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Loss of deep sleep affects memory

29th January 2013

Researchers in California say a decrease in the amount of deep sleep a person gets as they age could affect their ability to remember new information.

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Certain regions of the brain needed to remember new information get smaller with age, and this could be linked to a drop in the amount of time spent in deep, or slow-wave, sleep.

Scientists at the University of California at Berkeley say structural changes in the ageing brain could be linked to memory loss in older people.

A region of the brain known as the prefrontal cortex, just behind the forehead, loses volume as people get older.

It is instrumental in sustaining the kind of deep sleep needed for new memories to be stored.

Writing in the journal Nature Neuroscience, the researchers report their the new experiment is the first to make a direct link between structural changes and sleep-related memory problems.

Normally, around a quarter of a normal night's sleep is spent in slow-wave sleep.

The California study looked at brain images from 18 people in their early 20s and 19 retired people, noting that the prefrontal cortex was on average a third smaller in the older age group than in the younger people.

Previous research suggests that natural atrophy is the main factor behind this shrinkage.

The groups were then put through verbal memory tests before bed that asked them to remember pairs of words, one of which was nonsense, and the other of which was a recognisable English word.

The nonwords were important because the memory function being tested is for the storage of new information not previously encountered.

The younger group's scores when asked to recall the pairs following a half-hour learning session was around 25% higher on average than the older group's scores.

Then both groups went to sleep, and were monitored for high-quality slow-wave sleep. The older group only spent a quarter of the time that the younger group enjoyed in this sort of sleep.

Previous research has suggested that the brain uses the slow-wave patterns to move memories from temporary to long-term storage.

A second test was given the following morning, and the younger group performed around 55% better than the older group.

The difference between the evening and morning scores in each individual was also linked to the amount of atrophy in their prefontal cortex.

According to study lead author Bruce A. Mander, an analysis of the brain images showed that the differences in scores were not the result of changes in the person's capacity for memory, but to differences in the quality of their sleep.

However, study co-author Matthew P. Walker said that medial prefontal atrophy was probably not the only factor in age-related memory problems.

Some researcher have been experimenting with electrical stimulation to help older people enjoy longer periods of deep sleep.

Electrodes placed on the scalp transmit a low-level current across the prefontal cortex and stimulate the slow-wave pattern that is so beneficial to memory storage.

However, there is no way to reverse structural changes that occur with age.

Some studies have shown that people treated in this way had improved memories. However, experts say there are other ways to improve the quality of sleep, such as getting plenty of exercise.

According to psychology professor Ken Paller of Northwestern University, other structural brain changes also have an impact on memory as a person ages.



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