Researchers at Har­vard Med­ical School and Mass­a­chu­setts Gen­er­al Hos­pi­tal have found that when you don’t get enough sleep, your brain can’t get rid of stress­ful mem­o­ries, lead­ing to anx­i­ety or post-trau­mat­ic stress dis­or­der (PTSD).

Sleep is known to be crit­i­cal to the con­sol­i­da­tion of our mem­o­ries, and sleep depri­va­tion impairs mem­o­ry and learn­ing. The study involved 150 healthy adults. They all had to spend a num­ber of nights in the sleep lab. A third of the par­tic­i­pants received nor­mal sleep, anoth­er third received restrict­ed sleep (the sub­jects slept only the first half of the night), and final­ly, a third did not sleep at all at night and suf­fered the most from lack of sleep the next morn­ing.

The fol­low­ing day, all project par­tic­i­pants under­went a fear con­di­tion­ing pro­ce­dure using a three-phase exper­i­men­tal mod­el to acquire and over­come fear­ful mem­o­ries. At the same time, the sub­jects’ brains were observed using func­tion­al MRI.

It turned out that activ­i­ty in the areas of the brain asso­ci­at­ed with the reg­u­la­tion of emo­tions (the pre­frontal cor­tex) is observed only in peo­ple who have had enough sleep. For those who slept half the night, activ­i­ty was great­est in areas of the brain asso­ci­at­ed with fear and least in areas of emo­tion con­trol.

But in peo­ple who did not sleep at all, activ­i­ty in areas of fear was quite low. And after 12 hours, their brain activ­i­ty was more like the brain of a sleepy per­son. This sug­gests that the lack of a night’s sleep for the psy­che is even worse than its com­plete absence. An analy­sis of the sleep of such peo­ple showed that sleep­ing for half the night leads to the loss of the rapid eye move­ment phase (REM phase) — this stage is impor­tant for mem­o­ry con­sol­i­da­tion.

Over­all, the find­ings explain why par­tial­ly sleep deprived peo­ple are par­tic­u­lar­ly vul­ner­a­ble to stress and prone to devel­op­ing anx­i­ety and PTSD.

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