You walk out of the grocery store, ready to head home and make dinner. But as you scan the crowded parking lot, a frustrating question comes to mind. Where did you leave your car?
You try to picture the spot, but the memory refuses to surface. Remembering personal experiences like these depends on episodic memory, which allows us to recall events from our lives. These memories help form the foundation of long-term memory, whether they involve a childhood milestone, such as the first day of elementary school, or something that happened just minutes earlier, like parking your car.
This ability tends to weaken as we grow older. The sights, sounds, and other details associated with past experiences can become increasingly difficult to retrieve. Scientists still do not fully understand why this happens.
Although some memory decline is a common part of aging, the changes can become far more severe in people developing Alzheimer's disease. A new study from researchers at the University of California, Berkeley, offers important clues about what may be happening inside the aging brain. Neuroscientist Omer Sharon and his colleagues, working under the direction of former Berkeley sleep researcher Matthew Walker, discovered a connection between disrupted brain waves during deep sleep, declining memory performance, and the accumulation of tau, a protein associated with Alzheimer's disease.
The findings suggest that tau buildup in the brain's frontal cortex is linked to changes in the coordinated electrical activity that helps preserve memories overnight. "This is the first time we've shown this relationship between tau and how it messes with memory consolidation by attenuating traveling slow waves that originate in the frontal cortex," said Sharon, a postdoctoral researcher at UC Berkeley's Center for Human Sleep Science. The research was published in Nature Neuroscience.
How Deep Sleep Helps the Brain Store Memories Sleep involves several distinct stages, each associated with different patterns of brain activity. Rapid eye movement sleep is particularly recognizable because the eyes move beneath closed eyelids and most dreaming takes place during this stage. However, another stage, known as non-REM sleep, is especially important for maintaining healthy brain function.
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