|A study led by neuroscientists at the University of California, Berkeley has linked the decline in the amount of good-quality sleep people get as they age with a reduction in their ability to remember things. (stylephotographs/123rf)|
The study, led by neuroscientists at the University of California, Berkeley, examined the relationship between memory retention, age and the quality of an individual’s slow wave non-rapid eye movement sleep.
“We wanted to understand whether sleep was a chief factor in memory loss,” explained Bryce Mander, the lead author of the study and a postdoctoral fellow at the university.
The scientists tested the short-term memory of two groups ― the first in their early twenties and the second of retirement age. The sleep wave activity of both groups was measured on an electroencephalogram machine, or EEG. The study found that, consistent with previous research, younger adults spend much longer in high quality NREM sleep.
However, Mander does not believe that age directly determines the quality of an individual’s sleep. Instead, the study suggests a direct correlation between quality slow wave sleep and the size of the brain’s hippocampus ― one of a group of brain structures surrounding the brain stem.
Because the hippocampus decreases in size with age, the amount and quality of slow wave sleep also decreases.
The hippocampus is responsible for the brain’s ability to store and retrieve episodic memories.
“If you remember where you were for breakfast this morning ― what you ate, whether you liked it or not ― that type of memory is episodic memory, and this type of memory depends on the hippocampus,” Mander explained.
A healthy young adult spends about 2 hours in slow wave sleep, but the retirement-age adults tested in this research project received less than half that amount.
“The older adults spent about 20 to 50 minutes in deep sleep,” Mander said. “It’s a massive difference ― and the electrical quality is about 75 percent lower.”
After sleeping, the episodic memory of the subjects was tested ― using lists of paired words memorized the night before. The younger test group scored 55 percent higher than the older group, despite only outperforming them by 25 percent the night before. The amount of slow wave sleep each individual received directly correlated with their test scores.
The researchers hope that these results will pave the way for future memory loss preventions, based around improving slow wave NREM sleep.
While atrophy of the hippocampus is a natural process of aging, there are some scientifically recognized ways of improving deep, slow-wave sleep ― some more practical than others.
“It’s been shown that if you exercise in the morning or the afternoon, your deep sleep is better,” Mander said. “There is another method which is putting electrodes on their head to mimic long waves and that improves your deep sleep rhythms.”
And it is never too early to start working on improving sleep rhythms.
The older group in this study ranged between 62 and 81-years-old, but this age group is not the only one affected.
“We were looking at people in their retirement age. However, sleep disruption starts much earlier than that,” Mander said. “Deep sleep disruptions start in your early 30s.”
However, Mander cautioned against overestimating the importance of sleep in preventing memory loss.
“I don’t think that we’ve found the answer,” he said. “But we’ve found an answer ― we’ve highlighted that sleep is one factor.”
By Lara Pearce (firstname.lastname@example.org)