The finding could help steer treatment of these disorders away from diagnosis-based therapies to treating their common characteristics.
‘When a person is sensitive to uncertain threat, they can spend the entire day anxious and concerned that something bad could happen to them.’
"Knowing that sensitivity to uncertain threat underlies all of the fear-based anxiety disorders also suggests that drugs that help specifically target this sensitivity could be used or developed to treat these disorders," said senior author on the study K. Luan Phan, Professor at the University of Illinois in Chicago.
"A treatment, or set of treatments, focused on sensitivity to uncertain threat could result in a more impactful and efficient way of treating a variety of anxiety disorders and symptoms," Stephanie Gorka from the University of Illinois College of Medicine, added.
Uncertain threat is unpredictable in its timing, intensity, frequency or duration and elicits a generalised feeling of apprehension and hypervigilance. When a person is sensitive to uncertain threat, they can spend the entire day anxious and concerned that something bad could happen to them, Gorka said.
Panic disorder is one example -- patients are constantly anxious over the fact that they could have a panic attack at any moment, she said. Predictable threat, on the other hand, produces a discreet fight-or-flight response that has a clear trigger and it abates once the threat has resolved.
For the study, the researchers looked at data from participants who underwent a task in two different studies performed at the University of Illinois at Chicago. The two studies, of participants aged 18 to 65, included 25 participants with major depressive disorder; 29 with generalised anxiety disorder; 41 with social anxiety disorder; and 24 with a specific phobia.
Forty one control participants had no current or prior diagnoses of psychopathology. The researchers measured the participants' eye-blink responses to predictable and unpredictable mild electric shocks to the wrist. To elicit blinking during the shock-task, the participants heard short, acoustic tones via headphones.
The study, published in the Journal of Abnormal Psychology, found that participants with social anxiety disorder or a specific phobia blinked much more strongly during the unpredictable shocks, when compared to participants without a mental health diagnosis.