Thesis defense Mahur Hashemi (Donders series 501)

09 April 2021

Promotor: Prof. dr. K. Roelofs
Co-Promotor: Dr. F. Klumpers

Exploring defensive freeze-fight reactions in humans: from adaptive defence to stress vulnerability

Acute threat triggers primary defensive reactions such as freeze-fight-flight. Reports of disasters show that individuals vary in the way they respond to threatening, traumatic events. While some switch into goal-directed actions, others fight-flight or freeze. Similarly, five to twenty percent of individuals develop post-traumatic stress disorder (PTSD) after experiencing a traumatic event. At this moment, the role of defensive reactions in the different stages of PTSD pre- and post-trauma remains largely unknown in humans. In a large-scale, prospective study in young police officers in training, this thesis reveals the underlying psychophysiological mechanisms of defensive reactions and the role of these reactions in the development of stress and trauma symptoms. Results show that an altered pattern of freeze-fight reactions predicts stress vulnerability. Before being exposed to trauma, increased postural freezing to acute threat is associated with vulnerability markers of anxiety and stress. Moreover, increased activations in the dorsal amygdala during defensive reactions and before trauma exposure predict the development of trauma symptoms. This knowledge provides a basis for further research into risk markers for stress vulnerability and potentially also for the development of early intervention programs to reduce harm for risk groups.