The study involved participants undertaking the boring task of pressing a button whenever numbers appeared on a screen. During the task their brain activity was measured using an fMRI scanner. The researchers followed participants' attention by using the scans, subjective reports from the participants and tracking their performance on the task.

Although it may seem that we are doing nothing when we are daydreaming, the study found that there was an increase in the activity of many brain areas. The brain areas that were active were those associated with complex problem solving.

"Mind wandering is typically associated with negative things like laziness or inattentiveness," claimed lead author, Prof. Kalina Christoff, UBC Dept. of Psychology. "But this study shows our brains are very active when we daydream – much more active than when we focus on routine tasks."

The researchers speculate that daydreaming may be an important cognitive state where we unconsciously disengage from what we are doing and sort through important problems in our lives.

Previously, it was thought that only brain areas involved in routine mental activity (the medial prefrontal cortex, the posterior cingulate cortex and the temporoparietal junction) were active during daydreaming; however, areas associated with high level, complex problem solving (the lateral prefrontal cortex and the dorsal anterior cingulate cortex) are also active.

"This is a surprising finding, that these two brain networks are activated in parallel," says Christoff. "Until now, scientists have thought they operated on an either-or basis – when one was activated, the other was thought to be dormant." The less subjects were aware that their mind was wandering, the more both networks were activated.

The quantity and quality of brain activity suggests that people struggling to solve complicated problems might be better off switching to a simpler task and letting their mind wander.

"When you daydream, you may not be achieving your immediate goal – say reading a book or paying attention in class – but your mind may be taking that time to address more important questions in your life, such as advancing your career or personal relationships," says Christoff.