A

bout 10 years ago David
Adam scratched his finger
on a barbed wire fence. The
cut was shallow, but drew
blood. As a science journal-
ist and author of The Man Who Couldnʼt
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 con-
tracting HIV and produced a set of compul-
sive 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 thereʼs no blood. And if anyone asked,

youʼd say ‘no.’ Yet, when you ask yourself,

you say ‘maybe.’”

Such compulsive behaviors, and the ob-

sessions to which they are typically linked,

are what define OCD. Far from merely ex-

cessive tidiness, the mental disorder can

have a devastating impact on a person’s

life. Adamʼs story illustrates a curious fea-

ture of the condition. Sufferers are usually

well aware their behavior is irrational but

cannot stop themselves from doing what-

ever it is they feel compelled to do.

A new study published September 28 in

Neuron uses mathematical modeling of de-

cision-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

personʼs confidence about their knowledge

of the surrounding environment guides

their actions. “If I think it’s going to rain,

Iʼm 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 con-

sequence, what they do conflicts with what

they know. This insight suggests compul-

sive behaviors are a core feature rather than

merely a consequence of obsessions or a

result of inaccurate beliefs.

The research of Vaghi and colleagues

demonstrates the type of research being

performed by the relatively new field of

computational psychiatry. The work could

ultimately lead to tools for early detection

of people at risk. The field also may help

pave the way for improved diagnosis based

on understanding the biological or cogni-

tive mechanisms of mental disorders rath-

er than merely observing symptoms, as

psychiatrists currently do. A more mecha-

nistic analysis might also reveal that a ten-

dency to repeat inappropriate actions (a

compulsivity “trait”) is shared among mul-

tiple disorders such as OCD, substance

abuse and eating disorders. And this type

of analysis might distinguish among differ-

ent types of OCDs and give psychiatrists a

better idea about who might respond best

to particular treatments.

In principle, the fact that beliefs and ac-

tions in OCD patients are often at odds

could have several explanations. It is possi-

ble their ability to learn about the environ-

Simon J. Makin is an auditory perception researcher turned
science writer and journalist. Originally from Liverpool in the
north of England, he has a bachelor's in engineering, a master's
in speech and hearing sciences, and a Ph.D. in computational
auditory modeling from the University of Sheffield. He spent
several years working as a research fellow in the psychology
department at the University of Reading before recently branch-
ing out and retraining in journalism.