Chinese scientists discovered this after separating young mice from their mothers in front of their littermates. The ‘transmissible fear’ that they subsequently observed in the littermates of the traumatized mice also occurs in humans, the researchers believe.
We know that children who experience traumatic events early in life are more likely to develop neuropsychiatric diseases such as anxiety later in life. However, it was not yet known what it does to someone to witness such a traumatic experience, even though this also happens regularly. Researchers from the Guangzhou University therefore decided to investigate whether other people’s fear can be transferable and can also have an impact on the brain and behavior later in life.
To do that, Jiang and colleagues set up a heartbreaking animal experiment, separating mice from their mothers. That event, also called maternal separation, is one of the biggest stressors in early life and is therefore used to study stress in early life. “In this way you not only measure the transferability of acute stress, such as physical pain stimuli, but also that of psychological stress,” says researcher Li Yang. When the mice reached adolescence, the scientists examined the brains and behavior of both the mouse that was separated from its mother and the littermates that saw this happen.
Fear testing
To do this, the mice had to perform an open field test and a plus-maze test, both methods for measuring anxiety in rodents. In the open field test, the mouse is placed in a square and the researchers measure, among other things, how long the mouse spends in the center. The plus maze test consists of a construction in a plus shape, where two of the four arms have walls around them and the other two are open. Because open spaces are more dangerous for prey animals such as mice, how much time they spend in those places can say something about how safe they feel. What turned out was that both the mice that had been separated from their mother and the brothers and sisters who saw it happen walked for less time and distance in the open field compared to the control mice. They also spent less time in the open arms of the plus.
Brain connections
In addition to behavior, the scientists also looked at specific brain connections in the anterior ‘cingulate cortex’: a brain region that plays an important role in physical and social pain, both in rodents and humans. It showed that the mice that were separated from their mothers had difficulty with the balance between inhibiting and activating brain cells in that area. The littermates who witnessed the separation between mother and child were even more affected. Yang: “That shows that these parts of the brain are not only involved in fear due to personal experiences, but also in transferable fear.”
Mens
Although research into transmissible anxiety has so far only been conducted in mice, researchers believe the process works similarly in humans. “Taking over emotions occurs in many social mammals,” says Yang, “and the other animal does not have to be physically present.” In rodents, for example, smell plays an important role in conveying fear. To smell the other mouse’s odor of fear, you do not have to see the event with your own eyes, says Yang. This also applies to people – although it may require more than just smell, the researcher admits. But you also see this effect in people. “If you hear that someone is suffering because of a traumatic event, it can really bother you. Actually, that’s just a form of empathy.” The question is to what extent that fear lingers. “Usually those emotions of compassion don’t last very long.”
The research may contribute to new treatment methods for anxiety in the future. Yang: “Our research has found very specific brain cells in the anterior ‘cingulate cortex’ that are involved in the transmission of fear. It is therefore certainly interesting to look at those areas for the treatment of transferred anxiety.”
2023-10-21 17:19:43
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