Sleep Selectively Preserves Emotional Memories

As poets, songwriters and authors have described, our memories range from misty water-colored recollections to vividly detailed images of the times of our lives.

Now, a study led by researchers at Beth Israel Deaconess Medical Center (BIDMC) and Boston College offers new insights into the specific components of emotional memories, suggesting that sleep plays a key role in determining what we remember – and what we forget.

Reported in the August 2008 issue of the journal Psychological Science, the findings show that a period of slumber helps the brain to selectively preserve and enhance those aspects of a memory that are of greatest emotional resonance, while at the same time diminishing the memory’s neutral background details.

“This tells us that sleep’s role in emotional memory preservation is more than just mechanistic,” says the study’s first author Jessica Payne, PhD, a Harvard University research fellow in the Division of Psychiatry at BIDMC. “In order to preserve what it deems most important, the brain makes a tradeoff, strengthening the memory’s emotional core and obscuring its neutral background.”

Previous studies have established the key role that sleep plays in procedural memory, demonstrating that the consolidation of procedural skills (such as typing or playing the piano) is greatly enhanced following a period of sleep.

But sleep’s importance in the development of episodic memories – in particular, those with emotional resonance– has been less clear.

“Emotional memories usually contain highly charged elements – for example, the car that sideswiped us on the ride home – along with other elements that are only tangentially related to the emotion, such as the name of the street we were traveling on or what store we’d just passed,” explains study author Elizabeth Kensinger, PhD, an Assistant Professor in the College of Arts and Sciences at Boston College. “We were interested in examining whether sleep would affect memory for all of these elements equally, or whether sleep might allow some of the event features to decay at a faster rate than others.”

The authors tested 88 college students. Study participants were shown scenes that depicted either neutral subjects on a neutral background (a car parked on a street in front of shops) or negatively arousing subjects on a neutral background (a badly crashed car parked on a similar street). The participants were then tested separately on their memories of both the central objects in the pictures and the backgrounds in the scenes. In this way, memory could be compared for the emotional aspects of a scene (the crashed car) versus the non-emotional aspects of the scene (the street on which the car had crashed.)

Subjects were divided into three groups. The first group underwent memory testing after 12 hours spent awake during the daytime; the second group was tested after 12 nighttime hours, including their normal period of nighttime sleep; and the third baseline group was tested 30 minutes after viewing the images, in either the morning or evening.

“Our results revealed that the study subjects who stayed awake all day largely forgot the entire negative scene [they had seen], with their memories of both the central objects and the backgrounds decaying at similar rates,” says Payne. But, she adds, among the individuals who were tested after a period of sleep, memory recall for the central negative objects (i.e. the smashed car) was preserved in detail.

“After an evening of sleep, the subjects remembered the emotional items [smashed car] as accurately as the subjects whose memories had been tested only 30 minutes after looking at the scenes,” explains Kensinger. “By contrast, sleep did little to preserve memory for the backgrounds [i.e. street scenes] and so memory for those elements reached a comparably low level after a night of sleep as it did after a day spent awake.”

“This is consistent with the possibility that the individual components of emotional scene memory become ‘unbound’ during sleep,” adds Payne, explaining that “unbinding” enables the sleeping brain to selectively preserve only that information which it calculates to be most salient and worthy of remembering. A real-world example of this tradeoff, she adds, is the “weapon focus effect” in which crime victims vividly remember an assailant’s weapon, but have little memory for other important aspects of the crime scene. Traumatic memories, such as the flashbacks experienced among individuals with post-traumatic stress disorder, can demonstrate similar disparities, with some aspects of an experience seemingly engraved in memory while other details are erased.

“Sleep is a smart, sophisticated process,” adds Payne. “You might say that sleep is actually working at night to decide what memories to hold on to and what to let go of.”

This study was supported, in part, by grants from the National Science Foundation and the National Institute of Mental Health. Coauthors include Elizabeth Kensinger, PhD, of Boston College, Robert Stickgold, PhD, of Beth Israel Deaconess Medical Center; and Kelley Swanberg of Harvard University.

Beth Israel Deaconess Medical Center is a patient care, teaching and research affiliate of Harvard Medical School, and consistently ranks among the top four 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 www.bidmc.harvard.edu.

Proper Mattress Can Improve Sleep Comfort, Reduce Pain

ARLINGTON, Va., Oct. 9 (medianowonline)- A good night's sleep is an essential part of a healthy lifestyle; however, an estimated 70 million Americans complain of sleeplessness. This October, during National Chiropractic Month, the American Chiropractic Association (ACA) is offering advice to help consumers select comfortable mattresses and pillows that can help limit unnecessary back and neck pain.


"Americans spend one-third of their lives sleeping, so it makes sense to invest in a sleep set that can improve your comfort and overall health," says Scott Bautch, DC, DACBOH, spokesperson for the American Chiropractic Association. "Many people don't realize the reason for their neck or back pain is literally right underneath them -- it's their mattress and pillow."


A 2006 study published in the Journal of Chiropractic Medicine showed that sleeping on a new mattress can significantly reduce stiffness and back pain. Researchers found that study participants reported immediate and sustained benefits after sleeping on a new mattress. This was especially true of participants who entered the study with back pain complaints, as they reported a 63 percent improvement in back discomfort with a new mattress.


When it comes time to purchase a new mattress, the ACA recommends the following:


Shop for Support


Look for a mattress that provides uniform support from head to toe; if there are gaps between your body and the mattress (such as at the waist), you're not getting the full support you need. Mattresses can be too firm; pay close attention to uncomfortable pressure on prominent body features such as the shoulders, hips and low back.


Shop for Comfort


When mattress shopping, give each option a good trial run before you buy; lie down on a mattress for a minimum of five to 10 minutes to get a good idea of its comfort level. If you cannot find a comfortable position, you probably have the wrong mattress.


Shop for Size


Does the bed provide enough room for both you -- and your sleeping partner if you have one -- to stretch and roll over? The ideal mattress will also minimize the transfer of movement from one sleeping partner to the other, which means one person shouldn't feel motion as the other leaves the bed.


Generally, a mattress should be replaced every 5 to 8 years to ensure proper support and comfort. Be aware that life's changes can signal the need for a new mattress as well. For example, people who have lost or gained a considerable amount of weight, those who have a medical condition which has changed the way they sleep, or even those who've changed partners may need to consider a new mattress.


Pillows important, too


After investing in a quality mattress, don't forget to choose an equally supportive pillow, advises ACA spokesperson Steven Conway, DC, DACBOH, Esq. "People will spend thousands of dollars on a mattress and then skimp on a pillow that doesn't support their head and neck properly," he observes.


When selecting a new pillow, ACA recommends selecting one with ergonomically-designed features, which will enhance comfort and limit pain. Look for pillows that are:


-- Designed to keep the spine in natural alignment. When lying on your side, your head and neck should remain level with your mid and lower spine. When lying on your back, your head and neck should remain level with your upper back and spine. Avoid pillows that are so thick or thin that they angle your head and neck away from your body.


-- Designed to support different sleep positions, including side sleeper or back sleeper. (It's best never to sleep on your stomach, as it's the most back unfriendly sleeping position.)


-- Hypoallergenic.


There is no such thing as a universal fit when it comes to pillows, Dr. Conway notes. "Find a pillow that is consistent with the shape and size of your body. If you find yourself sleeping on your side with one hand propped under your pillow, that's a clue that you're not getting the support you need from that pillow," he explains.


If you continue to experience pain and discomfort at night or have difficulty falling asleep, visit your doctor of chiropractic. Doctors of chiropractic are trained to treat spinal problems that can interfere with a restful night's sleep. They can also offer nutritional and ergonomic advice that can help improve the quality of your sleep. To find a chiropractor near you, view ACA's searchable member database at www.ACAtoday.org/DOCsearch.