How does your brain control working memory?

When you use your working memory, you have instantly to retrieve many different memories and keep them all in your mind at once. For example, to talk to a friend on the phone, you need to recognise their voice, understand what they are saying, and think up replies. This 'on-line' information seems to be held in the prefrontal cortex area of your brain. Working memory is crucial for solving problems and making plans.