No one really knows what tomorrow will bring. The future is full of unknowns, and while this may stress a lot of us out, it’s a tremendous source of fear for people with two specific anxiety disorders.

Unlike most anxiety disorders, people with Obsessive Compulsive Disorder (OCD) and Generalized Anxiety Disorder (GAD) are particularly susceptible to stress over not knowing what’s going to happen down the road. Among these people, a quantifiable measurement called their Intolerance of Uncertainty has been linked to enlargement of a brain region called the striatum that’s responsible for decision making and motor control. But a paper published Thursday in Emotion found this same relationship in people who don’t have anxiety disorders: The higher the Intolerance of Uncertainty, the larger the striatum.

“There weren’t that many papers that reported on the effects of brain structure or anatomy,” says Justin M. Kim, one of the scientists at Dartmouth College who ran the study. Most of what we know about how the brain relates to anxiety disorders is related to function, not the brain’s actual structure.

Kim and his team ran fMRI scans on 61 undergraduates at Dartmouth College, none of whom had any psychological disorders. The researchers weren’t deliberately targeting the striatum, choosing instead to scan the entire brain for physical differences because so little is known about how neural anatomy is linked with anxiety. All of the participants completed surveys that measured their general feelings of anxiousness — people with anxiety disorders score well above a normal range — in order to separate them from Intolerance of Uncertainty measurements, which were also collected via survey. High Intolerance of Uncertainty scores are unique to OCD and GAD.

These findings, like many of those that come out of psychological studies, were limited by the tendency to collect data from undergraduates, especially since the striatum continues developing through people’s late twenties. Kim said that he didn’t find any difference within the age range that he studied, but his window into the minds of people who were just 18 to 26 years old is too narrow to generalize and say that age doesn’t impact the newfound relationship.

“If you collect brain data from a population that’s still developing, that might affect how you interpret your findings,” says Kim.

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putamen striatum fear anxiety gad ocd generalized disorder obsessive compulsive
Research shows that even in people without anxiety disorders, those with a larger putamen feel more anxious about an unpredictable future.

It’s too early to draw any clinical conclusions about how these findings could predict or help treat OCD and GAD, but this study could lay the groundwork for a new branch of experimentation into how brain anatomy affects psychology. Prior to this experiment, the link between striatum volume and anxiety over the future has only been looked at in people with anxiety disorders — no one had studied the normal variation in healthy people.

Kim hopes that his experiment will lay the foundation for using physical markers to track how well treatments for OCD and GAD are working or determining whether an enlarged striatum is a risk factor for developing an anxiety disorder. “Eventually, I hope this will help with a bigger wave of studies that might aid in the diagnosis of different psychiatric disorders using the brain,” he says.

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Abstract: Oversensitivity to uncertain future threat is usefully conceptualized as intolerance of uncertainty (IU). Neuroimaging studies of IU to date have largely focused on its relationship with brain function, but few studies have documented the association between IU and the quantitative properties of brain structure. Here, we examined potential gray and white-matter brain structural correlates of IU from 61 healthy participants. Voxel-based morphometric analysis highlighted a robust positive correlation between IU and striatal volume, particularly the putamen. Conversely, tract-based spatial statistical analysis showed no evidence for a relationship between IU and the structural integrity of white-matter fiber tracts. Current results converge upon findings from individuals with anxiety disorders such as obsessive– compulsive disorder (OCD) or generalized anxiety disorder (GAD), where abnormally increased IU and striatal volume are consistently reported. They also converge with neurobehavioral data implicating the putamen in predictive coding. Most notably, the relationship between IU and striatal volume is observed at a preclinical level, suggesting that the volumetric properties of the striatum reflect the processing of uncertainty per se as it relates to this dimensional personality characteristic. Such a relationship could then potentially contribute to the onset of OCD or GAD, rather than being unique to their pathophysiology.

Photos via Dartmouth College, Home Alone 1 / Hughes Entertainment