Truly vegetating—thinking about absolutely nothing—is harder work than it seems. In fact, it can feel worse than focusing. A newly released research study helps clarify this mind-numbing phenomenon. Daniela Calvetti and a research team at Case Western University used a computer model to investigate the chemical effects of slowing down or completely clearing away one's thoughts. What they found is that "to stop a thought, the brain uses inhibitory neurons to prevent excitatory neurons from passing information from one to another." In effect, halting a thought is akin to "stopping a truck on a downhill slope." As any space cadet could tell you, it takes ample energy to clear your head as well as fill it.

"Maybe this explains why it is so tiring to relax and think about nothing," said Daniela Calvetti to the school's press team. The study itself, which was published in The Journal of Cerebral Blood Flow & Metabolism, got a more colorful rendering from The Daily Mail's David Derbyshire: "No matter how beautiful the beach or how stunning the slopes, millions of holidaymakers seem incapable of winding down while on vacation."

The problem would be solved, of course, if you didn't have any thoughts in the first place.