Margen
Your brain runs on about 20 watts and burns roughly 20 % of the energy you spend in a day. Marcus Raichle, a neurologist at Washington University, published a map in 2001 of what your neurons do when you rest: they barely switch off. The drop in consumption between thinking hard and thinking nothing is around five per cent; the rest goes to the so-called default mode network —regions of the medial cortex that chew over memories and plan scenes while you think you're blank—.
Practical upshot: resting your head doesn't power it off, it changes the channel. When you're stuck on a concrete problem, two routines beat sitting at the screen.
Get up and walk fifteen minutes without headphones. The default network works well when the body bores itself and the eyes tire.
Write the problem down by hand, as you understand it today. Come back to it cold tomorrow morning with that note in front of you.