People suffering from anxiety disorder and social phobia lack a proper functioning inhibitory connection in their brain, making them vulnerable to uncontrollable fear, an Austrian study finds.

Researchers at the Medical University of Vienna explain that this “brake” in the brain is necessary to keep the sense of fear at appropriate levels and not spin out of control when a situation doesn’t demand it. Anxiety disorder is one of the most common psychiatric conditions, which has a prevelance rate of 18% and often debilitates sufferers by disruptong sensory perception and psychological well-being. This makes the disorder a costly public health issue with social anxiety disorder (SAD) being one of the most widespread types of clinical anxiety health issue.

The authors of the study used functional magnetic resonance imaging (MRI) to study a circuit in the brain that is important for controlling and regulating emotions. By comparing people with social phobias with healthy subjects, they were able to deduce that a feedback loop in this circuit, which stretches between parts of the brain known as the orbitofrontal cortex (OFC) and amygdala, lacks an inhibitory mechanism that provides negative feedback, which is needed to maintain calmness.

“[W]e observed an important neurophysiologic dysfunction in the emotion regulation circuitry of SAD patients,” write Ronald Sladky and colleagues. “The results of the study…strongly corroborate previous reports of reduced connectivity between the OFC and amygdala in SAD patients by providing first evidence for the actual causal dependencies within this network. Our study thus provides a neurobiological model that may explain the altered appreciation of affective stimuli typically observed in SAD patients.”

Study participants had their brains scanned while they were shown images of faces that conveyed various emotions,  such as laughter, sadness, anger, and happiness.  By applying a new way of analyzing scanning data, which was developed at the University College London, researchers found that the neural activity of SAD patients over-reacted to the pictures in comparison to healthy subjects.

This novel way of looking at MRI data allows for a more nuanced understanding of how brain activity relates to mental disorders. “We have the opportunity not only to localise brain activity and compare it between groups, but we can now also make statements regarding functional connections within the brain,” Sladky noted in a press release. “In psychiatric conditions especially, we can assume that there are not complete failures of these connections going on, but rather imbalances in complex regulatory processes.” 

Source: Sladky R, Höflich A, Küblböck M et al. Disrupted Effective Connectivity Between the Amygdala and Orbitofrontal Cortex in Social Anxiety Disorder During Emotion Discrimination Revealed by Dynamic Causal Modeling for fMRI. Cerebral Cortex. 2013.