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Dreaming may take edge off bad memories

Nov. 24, 2011
Courtesy of the University of California - Berkeley
and World Science staff

They say time heals all wounds. Now, re­search has found that time spent dream­ing may al­so help.

Sci­en­tists from the Uni­vers­ity of Cal­i­for­nia, Berke­ley, found that dur­ing sleep’s dream phase, stress chem­is­try shuts down as the brain pro­cesses emo­tion­al ex­pe­ri­ences. As a re­sult the pain­ful edge is whit­tled off harsh mem­o­ries.

The find­ings of­fer clues to why we dream and why post-traumatic stress dis­or­der suf­fer­ers, such as war vet­er­ans, con­tin­ue to be haunt­ed by past pain­ful ex­pe­ri­ences and re­cur­ring night­mares, the sci­en­tists say.

“The dream stage of sleep, based on its un­ique neu­ro­chem­i­cal com­po­si­tion, pro­vides us with a form of over­night ther­a­py,” said Mat­thew Walk­er, a psy­chol­o­gist and neu­ro­sci­ent­ist at the uni­vers­ity and sen­ior au­thor of the study, pub­lished on­line Nov. 23 in the jour­nal Cur­rent Bi­ol­o­gy. He called the dream stage “a sooth­ing balm that re­moves the sharp edges from the pri­or day’s emo­tion­al ex­pe­ri­ences.”

In peo­ple with post-traumatic stress dis­or­der, the problem may be that “the emo­tion has not been prop­erly stripped away from the mem­o­ry dur­ing sleep,” he said. So when a “flash­back is trig­gered by, say, a car back­fir­ing, they re­live the whole vis­cer­al ex­pe­ri­ence once again.”

The re­sults, he said, of­fer some of the first in­sights in­to the emo­tion­al func­tion of Rap­id Eye Move­ment, or REM, sleep. That stage of sleep, where most dreams occur, typ­ic­ally takes up a fifth of a healthy hu­man’s sleep­ing hours. Pre­vi­ous brain stud­ies in­di­cate that sleep pat­terns are dis­rupted in peo­ple with mood dis­or­ders such as post-traumatic stress dis­or­der and de­pres­sion.

While hu­mans spend a third of their lives sleep­ing, there is no sci­en­tif­ic con­sen­sus on sleep’s func­tion. But the new re­search shows that “dur­ing REM sleep, mem­o­ries are be­ing re­ac­ti­vat­ed, put in per­spec­tive and con­nect­ed and in­te­grat­ed, but in a state where stress neu­ro­chem­icals are ben­e­fi­cially sup­pressed,” said Els van der Helm, a doc­tor­al stu­dent in psy­chol­o­gy at the school and lead au­thor of the stu­dy.

Thirty-five healthy young adults par­ti­ci­pated in it. They were di­vid­ed in­to two groups, each of whose mem­bers viewed 150 emo­tion­al im­ages, twice and 12 hours apart. Mean­while changes in their brain were tracked us­ing Mag­net­ic Res­o­nance Im­ag­ing, which em­ploys mag­net­ism and ra­di­o waves to scan struc­tures in the body. Half the par­ti­ci­pants viewed the im­ages in the morn­ing and again in the eve­ning, stay­ing awake be­tween the two view­ings. The oth­er half viewed the im­ages in the eve­ning and again the next morn­ing af­ter a full night of sleep.

Those who slept in be­tween view­ings re­ported a sig­nif­i­cant de­crease in their emo­tion­al re­ac­tion to the im­ages, the sci­en­tists said. The brain scans al­so showed a dra­mat­ic re­duc­tion in re­ac­ti­vity in the amyg­da­la, a part of the brain that pro­cesses emo­tions, al­low­ing the brain’s “ra­t­ion­al” pre­fron­tal cor­tex to re­gain con­trol of the par­ti­ci­pants’ emo­tion­al re­ac­tions, the re­search­ers said.

They al­so recorded par­ti­ci­pants’ elec­tri­cal brain ac­ti­vity while they slept, us­ing pro­ce­dures called elec­troen­cephalo­grams. They found that dur­ing dream sleep, cer­tain elec­tri­cal ac­ti­vity pat­terns de­creased, show­ing that re­duced lev­els of stress neu­ro­chem­icals in the brain soothed emo­tion­al re­ac­tions to the pre­vi­ous day’s ex­pe­ri­ences.

“We know that dur­ing REM sleep there is a sharp de­crease in lev­els of nor­ep­i­neph­rine, a brain chem­i­cal as­so­ci­at­ed with stress,” Walk­er said. “By re­pro­cess­ing pre­vi­ous emo­tion­al ex­pe­ri­ences in this neuro-chemic­ally safe en­vi­ron­ment of low nor­ep­i­neph­rine dur­ing REM sleep, we wake up the next day, and those ex­pe­ri­ences have been soft­ened in their emo­tion­al strength. We feel bet­ter about them, we feel we can cope.”

Walk­er said he was tipped off to REM sleep’s pos­si­ble ben­e­fi­cial ef­fects on post-traumatic pa­tients when a doc­tor at a U.S. De­part­ment of Vet­er­ans Af­fairs hos­pi­tal in the Se­at­tle ar­ea told him of a blood pres­sure drug that was in­ad­vert­ently pre­vent­ing re­cur­ring night­mares in the pa­tients. It turns out the ge­ner­ic drug had a side ef­fect of sup­press­ing nor­ep­i­neph­rine in the brain, there­by cre­at­ing a more stress-free brain dur­ing REM, re­duc­ing night­mares and pro­mot­ing bet­ter sleep, Walk­er said.

“This study can help ex­plain the mys­ter­ies of why these med­ica­t­ions help some PTSD pa­tients and their symp­toms as well as their sleep,” Walk­er said. “It may al­so un­lock new treat­ment av­enues re­gard­ing sleep and men­tal ill­ness.”


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They say time heals all wounds. Now, research has found that time spent dreaming may also help. Scientists from the University of California, Berkeley, found that during sleep’s dream phase, stress chemistry shuts down as the brain processes emotional experiences. As a result the painful edge is whittled off harsh memories. The findings offer clues to why we dream and why post-traumatic stress disorder sufferers, such as war veterans, continue to be haunted by past painful experiences and reccurring nightmares, the scientists say. “The dream stage of sleep, based on its unique neurochemical composition, provides us with a form of overnight therapy,” said Matthew Walker, a psychologist and neuroscientist at the school and senior author of the study to be published Nov. 23 in the journal Current Biology. He called the dream stage “a soothing balm that removes the sharp edges from the prior day’s emotional experiences.” Iin people with post-traumatic stress disorder, it may be “the emotion has not been properly stripped away from the memory during sleep,” he said. So when a “flashback is triggered by, say, a car backfiring, they relive the whole visceral experience once again.” The results, he said, offer some of the first insights into the emotional function of Rapid Eye Movement, or REM, sleep, which typically takes up a fifth a healthy human’s sleeping hours. Previous brain studies indicate that sleep patterns are disrupted in people with mood disorders such as why post-traumatic stress disorder and depression. While humans spend a third of their lives sleeping, there is no scientific consensus on sleep’s function. But the new research shows that “during REM sleep, memories are being reactivated, put in perspective and connected and integrated, but in a state where stress neurochemicals are beneficially suppressed,” said Els van der Helm, a doctoral student in psychology at UC Berkeley and lead author of the study. Thirty-five healthy young adults participated in it. They were divided into two groups, each of whose members viewed 150 emotional images, twice and 12 hours apart. Meanwhile changes in their brain were tracked using Magnetic Resonance Imaging, which employs magnetism and radio waves to scan structures in the body. Half the participants viewed the images in the morning and again in the evening, staying awake between the two viewings. The other half viewed the images in the evening and again the next morning after a full night of sleep. Those who slept in between viewings reported a significant decrease in their emotional reaction to the images, the scientists said. The brain scans also showed a dramatic reduction in reactivity in the amygdala, a part of the brain that processes emotions, allowing the brain’s “rational” prefrontal cortex to regain control of the participants’ emotional reactions, the researchers said. They also recorded participants’ electrical brain activity while they slept, using procedures called electroencephalograms. They found that during dream sleep, certain electrical activity patterns decreased, showing that reduced levels of stress neurochemicals in the brain soothed emotional reactions to the previous day’s experiences. “We know that during REM sleep there is a sharp decrease in levels of norepinephrine, a brain chemical associated with stress,” Walker said. “By reprocessing previous emotional experiences in this neuro-chemically safe environment of low norepinephrine during REM sleep, we wake up the next day, and those experiences have been softened in their emotional strength. We feel better about them, we feel we can cope.” Walker said he was tipped off to the possible beneficial effects of REM sleep on post-traumatic patients when a doctor at a U.S. Department of Veterans Affairs hospital in the Seattle area told him of a blood pressure drug that was inadvertently preventing reccurring nightmares in the patients. It turns out the generic drug had a side effect of suppressing norepinephrine in the brain, thereby creating a more stress-free brain during REM, reducing nightmares and promoting a better quality of sleep, Walker said. “This study can help explain the mysteries of why these medications help some PTSD patients and their symptoms as well as their sleep,” Walker said. “It may also unlock new treatment avenues regarding sleep and mental illness.”