When people were told to sit and do nothing, the PET scans showed a distinct surge of mental energy in some regions. The resting state turned out to be more active than the active state.
[…]
She called this mode the REST state, for Random Episodic Silent Thought. The surge of activity that the PET scans revealed was not a confound, Andreasen argued. It was a clue. In our resting states, we do not rest. Left to its own devices, the human brain resorts to one of its most emblematic tricks, maybe one that helped make us human in the first place.
It time-travels.
Source: The Human Brain Is a Time Traveler – The New York Times
Tim B.
https://en.wikipedia.org/wiki/Mental_time_travel