It is the movement of potassium (and also sodium) ions that causes the electrical impulses that nerve cells carry including the impulses found in slow-wave sleep.

ECONOMIST: Memory formation

First the team showed that they could use the state of a region of the brain, called the medial prefronal cortex, to predict how much deep, or slow-wave, sleep a person would have.

BBC: Boosting sleep 'may slow memory rot'

In earlier experiments, designed to replicate normal learning, Dr Tononi found that the part of the brain showing most slow-wave activity during sleep was the same as the part that had been activated during the experiment.

ECONOMIST: Memory formation

But some epilepsy medicines, including Neurontin from Pfizer and Gabitril from Cephalon (nasdaq: CEPH - news - people ), may also help slow wave sleep.

FORBES: Sleep On Demand