For the longest while, researchers believed that you could only preserve a memory in your brain if the relevant neurons were active. However, it now looks like this isn't always the case -- and that could be a tremendous help to anyone suffering from short-term memory loss. Scientists have discovered that small jolts of electricity to the brain (specifically, a pulse of transcranial magnetic stimulation) can revive recent memories. Your mind can slow near-term memories down to a dormant state where they're in the background, but remain ready to come back when necessary.
You can't apply this method to long-term memories (you likely need different techniques for that), so don't expect to revisit your childhood with a zap to your head. However, the findings should improve our understanding of how the brain works -- it's already clear that memory is more complex than we thought. And in the long run, there's a chance this could lead to treatments for Alzheimer's and other conditions where regaining short-term memories could greatly improve a patient's quality of life.