says computational neuroscientist Nathan-
iel Daw of Princeton University, who was
not involved in the study. “This study sup-
ports the alternative idea that the compul-
sions themselves are a core deficit, not sec-
ondary to obsessions.”
De Martino is interested in the mecha-
nisms underlying decision-making in gen-
eral, and specifically the relationship be-
tween confidence and action. These are
normally so tightly tied together, it is diffi-
cult to study their relationship. But the
team saw that OCD might provide a natural
way of disentangling them. A standard view
is that confidence is calculated by monitor-
ing our actions; think about how much lon-
ger you take to act in uncertain situations.
“This is roughly the idea of monitoring
your own behavior to build confidence es-
timates, but this is not the only architec-
ture the brain could use,” De Martino says.
If confidence is estimated by monitoring
behavior, it should be impossible to sepa-
rate confidence from actions. But it is also
possible that confidence is calculated inde-
pendently (or “offline”) and can then be
used both for guiding action and reporting
confidence levels—a form of processing
known as a “parallel” architecture. The sec-
ond alternative “is exactly what our data
suggest,” De Martino says. “This is the gen-
eral appeal of this work beyond the specific
clinical interest; these patients can help us
distinguish between alternative cognitive
architectures.”
The results suggest the brain calculates
confidence independently of action, but
healthy functioning depends on linking
them tightly together. They are also con-
sistent with a “dual-systems” view of be-
havioral control that distinguishes be-
tween explicit, conscious reasoning and
more implicit, automatic behaviors, Daw
says. “A number of issues in psychiatry re-
lated to compulsion have to do with a dis-
connect, or imbalance, between these two
types of process.”
A major caveat is the study was a snap-
shot in time, of people who were already ill,
and so cannot settle questions of cause and
effect. “We donʼt know if this impairment
results from illness or caused it,” Daw says.
Figuring out how a general impairment like
this relates to patients’ specific obsessions
and compulsions will require studies of
people with OCD over long periods to see
how different aspects of the disorder evolve
over time. But if the uncoupling of actionsfrom beliefs is at the root of OCD, it rep-
resents a common disease mechanism that
potentially unites a wide range of patients
with quite different observable symptoms.
“The hope is that by understanding the
general mechanism, rather than focusing
on specific symptoms, we can guide new
therapies,” De Martino says. One implica-
tion of the current findings is that if com-
pulsive behavior is at the core of the disor-
der, treatments directly aimed at modify-
ing behavior (like cognitive behavioral
therapy) may be more effective than treat-
ments more tailored to obsessive, rumina-
tion-style thinking, Vaghi says.
The team next plans to investigate where
the mechanism behind this impairment is
located in the brain. Researchers already
know connections between parts of the
frontal cortex, which orchestrates higher
functions like planning and problem-solv-
ing, and deeper areas, including a region
called the ventral striatum, are abnormal in
OCD. Further, prediction errors, which are
what seemed to determine patientsʼ abnor-
mal actions, are primarily processed in the
ventral striatum. These findings suggest
circuits between the frontal and striatal ar-
eas may be the critical ones underlying this