An amazing study demonstrating this phenomenon was done by Marshall, Helgadottir, Molle and Born, at Germany's University of Lubeck in 2006. The researchers asked human subjects (13 lucky medical students) to remember the English translation of some German words right before going into sleep. During the first phase of slow-wave sleep, the experimenters induced slow-wave activity by applying oscillating currents (to the forehead) with the right frequency (0.75 Hz). The next morning, after the subjects woke up, they were asked to try to remember the words they had learned the previous day. The students who had the currents applied to their foreheads were able to remember more.

The authors went on to show that applying current during REM sleep phase did not improve memory performance. Also, applying the wrong frequency-for example, 5 Hz, which normally can be seen during REM sleep-didn't have the same effect.

Clearly this finding raises many questions about both theory as well as practice. Theoretically, this is one of the best examples showing that distinct brain oscillations do have sufficient effect on specific brain functions. Equally important, it provides new approaches to answer the question of how our brains consolidate memories. Practically, I can almost imagine that some people will start to apply currents to their heads right before a final exam or other important memory test! Maybe we will soon see some "MemoImprov" devices selling on eBay. I guess you need to make sure that you don't crank up the potential too much and fry your brain!

Ok, but why am I interested in this topic? One of my own research projects is looking at the synaptic learning rule, which is important for memory, in different oscillation states.