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Effect of EMDR proven even in mice in experiments

April 19, 2021

The mechanism of action of the therapy form EMDR (Eye Movement Desensitization and Reprocessing) was presented within a mouse model of fear conditioning. The aim is to treat post-traumatic stress reaction (PTSD) by unlearning fear using alternating bilateral stimulation.

This form of therapy works with so-called extinction learning ("extinction"). Here, a new (fear) inhibitory reaction is learned, through which the learned fear reaction is to be suppressed. Based on the assumptions of EMDR that an alternating stimulation of different stimuli (moving the eyes back and forth, alternating touches, lights or even sounds) is helpful in processing traumatic experiences, this was investigated in an experiment with mice. This is preceded by Ivan Pavlov's well-known animal model of classical conditioning. South Korean neuroscientists constructed a special cage in which mice were first given a painful, electrical stimulus (unconditioned stimulus) via the floor of the cage. At the same time, an acoustic stimulus (conditioned stimulus) was sounded through a loudspeaker, so that the two stimuli were associated with each other by the mice. After successful conditioning, the acoustic stimulus alone caused the mice to react in the same way as the painful electrical stimulus - namely, to fall into a state of shock paralysis. The researchers now asked themselves whether a moving light would lead to a better unlearning of the fear reaction when the acoustic stimulus was heard, or to the learning of the new reaction of not being afraid.

For the application of EMDR in mice, the animal sits in a cylindrical cage, which is surrounded by LEDs. When the acoustic stimulus is presented again, the back and forth movement of the light simultaneously directs the animal's attention back and forth, which should reduce the fear reaction. In fact, the fear response in the mice decreases faster and reaches a lower level under the "extinction with simultaneous EMDR" condition than under "extinction" alone. To verify whether there is a relationship between the moving stimulation as well as the simultaneity of the stimulation with the tone, three control conditions (LEDs lit continuously, LEDs flashing, or LEDs moving back and forth) were used. It was shown that the moving LEDs with simultaneous presentation of the tone produced the effect of reduced fear response. So EMDR can be done in mice and has a much stronger effect than using extinction alone. That is, "EMDR" is significantly better at helping mice unlearn fear than behavioral interventions alone.

But what anatomical mechanisms underlie the effectiveness of EMDR? Since the 1970s, the superior colliculus, one of the best-studied structures of the midbrain, has been associated with eye movements and focusing on an object. Mechanisms located in the deeper layers of the superior colliculus were investigated, which lead to an accelerated reduction of the fear response through EMDR. In doing so, studies in another mouse experiment, again with the stimuli used- sound and light, found that the back-and-forth movement of the visual stimulus activated the most neurons, resulting in a faster reduction of the fear response. In the extinction plus EMDR condition, 63.3% of neurons were activated, compared to only 33.7% in the extinction condition. From this, the researchers deduced the effect of EMDR was through increased activation of the superior colliculus.

Here is the link to the original article: Spitzer M. Neurology 2019; 38: 231-239.

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