Illuminating How The Brain Beats Trauma

Scientists have unmasked the neural circuit that underlies psychotherapy for sustainably reducing fear.

AsianScientist (Feb. 25, 2019) – In a study published in Nature, a team of scientists in South Korea has identified how a region of the brain called the superior colliculus is engaged to dampen the fear response in mice.

Suppose you are visually tracking a light swinging side to side. Your attention is naturally diverted to that movement, distracting your mind from what was happening before. This alternating bilateral sensory stimulation (ABS) is thought to support the neural integration of new perspectives and the healing of negatively charged memories. In eye movement desensitization and reprocessing treatment, patients are instructed to recall a traumatic memory while receiving ABS.

Although ABS has been recognized for its long-lasting healing effects, its underlying neural basis has remained unclear. Because of the lack of scientific explanations, many psychiatric doctors shun this form of therapy, although it is listed in many psychotherapy manuals.

In the present study, researchers from the Center for Cognition and Sociality of the Institute for Basic Science (IBS), South Korea, identified the brain pathway upon which ABS acts to reduce fear. They examined whether ABS treatment prevents the return of fear in mice. To form a fear memory, the researchers first subjected mice to a sound while also giving them a mild foot shock, thus training the mice to associate the sound with a painful experience.

After conditioning, the mice were repeatedly exposed to the anxiety-producing sound, but now without the electric shocks, until they no longer found the sound to be stressful. This is known as fear extinction therapy. While initially effective, subjects receiving fear extinction therapy often experience relapses and the return of their fear response. By coupling fear extinction therapy with ABS, however, the researchers were able to prolong fear reduction in mice.

The researchers went on to analyze the brains of mice receiving ABS-paired therapy and found enhanced neuronal activities in the superior colliculus and the mediodorsal thalamic nucleus, a brain region that receives inputs from the superior colliculus. They wondered if this pathway might be responsible for persistent fear reduction.

Using optogenetic methods where a laser is used to modify brain signaling, the researchers were able to block the superior colliculus-mediodorsal thalamic nucleus pathway in mice and cause the fear response to return. Conversely, by using a different laser to stimulate the superior colliculus-mediodorsal thalamic nucleus pathway, they were able to prevent fear relapse.

“By shedding light on the underlying brain circuits of ABS pairing [and its] powerful effects to reduce fear, this study [could one day help] patients suffering from post-traumatic stress disorder,” said Professor Shin Hee-Sup of IBS, a corresponding author of the study.

The article can be found at: Baek et al. (2019) Neural Circuits Underlying a Psychotherapeutic Regimen for Fear Disorders.


Source: Institute for Basic Science; Photo: Shutterstock.
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