NASA agents burst into a Denny’s in Southern California five months ago to arrest a 74-year-old grandmother who was trying to sell a moon rock to raise money for her son’s medical expenses, according to a recent AP report. The elderly woman told a reporter that she was so terrified during the sting that she lost control of her bladder. Why do people become incontinent when frightened?
Blame the limbic system. Bladder control requires a sophisticated interplay of brain regions. An area of the brainstem known as the pontine micturition center is in constant contact with the bladder. It knows when pressure is building, and makes the preliminary decision to void. Thankfully, this area doesn’t have exclusive control over our bathroom habits, or we’d urinate whenever (and wherever) our bladders become full. The prefrontal cortex can override the desire to pee by sending an inhibitory signal to the brainstem. Under stressful conditions, however, the inhibitory signals from the frontal lobe can themselves be overridden by the limbic system, a combination of brain areas that controls the famous “fight or flight” response. When we become stressed or anxious, electrical signals from the limbic system become so intense that the brainstem has trouble following the frontal lobe’s commands. That’s why many people urinate more frequently before important exams or in the starting corral of a marathon. In life-threatening situations, the limbic system’s orders become so urgent that you can’t even make it to the bathroom.
That’s the neurobiological explanation, at least. The larger evolutionary question—of why incontinence might be advantageous in a survival situation—has no satisfying answer. What’s clear is that urinating in the face of danger pervades the animal kingdom. Gazelles wet themselves with a lion in hot pursuit. Pigeons often become incontinent when chased by wild-eyed toddlers. Laboratory rats have a nasty habit of peeing all over researchers’ hands. Some speculate that the instinct is related to the practice of marking territory with urine to prevent conflict. Alternatively, it may be that urinating could put a pursuing predator off the trail. In the absence of a good explanation, you’re free to speculate.
There’s a related condition known as paruresis, or shy bladder. Sufferers find it nearly impossible to urinate in the presence of others. The neurological basis for the disorder is very poorly understood, but it seems to be the neurological opposite of what happened to the target of NASA sting. The inhibitory signal from the prefrontal cortex becomes hyperactive, for some reason. You might think of paruresis as the story of civilization run slightly amok. The brainstem acts on a primordial level, controlling our most basic behaviors. The prefrontal cortex evolved inhibitory centers to control impulses. Without it, we would urinate and defecate freely, and violate all manner of social norms. The importance of these inhibitory centers can be seen in patients with Alzheimer’s, stroke victims, and those who have suffered catastrophic brain injuries. Oftentimes, they lose control over their excretory habits.
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Explainer thanks David Diamond of the University of South Florida, Gary Fisk of Georgia Southwestern University, Roy Freeman of Harvard Medical School, and Gert Holstege of the University of Groningen.