Drinking a glass of cold water when you feel thirsty on a muggy summer evening is pleasant but if you go on drinking a few more glasses, the experience turns unpleasant. Researchers have now discovered why.
Two areas of the brain - anterior cingulate cortex and the orbitofrontal cortex - that are involved in emotional decision-making lit up when people drank water when they were thirsty.
Whereas the regions involved in controlling movement - putamen, cerebellum and motor cortex - kick in when they continued drinking even after quenching thirst, the study found.
To find out the root of these experiences, researchers scanned the brains of 20 healthy men and women as they drank cold water.
The post-drinking scans also showed activity in the midcingulate cortex, insula, amygdala and periaqueductal gray - areas involved in emotion, motivation and more basic brain functions.
Drinking too much water can also lead to dangerously low sodium levels.
The study appeared in the journal Proceedings of the National Academy of Sciences.