It might be important to explain what is meant by an "abreaction." In EMDR, the model states that the perceptions experienced at the time of the event can get locked in the brain in state-dependent form. That is, they can contain not only the image, thoughts and sounds, but the emotions and sensations experienced at the time of the event. When the trauma is targeted and reprocessed with EMDR the client will experience it at some level. They may feel only a shadow of the original perceptions, or they can experience it at a high level of disturbance. If there is a high level of disurbance we call it an abreaction. It does not mean that the client is lost in the event or writhing on the floor. It merely means that the client's disturbance is at approximately an 8 or above on a 0-10 scale.
There is no research that I know of on this aspect of EMDR. However, anecdotal reports from Level II participants indicate that approximately 15% of the clinical population will experience a severe abreaction. As with any other subjective experience, the client is rapidly lead through the processing of the material. With the use of the cognitive interweave, a client can go from terror through fear through disgust/anger through acceptance/joy in less than twenty minutes. The rapid treatment effects make it possible to view the transmutation of emotional states and given present interest in affect theory, it could make a very useful research project.