Researchers Propose Fear and Anxiety Are Generated by Separate Brain Circuits

Daniel S. Pine, M.D., of the National Institute of Mental Health, expert on anxiety
Daniel S. Pine, M.D.

Fear and anxiety are often described as primal responses to danger, with their emotional and physiological components triggered by a single fear circuit in the brain. But in the September 9 issue of the American Journal of Psychiatry, two neuroscientists argue that the brain circuits generating the feelings of fear differ from those triggering the body’s physical responses to threats. The researchers propose that an oversimplified model of the brain’s fear circuitry has impeded progress in finding effective treatments for anxiety disorders.

In their article, Daniel S. Pine, M.D., a 2000 NARSAD Independent Investigator at the National Institute of Mental Health, winner of the 2011 Ruane Prize, and a member of Foundation Scientific Council, and New York University neuroscientist Dr. Joseph LeDoux, a member of the National Academy of Science and author of the 2015 book Anxious, suggest a new approach.

They argue that a “survival circuit” in the brain regulates rapidly-deployed defensive responses, such as the accelerated heart rate and tensed muscles associated with a “fight-or-flight” response. Fearful feelings, in contrast, arise from a more slowly-deployed circuit. While there are interactions between the two circuits, their effects are distinct.

Conscious feelings of fear and anxiety arise from different circuits than those that control flight-or-fight responses Tweet >

Distinguishing the unique effects of these two circuits has major implications for finding better treatments, Drs. Pine and LeDoux say.

Animal studies have significantly advanced scientists’ understanding of the brain circuits that control rapid responses to threats. The new findings may help researchers discover better ways to control one set of overactive defense responses, like hypervigilance and excessive avoidance. These responses might lead to an overly aroused, hypervigilant state in patients.

But rapidly-deployed defensive circuits may be distinct from more slowly deployed circuits that underlie fearful feelings, Drs. Pine and LeDoux propose. If so, they say, animal studies may fail to explain key aspects of brain function related to distress. Such feelings lead many people with anxiety disorders to seek psychiatric help.

The scientists note that medications that reduce problems in rapidly-deployed circuits and their associated defensive behaviors in animals are not designed to alleviate patients’ subjective feelings. They acknowledge that such medications may be useful in controlling some symptoms. But the expectation that they should also frequently reduce anxious feelings is, the authors argue, misguided.

These dual systems, the authors say, suggest strategies for better use of available treatments and hypotheses for finding new ones. Since our ability to understand the brain is only as good as our current theories, the authors say, their approach offers a new way forward for how we think about and treat problems related to fear and anxiety.

TAKEAWAY: Behavioral and physiological responses to perceived threats may be triggered by brain circuits different than those that generate fearful feelings. Distinguishing between these two systems could help neuroscientists and clinicians find more effective treatments for anxiety disorders.