London, Jan 17 (IANS): At work, while replying to an important email, you suddenly start planning your weekend or thinking about next holiday.

It takes a moment before you realise you were daydreaming.

It happened because your brain simply 'changed channels' and switched to autopilot mode.

To understand this sudden wandering of thoughts, researchers at the Max Planck Institute for Human Development in Berlin, Free University of Berlin and University Hospital Freiburg analysed 1.6 billion connections between 40,000 tiny areas of the brain in 19 participants aged between 21-31.

They found the highest agreement between structure and information flow in the 'default mode network' - which is responsible for inward-focused thinking such as daydreaming, imagination and self-referential thought.

“In comparison to other networks, the default mode network uses the most direct anatomical connections. We think that neuronal activity is automatically directed to level off at this network whenever there are no external influences on the brain,” said Andreas Horn, researcher at the centre for adaptive rationality at Max Planck Institute for Human Development in Berlin.

Living up to its name, the default mode network seems to become active in the absence of external influences.

In other words, the anatomical structure of the brain seems to have a built-in autopilot setting.

“Our findings suggest that brain automatically switches to something useful when it is not being used for other activities,” said Horn.

The brain only stays on autopilot until an external stimulus causes activity in another network like doorbell ringing, a colleague interrupting you or a loud bang in the distance, said the study.

The findings would contribute to better understand brain functioning in healthy people and other mental illenesses, it said.