Although we cannot predict if our brain signals us to stop taking that extra glass of champagne, our brains are hardwired to stop us from drinking more water than what is healthy. Scientists have found a "stop mechanism" that determines brain signals telling the individual to stop drinking water. The study provides a new insight into the human instincts that determine survival behaviour and are also of medical importance. "Different areas of the brain involved in emotional decision-making were activated when people drank water after becoming thirsty and when study participants followed instructions to keep drinking when no longer thirsty," said professor Derek Denton from University of Melbourne. The brain regions determining the signals to stop drinking have not previously been recognized in this context. The research identifies an important component in regulation and this "stop mechanism" that may prevent complications from excessive water intake, Denton added. Over drinking can reduce the salt concentration of the blood that can result in the swelling of the brain, a potentially fatal condition. Also known as polydipsia, it has been found in some patients with schizophrenia and in some marathon runners. The study used magnetic resonance imaging to scan two physiological conditions of the brain, starting with scanning brain regions during the experience of thirst. Participants were then removed from the scanner and asked to drink to satiation or "overdrink" and return for further scanning. According to Denton, the data are relevant to study the gratification of other instincts such as food intake, salt intake and sexual behaviour.