In posttraumatic stress disorder (PTSD) is an abnormal physiological reaction may occur when exposed to not only trigger but also any other emotional stimulus, in particular — that causes fear or joy. This British scientists have found: they measured how the participants of their experiment changing the diameter of the pupils (the signal on the autonomic nervous system) when observing different emotional stimuli. When you see the pictures of the pupil in volunteers with PTSD tapers less, and during observation of emotional pictures was more enlarged. A study published in Biological Psychology.
It is believed that the stress response in people with PTSD can be associated with their trauma stimuli: for example, sudden loud sounds can sound like gunshots and scare people who got the disorder as a result of participation in combat. This assumption, however, is largely based on the fact that in most studies the reaction are checking a known-disturbing stimuli.
It is obvious that any mental disorder (especially reactive such as PTSD) can change the reaction to all emotional stimuli. To recognize this change may be not so simple: again, if we are talking about PTSD, the reaction to emotional stimuli unrelated to trauma, may appear not as bright as the reaction to the trigger.
And yet, this change can register — for example, through the assessment of physiological parameters. As a token Robert Snowden (Robert Snowden) from Cardiff University and his colleagues decided to use the change of pupil size. This process is the autonomic nervous system: it is the sympathetic part is responsible for dilator (muscle which dilates the pupil), and the parasympathetic part of the sphincter (he pupil constricts). Since the sympathetic nervous system is responsible for the stress response of the organism, and parasympathetic — for homeostasis, the change in the pupil diameter will actually signal the body’s response to the stressor. Accordingly, the expansion or contraction of the pupil will be able to point out the anomalous third-party incentives that are not related to stressors.
To test this hypothesis, scientists conducted an experiment an experiment involving 20 volunteers diagnosed with PTSD, 28 people who have had a traumatic experience, but who have not been diagnosed with PTSD and 17 control group participants. Participants were shown images designed to elicit different emotions (sadness, happiness and fear), and the changes in their pupils watched with pupillometry. No picture was not associated with injuries of the participants.
The initial pupil size did not correlate with the diagnosis of the participant: both participants with PTSD and control group, and injured volunteers without symptoms of the disorder under the same lighting before the start of the experiment the diameter of the pupils was about the same. Immediately after the presentation of the stimulus (i.e., images) pupils narrowed in all participants, but participants with PTSD contraction was less marked (p < 0.001), which indicates broken the parasympathetic nervous system. As for the picture stimuli, emotional pictures, in fact, expanded pupils of all participants, but participants with PTSD during the observation of fearful and happy pictures pupils dilate stronger (p = 0.003) than the other participants; with a sad picture like this ever happened.
The authors concluded that the abnormal response of the autonomic nervous system (inhibition of the parasympathetic system and activation of the sympathetic system) while PTSD is characterized not only for triggers associated with the trauma, but for all stimuli that can evoke strong emotions like fear or joy.
In General, the change of pupil size is a basic physiological response to a change of lighting: in contact with the retina to bright light, the pupil narrows quickly, and the darkening — gradually expanding. However, as found out by scientists last fall, the external stimulation is not required: you can just think about the bright or dark object.