When you're really thirsty, there's nothing better than a tall glass of ice cold water. But when you're not thirsty at all, drinking water is sort of blah at best, and maybe even a little nauseating. Why is that?
According to researchers at the University of Melbourne, it's because drinking when you're thirsty activates a different part of the brain than drinking when you're not thirsty.
The researchers had 20 volunteers ride an exercise bike for one hour, then scanned their brains twice: first, as they drank to satisfy their thirst, and then again as they forced themselves to keep drinking when they were no longer thirsty.
The scientists found that drinking when thirsty activates the orbitofrontal cortex--an area of the brain linked to emotional decision making. Drinking when you're not thirsty, meanwhile, seems to activate brain regions that override an unconscious "switch" responsible for turning off thirst.
Drinking to Excess
So drinking when thirsty meets both a physical and emotional need, while forcing water down your gullet appears to trigger brain circuits that overrule an inherent safety mechanism that prevents us from drinking too much. Guzzle too much H2O and you can end up with low sodium levels, leading to excess fluid in the brain which can cause all sorts of problems.
So while occasionally drinking some water when you're not thirsty won't hurt you, the unpleasant sensation it provokes is there for a good reason.
"Feeling Thirsty? How Drinking Water Satisfies the Brain" (LiveScience)