Simon Makin in Scientific American:
About 10 years ago David Adam scratched his finger on a barbed wire fence. The cut was shallow, but drew blood. As a science journalist and author of The Man Who Couldn't Stop: OCD and the True Story of a Life Lost in Thought, a book about his own struggles with obsessive-compulsive disorder, Adam had a good idea of what was in store. His OCD involved an obsessive fear of contracting HIV and produced a set of compulsive behaviors revolving around blood. In this instance he hurried home to get some tissue and returned to check there was not already any blood on the barbed-wire. “I looked and saw there was no blood on the tissue, looked underneath the fence, saw there was no blood, turned to walk away, and had to do it all again, and again and again,” he says. “You get stuck in this horrific cycle, where all the evidence you use to form judgments in everyday life tells you there’s no blood. And if anyone asked, you’d say ‘no.’ Yet, when you ask yourself, you say ‘maybe.’” Such compulsive behaviors, and the obsessions to which they are typically linked are what define OCD. Far from merely excessive tidiness, the mental disorder can have a devastating impact on a person’s life. Adam's story illustrates a curious feature of the condition. Sufferers are usually well aware their behavior is irrational but cannot stop themselves from doing whatever it is they feel compelled to do.
A new study published September 28 in Neuron uses mathematical modeling of decision-making during a simple game to provide insight into what might be going on. The game looked at a critical aspect of the way we perceive the world. Normally, a person's confidence about their knowledge of the surrounding environment guides their actions. “If I think it’s going to rain, I'm going to take an umbrella,” says lead author Matilde Vaghi. The study shows this link between belief and action is broken to some extent in people with OCD. As a consequence, what they do conflicts with what they know. This insight suggests compulsive behaviors are a core feature rather than merely a consequence of obsessions or a result of inaccurate beliefs.