Jonah Lehrer in the Boston Globe:
scientists have begun to see the act of daydreaming ... is a fundamental feature of the human mind - so fundamental, in fact, that it's often referred to as our "default" mode of thought. Many scientists argue that daydreaming is a crucial tool for creativity, a thought process that allows the brain to make new associations and connections. Instead of focusing on our immediate surroundings - such as the message of a church sermon - the daydreaming mind is free to engage in abstract thought and imaginative ramblings. As a result, we're able to imagine things that don't actually exist,
Every time we slip effortlessly into a daydream, a distinct pattern of brain areas is activated, which is known as the default network. Studies show that this network is most engaged when people are performing tasks that require little conscious attention, such as routine driving on the highway or reading a tedious text. Although such mental trances are often seen as a sign of lethargy - we are staring haplessly into space - the cortex is actually very active during this default state, as numerous brain regions interact. Instead of responding to the outside world, the brain starts to contemplate its internal landscape. This is when new and creative connections are made between seemingly unrelated ideas.
The article is here. Jonah Lehrer is an editor at large at Seed magazine and the author of "Proust Was a Neuroscientist."