From Nature:
Practice makes perfect when it comes to remembering things, but exactly how that works has long been a mystery. A study published in Science this week1 indicates that reactivating neural patterns over and over again may etch items into the memory.
People find it easier to recall things if material is presented repeatedly at well-spaced intervals rather than all at once. For example, you're more likely to remember a face that you've seen on multiple occasions over a few days than one that you've seen once in one long period. One reason that a face linked to many different contexts — such as school, work and home — is easier to recognize than one that is associated with just one setting, such as a party, could be that there are multiple ways to access the memory. This idea, called the encoding variability hypothesis, was proposed by psychologists about 40 years ago2.
More here.