. These spindles are most evident during stage 2 sleep. Matthew Walker and his research team at the University of California Berkley found that sleep spindles are associated with the refreshment of the brain’s ability to learn. The greater the number of sleep spindles produced during sleep, the more that participants were refreshed to perform a learning task. Sleep spindles involve activation in the areas of the thalamus, anterior cingulate and insular cortices, and the superior temporal gyri. The brain areas most involved were the hippocampus and the prefrontal cortex—both of these areas are critical for learning.Furthermore, some very important brain activities are carried out when sleep spindles are occurring, whether during nighttime sleep or daytime naps. Herein lies the rub for many people, especially if their circadian rhythm is altered.