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Electric Stimulation of Brain During Sleep Boosts Memory

Study suggests that early part of sleep cycle consolidates new memories

MONDAY, Nov. 6 (HealthDay News) -- The application of a weak electrical current to the brain during sleep can improve memory, according to a study published online Nov. 5 in Nature. The findings show that brain activity during stage 2 non-rapid eye movement (REM) sleep plays a key role in consolidating new memories.

Lisa Marshall, Ph.D., and colleagues at the University of Lubeck in Lubeck, Germany, conducted an experiment in which 13 healthy adults memorized 46 pairs of words. Electrodes were applied to frontolateral locations and at the mastoids before sleep. Four minutes after entry into non-REM sleep, the researchers induced a weak current for five intervals of five minutes each, with a one-minute break.

The experiment was conducted twice, once with stimulation and once with sham stimulation. In the control groups, subjects recalled 37.4 words before they went to sleep and 39.5 after they woke up. Subjects who received cortical stimulation recalled 36.5 words prior to sleep and 41.2 after waking, an 8 percent improvement in memory. Application of the current at different frequencies or points in the sleep cycle did not improve memory.

"Brain stimulation with oscillations at 5 Hz -- another frequency band that normally predominates during REM sleep -- decreased slow oscillations and left declarative memory unchanged," the authors note. "Our findings indicate that endogenous slow potential oscillations have a causal role in sleep-associated consolidation of memory."

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