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Effect of EMDR even proven in mice in experiments

19 April 2021

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

This form of therapy works with so-called extinction learning ("extinction"). Here, a new (fear-)inhibiting reaction is learned through which the learned fear reaction is to be suppressed. Based on the assumptions of EMDR that 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 heard 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 go into shock paralysis. The researchers now asked themselves whether a moving light leads to a better unlearning of the fear reaction when the acoustic stimulus is heard or to learning 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 is supposed to reduce the fear reaction. In fact, the fear reaction in the mice decreases faster and reaches a lower level under the condition "extinction with simultaneous EMDR" than under "extinction alone". In order to check whether there is a correlation between the moving stimulation and the simultaneity of the stimulation with the sound, three control conditions (LEDs light up continuously, LEDs flash or LEDs move back and forth) were used. It was shown that the moving LEDs with simultaneous presentation of the sound produced the effect of reduced fear response. EMDR can therefore also be performed on mice and has a much stronger effect than the use of extinction alone. This means that "EMDR" helps mice to unlearn fear significantly better than behavioural therapy 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. The mechanisms located in the deeper layers of the superior colliculus were investigated, which lead to an accelerated reduction of the fear reaction through EMDR. In another mouse experiment, again with the stimuli used - sound and light - studies found that the back-and-forth movement of the visual stimulus activated the most neurons and thus reduced the fear response more quickly. In the "extinction plus EMDR" condition, 63.3% of neurons were activated, compared to only 33.7% in the "extinction" condition. The researchers deduced from this the effect of EMDR through increased activation of the superior colliculus.

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

On EMDR treatment