Sleep And Memory In The Aging Brain, Why They Forget

Sleep and memory in the aging brain is a fascinating area of research. One reason is that we know, just by observation, that forgetfulness is common in senior citizens. The question is why? Outside of Alzheimer’s disease and dementia, what mechanisms trigger normal forgetting in the aged?

New research findings reveal a connection between sleep, long term and short  memory, and also show why forgetfulness is more common in the elderly.

Sleep And Memory: Study Results

Human brains deteriorate with age. Sleep quality — specifically the slow-wave activity that occurs during deep sleep — also decreases as we get older. Previous research found that slow waves are generated in a brain region called the medial prefrontal cortex (mPFC). This area deteriorates as we age.

Neuroscientists from UC,Berkeley, asked whether age-related changes in sleep and brain structure are linked to impaired memory. They compared 18 healthy young adults (ages 18 to 25) to 15 healthy older adults (ages 61 to 81).

Before going to sleep, the subjects memorized and were tested on 120 word pairs. While they slept, their brain activity was measured using an electroencephalogram. After 8 hours of sleep, the subjects were tested on the same word pairs, this time while undergoing functional MRI (fMRI) scans to measure changes in brain activity. The study was funded by the National Institute on Aging (NIA).

Memory performance in older adults was significantly worse than in their younger counterparts. The seniors also had significantly less slow-wave activity. Brain structures differed between the age groups as well, with the most degeneration in the older group in the mPFC area. Interestingly, reduced mPFC volume was associated with lower slow-wave activity, regardless of age.

Follow-Up

To confirm that forgetting in older adults was sleep-dependent, the researchers asked participants to perform the same word-pair memory task after an 8-hour period of wakefulness. Seniors still performed worse on the memory tasks than the younger group. And, while sleep improved memory for the younger group, it did not help the seniors. Their memory was far worse compared to the younger group.

Of interest was the finding that seniors process memories through the hippocampus area, whereas young adults do so through the pre-frontal cortex.

Deep sleep helps the brain store and retain new facts and information. But as we age, sleep quality declines. This prevents memories from being saved by the brain at night.