Study shows how sleep improves memory

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Study shows how sleep improves memory

29 Jun 2005 Medical News Today

A good night's sleep triggers changes in the brain that help to

improve memory, according to a new study led by researchers at Beth

Israel Deaconess Medical Center (BIDMC).

These findings, reported in the June 30, 2005, issue of the journal

Neuroscience and currently published on-line, might help to explain

why children - infants, in particular - require much more sleep than

adults, and also suggest a role for sleep in the rehabilitation of

stroke patients and other individuals who have suffered brain

injuries.

" Our previous studies demonstrated that a period of sleep could help

people improve their performance of 'memory tasks,' such as playing

piano scales, " explains the study's lead author , PhD,

director of BIDMC's Sleep and Neuroimaging Laboratory. " But we didn't

know exactly how or why this was happening.

" In this new research, by using functional magnetic resonance imaging

(fMRI), we can actually see which parts of the brain are active and

which are inactive while subjects are being tested, enabling us to

better understand the role of sleep to memory and learning. "

New memories are formed within the brain when a person engages with

information to be learned (for example, memorizing a list of words or

mastering a piano concerto). However, these memories are initially

quite vulnerable; in order to " stick " they must be solidified and

improved. This process of " memory consolidation " occurs when

connections between brain cells as well as between different brain

regions are strengthened, and for many years was believed to develop

merely as a passage of time. More recently, however, it has been

demonstrated that time spent asleep also plays a key role in

preserving memory.

In this new study, twelve healthy, college-aged individuals were

taught a sequence of skilled finger movements, similar to playing a

piano scale. After a 12- hour period of either wake or sleep,

respectively, the subjects were tested on their ability to recall

these finger movements while an MRI measured the activity of their

brain.

According to , who is also an Assistant Professor of Psychiatry

at Harvard Medical School, the MRI results showed that while some

areas of the brain were distinctly more active after a period of

sleep, other areas were noticeably less active. But together, the

changes brought about by sleep resulted in improvements in the

subjects' motor skill performance.

" The cerebellum, which functions as one of the brain's motor centers

controlling speed and accuracy, was clearly more active when the

subjects had had a night of sleep, " he explains. At the same time,

the MRIs showed reduced activity in the brain's limbic system, the

region that controls for emotions, such as stress and anxiety.

" The MRI scans are showing us that brain regions shift dramatically

during sleep, " says . " When you're asleep, it seems as though

you are shifting memory to more efficient storage regions within the

brain. Consequently, when you awaken, memory tasks can be performed

both more quickly and accurately and with less stress and anxiety. "

The end result is that procedural skills - for example, learning to

talk, to coordinate limbs, musicianship, sports, even using and

interpreting sensory and perceptual information from the surrounding

world -- become more automatic and require the use of fewer conscious

brain regions to be accomplished.

This new research may explain why children and teenagers need more

sleep than adults and, in particular, why infants sleep almost round

the clock.

" Sleep appears to play a key role in human development, " says

. " At 12 months of age, infants are in an almost constant state

of motor skill learning, coordinating their limbs and digits in a

variety of routines. They have an immense amount of new material to

consolidate and, consequently, this intensive period of learning may

demand a great deal of sleep. "

The new findings may also prove to be important to patients who have

suffered brain injuries, for example, stroke patients, who have to re-

learn language, limb control, etc.

" Perhaps sleep will prove to be another critical factor in a stroke

patient's rehabilitation, " he notes, adding that in the future he and

his colleagues plan to examine sleep disorders and memory disorders

to determine if there is a reciprocal relationship between the two.

" If you look at modern society, there has in recent years been a

considerable erosion of sleep time, " says . Describing this

trend as " sleep bulimia " he explains that busy individuals often

shortchange their sleep during the week - purging, if you will - only

to try to catch up by " binging " on sleep on the weekends.

" This is especially troubling considering it is happening not just

among adults, but also among teenagers and children, " he adds. " Our

research is demonstrating that sleep is critical for improving and

consolidating procedural skills and that you can't short-change your

brain of sleep and still learn effectively. "

Study co-authors include BIDMC researchers Gottfried Schlaug, MD,

PhD, Stickgold, PhD, Alsop, PhD and Nadine Gaab, PhD.

This study was supported by grants from the National Institutes of

Health and the Dana Foundation.

Beth Israel Deaconess Medical Center is a patient care, teaching and

research affiliate of Harvard Medical School, and ranks third in

National Institutes of Health funding among independent hospitals

nationwide. BIDMC is clinically affiliated with the Joslin Diabetes

Center and is a research partner of Dana-Farber/Harvard Cancer

Center. BIDMC is the official hospital of the Boston Red Sox. For

more information, visit bidmc.harvard.edu.

Beth Israel Deaconess Medical Center

bidmc.harvard.edu