Lead researcher Jan Born, a neuroscientist at the University of Lübeck in Germany, had 13 medical students learn a list of words, and then tested how many they remembered over time. He then had them repeat the exercise after a nap. Those who did not have electrical current passed through their brains while sleeping remembered an average of 37.42 words before sleep and 39.5 afterward, confirming that sleep is an important factor in learning. After administering the electrical current to the sleeping students, they remembered an average of 41.27 words upon waking, according to the results published in the journal Nature.
Born and colleagues theorize that the electrical current enhances a part of the sleep cycle associated with consolidating word memory -- an early part of the cycle called "slow wave sleep." During this cycle, the prefrontal neocortex -- the part of the brain linked to conscious thought an spatial reasoning -- shows regular electrical fluctuations. The electrical current in the study was adjusted to match these fluctuations.
When the current was applied at a different frequency or during a different part of the sleep cycle, no memory improvement was noted. The exact mechanism by which the electrical fluctuations improve memory consolidation remains unclear, the researchers said, but Born theorizes that the currents can cause brain cells to resonate. This then could strengthen the connections between the brain cells that are the physical representations of memories.
###