23 July 2008 From New Scientist Print Edition. Subscribe and get 4 free issues. Bob Holmes Enlarge imageTHE urge to pee too frequently might literally mess with your mind. Experiments in rats show that an overactive bladder changes brain activity. If the same is true in humans, it could in part explain the disrupted sleep, reduced ability to concentrate and confusion that often accompany ageing. "If you have an overactive bladder, you don't just have a bladder problem. It has neurobehavioural consequences," says Rita Valentino, a neuroscientist at the Children's Hospital of Philadelphia in Pennsylvania. As much as 17 per cent of the US population is affected by the disorder, which is characterised by uncontrolled bladder contractions, leading to frequent urination. It is often caused by a partial obstruction of the urethra, such as in men with enlarged prostates. Valentino and her colleagues mimicked this in rats by surgically constricting the outlet from the bladder. When the team scanned the rats' brains they found increased activation of a region of the brainstem called the locus coeruleus, which helps control alertness. In normal mammals, this region is activated only when the bladder is full, and helps the animal to disengage from other activities. In rats with overactive bladders, however, activation seems to occur continually. An overactive locus coeruleus triggered increased and disordered activity in the forebrain, which controls higher brain function (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0800969105). In people, this is likely to lead to anxiety, disrupted sleep and other behavioural problems. The study is the first to show that a bladder disorder can have a direct effect on brain function. "This helps complete the puzzle of why overactive bladder symptoms are so disruptive to quality of life," says Craig Comiter, a urologist at Stanford University School of Medicine in California. Bowel disorders such as irritable bowel syndrome may also overactivate the locus coeruleus, which would help explain the psychiatric disorders that often accompany IBS, Valentino says.