Mild sleep disturbance that induces shallow sleep, but does not reduce total sleep time, is sufficient to interfere with learning and memory, according to a report published online by Nature Neuroscience on January 18th.

People who sleep poorly often report memory problems, and previous research has shown that missing one night’s sleep reduces activation in an area of the brain called the hippocampus, which is involved in short-term learning, Dr. Ysbrand D. Van Der Werf, at the Netherlands Institute for Neuroscience, Amsterdam, told Reuters Health.

“We were interested to see whether we could nail that effect down to something more specific,” the researcher said. “The slow-waves (of non-rapid eye movement sleep) were our main candidate, since recent theories predict that they serve to bring the brain back into a state of high capacity - refresh the brain, so to speak.”

He noted that shallow sleep is caused by such factors as sleep apnea, obesity, stress, environmental noise, too much ambient light or an uncomfortable bed.

The research team used a mild, repetitive beeping sound to induce shallow sleep. Otherwise, sleep duration, efficiency, number of stage transitions and staging remained intact during the intervention.

The study included 13 healthy subjects, average age 60 years, whose memory was tested following a night of undisturbed sleep and again following a night of shallow sleep.

On the day before, the subjects viewed 50 images of houses and landscapes. During the test, subjects viewed 100 images and were asked to identify the original 50, while functional MRI scans were being recorded. Functional MRI is a type of MRI that detects the changes in red blood cells and capillaries as they deliver oxygen to “functioning” parts of the brain.

Memory scores were significantly lower following the night of shallow sleep, and functional MRI showed less blood flow in the front part of the right hippocampus.

“Deep sleep before learning allows for optimal hippocampal activity and benefits memory encoding,” they conclude.

There are simple rules for ensuring optimal sleep patterns, Dr. Van Der Werf said, such as “avoiding caffeine from the afternoon on, avoiding strenuous work or stress or worrying in the last few hours before sleep, exercise during the day, getting enough daylight, and making sure that the bedroom is for sleeping and not for watching television or working or angry telephone calls.”

“A less intuitive suggestion would be to reduce the time spent in bed to the time you actually need to sleep,” the investigator added. “Don’t lie in bed for 10 hours thinking that at least your body will get some rest, and end up sleeping only 7 of those 10 hours.”

“It is better to restrict your time in bed to 7 hours and make sure that time in bed equals time slept, rather than drifting in and out of sleep, because that causes sleep fragmentation.”

SOURCE: Nature Neuroscience 2009.