Human perception is changed by traumas in the long run

People with mistreatment experiences in childhood have a changed perception of stimuli later as adults. For example, traumatized people found touch stimuli less reassuring than people without trauma.

Greater social distance and less calm from tactile stimuli are some of the effects

People with mistreatment experiences in childhood have a changed perception of stimuli later as adults, according to new research from the Department of Medical Psychology at the University of Bonn, Germany. Traumatized people found touch stimuli less reassuring than people without trauma. In addition, they kept a greater social distance from unknown persons. The researchers discovered changes in the activation of certain brain areas.

People that were humiliated, beaten or sexually abused in childhood are more likely to suffer from mental illnesses such as depression or anxiety attacks in adulthood than people who were spared these experiences at a young age. Numerous studies show this. But what are the reasons for this increased vulnerability? Do experiences of violence as a child possibly lead to a permanently altered perception of social stimuli? Scientists from the Department of Medical Psychology at the Bonn University Hospital (Germany) and their colleagues from the Ruhr University Bochum (Germany) and Chengdu University (China) have investigated this question.

A total of 120 people were interviewed about their experiences with violence and accompanying illnesses. A total of 92 adults (64 of which were women) were included in the study. The prerequisite was that the participants neither suffered from neurological diseases nor took medication to exclude these influences. The scientists tested sensory perception by stroking the naked skin of the shins with one hand in either a fast or a slower movement. "Touching is of central importance because it influences brain development, gives a feeling for one's own body and acts as a stress regulator," says Dr. Dirk Scheele of the Bonn University Hospital's Department of Medical Psychology.

Nerve fibers are specialized in different stimuli

The main study author Ayline Maier explains that interpersonal contact is mediated in the skin via two different nerve fibers, Aß-fibres, and C-tactile fibers. During the experiments, the test subjects lay in a brain scanner and could not see the person who performed the movements. The hands were covered in cotton gloves to avoid direct skin contact. The functional magnetic resonance tomography recorded the activity of the brain areas. After each measurement, the participants were asked how calming the touches were.

The more pronounced the maltreatment experiences were during childhood, the more strongly two brain regions reacted to rapid touches. One affected brain area was the somatosensory cortex. "This area encodes haptic sensations and is involved in the preparation and initiation of body movements - for example, pulling away the part that was touched," said Maier. The other area was the posterior insular cortex. "In traumatized people, the activity of fast touches in these two areas is considerably increased," said study co-author Scheele summarising the results.

Significantly weaker activation of the hippocampus after trauma

The hippocampus, on the other hand, was much weaker during slow touches when traumatic experiences had been made in childhood. "Specifically, the activity of the hippocampus could reflect how rewarding a touch was in the experiment," explains Maier. In particular, more traumatized participants might find a slow and thus more emotionally charged touch less rewarding.

In addition, social distance was also examined. Participants were asked to approach a person they did not know and to stand still when the distance was just perceived as pleasant. It was significantly greater in more traumatized people - on average by twelve centimeters.

Potential for new therapies

"The results show that the perception and sensory processing of people with traumatic childhood experiences have changed," Scheele sums up. Touching for trauma sufferers is less reassuring than for people without experience of maltreatment. As control studies show, it is not accompanying illnesses such as depression or anxiety attacks that are responsible, but traumatization itself. "However, this result may also open up opportunities for new therapies: Supplementary body-based therapies in a safe environment could make it possible to retrain this processing of stimuli," Maier considers. But this potential needs to be investigated to further detail in following studies.

Ayline Maier, Caroline Gieling, Luca Heinen-Ludwig, Vlad Stefan, Johannes Schultz, Onur Güntürkün, Benjamin Becker, René Hurlemann and Dirk Scheele: Association of Childhood Maltreatment With Interpersonal Distance and Social Touch Preferences in Adulthood, The American Journal of Psychiatry, DOI: 10.1176/appi.ajp.2019.19020212