Adults who were traumatized as children may be more likely to keep a greater physical distance between themselves and strangers, and may also find touch stimuli less comforting than people without a history of trauma, according to a team of researchers from Bonn University Hospital (UKB) and Ruhr University Bochum in Germany.
Research has shown that people who have been humiliated, beaten or sexually abused in childhood are more likely to suffer from mental illnesses such as depression or anxiety attacks in adulthood than those without a history of abuse.
But according to controlled analyses, these mental disorders are not responsible for the stronger aversion to touch and closeness — but rather the traumatization itself.
The findings, published in the American Journal of Psychiatry, suggest that experiences of violence as a child may lead to a permanently changed perception of social stimuli.
The study involved 92 adults (64 women) who were interviewed about their experiences with violence and accompanying illnesses.
The researchers tested sensory perception by stroking the bare skin of the shins with one hand with either a fast or a slower movement.
“Touch is of central importance because it influences brain development, provides a feeling for one’s own body and serves as a stress regulator,” said Dr. Dirk Scheele of the UKB’s Division of Medical Psychology.
Interpersonal contact is mediated via two different nerve fibers in the skin: Aß fibers transmit sensory information and respond primarily to faster touches, while C tactile fibers transmit emotional well-being and are activated primarily by slow touches, said lead author and doctoral student Ayline Maier.
The participants lay in the brain scanner during the experiments and could not see the experimenter who performed the movements. His hands were in cotton gloves to avoid direct skin contact. The functional magnetic resonance imaging system recorded the activity of the brain areas. After each measurement, the subjects were asked how comforting the touches were.
The more pronounced the maltreatment experiences during childhood, the more strongly two brain regions reacted to rapid touches. The somatosensory cortex is located in the brain approximately above the ear and registers where a touch occurs.
“This area encodes haptic sensations and is involved in the preparation and initiation of body movement — for example, pulling away the leg that has been touched,” Maier said.
The posterior insula cortex is an area deep in the brain behind the temple that is responsible for all body perceptions such as touch, hunger, thirst and pain.
“In traumatized people, the activity in these two areas in response to rapid touches is significantly increased,” Scheele said.
On the other hand, activation in the hippocampus was much weaker during slow touches in those with a history of abuse. The hippocampus serves the formation of memory and thus also stores negative and positive associations of stimuli.
“Specifically, the activity of the hippocampus could reflect how rewarding a touch was in the experiment,” said Maier. More traumatized participants might find a slow and thus more emotionally charged touch less pleasant.
The researchers also investigated social distance. The participants were asked to walk up to a person they did not know and to stop when the distance was just about perceived as pleasant. It was significantly larger in more severely traumatized people — on average by twelve centimeters.
“The results show that the perception and sensory processing of people with traumatic childhood experiences have changed,” Scheele said, summarizing the results. Touching is less comforting in those with a trauma history compared to those without maltreatment experience.
Maier said, “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 stimulus processing.” However, this potential would first have to be investigated in more detail in further studies.
Source: University of Bonn