People who struggle with the ambiguity of the future tend to have a larger striatum, according to new neuroimaging research published in the journal Emotion.

The study found people who had difficulty tolerating an uncertain future had a greater volume of gray matter within the striatum, a brain structure that plays an important role in decisions, movements, and motivations.

“Anxiety (and its co-conspirator ‘worry’) is an active, energy consuming process,” the study’s lead author, M. Justin Kim of Dartmouth College, told PsyPost. “You haven’t given up – you are still fighting back, trying to anticipate what might happen tomorrow. The problem of course is that there are an infinite number of ‘what if…’ scenarios you can come up with. For some individuals, the uncertainty of what ‘might happen’ tomorrow, is actually worse than the negative event itself actually happening. These individuals are intolerant of uncertainty.”

“We were interested in how uncertainty and ambiguity of potential future threat contribute to the generation of anxiety and how they might be represented in our brain. In the psychology literature, how we deal with an uncertain future can be quantified as intolerance of uncertainty (IU). As is the case with any other personality characteristic, we all have varying degrees of IU. For example, individuals high in IU display difficulty accepting the possibility of potential negative events in the future. Importantly, psychiatric disorders such as generalized anxiety disorder (GAD) or obsessive-compulsive disorder (OCD), whose symptoms are marked with worrying/obsessing, are commonly associated elevated IU.”

“We noticed that while much of the neuroimaging research on IU has been primarily focused on brain function, brain structural correlates of IU have received little attention so far,” Kim said. “As such, we believed that it was an important endeavor to assess the relationship between IU and the structural properties of the brain, which can be done through the use of magnetic resonance imaging (MRI) techniques.”

Kim and his research team recruited 61 students and gave them a survey to measure their ability to tolerate the uncertainty of future events. These participants then had MRI scans taken of their brains.

“Our data argue that structural alterations of the striatum are linked with normal variations in a dimensional personality characteristic (i.e., IU) that has ties with GAD or OCD, rather than the pathophysiology of these disorders per se,” Kim explained to PsyPost.

There was no evidence that any other brain structure was associated with intolerance of uncertainty.

“Previous studies have observed enlarged striatum in patients with GAD or OCD,” Kim said. “What is new here is that we observed this relationship in psychiatrically healthy individuals – meaning that the relationship between the size of the striatum and IU is relevant to all of us, not just individuals with these disorders. Having a relatively enlarged volume of the striatum may be associated with how intolerant you are when facing an uncertain future, but it does not mean you have GAD or OCD. Whether or not this IU-striatum relationship will be helpful in predicting future onset of the disorders, since all our study participants were relatively young (aged 18-26), remains to be seen.”

Kim acknowledged that his study had some limitations.

“We focused on psychiatrically healthy, young individuals and IU within the normal range. Since the observed IU-striatum relationship was independent of self-reported levels of trait anxiety, a general feeling of anxiousness that is commonly elevated in all anxiety disorders, one important question that needs to be addressed in the future is how might these findings translate into a clinical setting, especially for treating symptoms specific to GAD or OCD (excessive worrying or obsessing about uncertainty, which is linked with extreme levels of IU) – perhaps by targeting the striatum and tracking its volume over the course of treatment.”

The study used a cross-sectional methodology, in contrast to a longitudinal one, so the researchers cannot make inferences about cause and effect.

“In addition, there is still more work to be done to understand the exact mechanisms that would explain how more gray matter in the striatum reflects our behavior. As we learn more about the specific neurochemistry of the striatum, perhaps this will offer a clue for pharmacological interventions that might modulate striatal activity. Finally, in tracking healthy individuals with an enlarged striatum, we might find that measuring the volume of the striatum in young adults could predict those at risk for developing GAD or OCD, which could collectively contribute to a data-driven, brain-based approach on the diagnosis of these psychiatric disorders.”

“The functional relevance of the striatum in the context of IU can be learned from neurophysiological studies, which have demonstrated that the striatum is sensitive to the predictability of reward outcomes during learning tasks and rather than to the reward itself. Given that an important component of IU is a desire for predictability, our findings offer a neuroanatomical link related to our need for predictability – when we feel we know what will happen next, this decreases our baseline levels of anxiety, allowing us to focus and get our work done with less distraction.”

The study, “Intolerance of Uncertainty Predicts Increased Striatal Volume“, was also co-authored by Jin Shin, James Taylor, Alison Mattek, Samantha Chavez, and Paul Whalen. It was published May 15, 2017.