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Suppose you visually follow a moving light swaying from one side to the other. Your attention is naturally directed to this movement, and what you had in mind before is set aside. This alternating bilateral sensory stimulation (ABS), as part of the desensitization and reprocessing of eye movements (EMDR), is supposed to support the neural integration of new perspectives and the healing of negatively charged memories. Although this treatment has been recognized for its long-term healing effects, the underlying neural base is not yet clear. Due to the lack of scientific explanations, many psychiatrists avoid this form of therapy, although it appears in many psychotherapy textbooks. Researchers at the Center for Cognition and Sociality at the Institute of Basic Sciences (IBS) have identified the brain pathway in which ABS acts to induce a persistent reduction in fear.
In EMDR, patients are invited to recall a traumatic memory when they receive ABS. Since these visual-attentional processes are commonly used in patients with post-traumatic stress disorder (PTSD), the researchers hypothesized that a region of the brain responsible for the movement of the eye and the attention – the upper colliculus – could be involved in fear. reducing effect of ABS.
The researchers first examined whether the treatment badociated with ABS prevents the return of fear. To form a memory of fear in mice, the researchers first subjected them to sound while applying a slight shock to the foot, causing them to badociate the sound to a painful experience. We have seen fear in the mice freeze at the place. The mice were then repeatedly exposed to the sound that caused the anxiety, but now without electric shock, until they found that the sound was no longer stressful. This is known as extinction therapy for fear. This conventional exposure therapy in humans is often followed by a severe relapse of symptoms. To test the effects of visual simulation on fear responses in mice, the researchers placed the mice in a cylinder-shaped container with LEDs installed on the wall.
The conventional fear reduction procedure attenuated fear (frost) reactions with repeated exposure to sound where foot shocks had occurred before. However, fear responses often come back when the sound is presented a week later at the same location or in a new location. In contrast, visual stimulation (light in motion) with sound, which is the ABS coupling, has resulted in a persistent reduction of fear without significant return, thus confirming the powerful effect of ABS coupling to reduce fear.
The researchers found improved neuronal activities in the SC and in the thalamic mediodorsal (MD) nucleus that receives inputs from the SC. They wondered if this SC-MD path could be the path taken by the ABS, which would have the effect of reducing fear. "To confirm this causal link, we have blocked the SC-MD pathway when pairing ABS using a yellow laser light," said Jinhee Baek, one of the first authors of the report. study. This modulation blocked the effect of ABS and brought a significant return of fear. Conversely, when blue laser light stimulated neuronal activities in the SC-MD pathway, mice exhibited significantly reduced freezing without relapse of fear. Using these experiments, the researchers determined that the SC-MD pathway was essential to prevent the return of fear.
Mr. Baek said, "We then wondered what mechanism suppressed the expression of fear." The researchers examined the basolateral tonsil (BLA), an area of the brain that controls the expression of fear and stores the memory of fear. ABS coupling inhibits neurons expressing fear in BLA. Using yellow laser light, the researchers blocked the MD-BLA pathway. Blocking induces excitatory activities and also delays inhibitory responses in the BLA. "This study discovered a new function of MD neurons in suppressing BLA's fear responses," says Baek.
Studies using animal models have focused on direct approaches, removing the original fear memory with chemicals that alter synapses or neurons, making these approaches inappropriate for clinical applications. In addition, current psychotherapeutic methods have been used in humans without understanding how these treatments help to reduce traumatic symptoms. The study discovered neural circuits underlying the psychotherapeutic method. Upper colliculus (SC), known only to be responsible for eye movement and attention, was previously not considered involved in modulating responses learned through fear. Notably, the neural pathway reported in this study induces a more stable inhibition of fear without a significant return of responses to fear. "By highlighting the powerful effects of ABS coupling on the brain of the underlying brain circuits to reduce fear, this study can comfortably rebadure its effects reducing fear in patients with PTSD," says Dr. Hee-Sup Shin, one of the corresponding authors of the study.
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