Young people’s brains cope with stress in a completely different way to adults. This is the conclusion of a study conducted on rats at the University of Haifa. The study found that young rats not only extinguished fear much more rapidly, but that, while in adult rats the plasticity of the prefrontal cortex declined, among young rats a different mechanism actually enhanced plasticity.
“Childhood is a period when the brain and the prefrontal cortex are still developing. Accordingly, there is no reason that the mechanism of action in adults and young people should be the same,” emphasizes Prof. Mouna Maroun, the head of the Sagol Department of Neurobiology at the University of Haifa, who conducted the study.
During exposure to a stressful experience, two cerebral mechanisms enable us to respond efficiently to fear, on the one hand, but also to return to normality once the event ends. During the event, a mechanism located in the amygdala effectively tells us that we are in a frightening situation and must act (fight, escape, freeze on the spot, etc.). After the event, a fear extinction process begins in the prefrontal cortex and effectively returns the body to its routine state. When the latter mechanism fails to function properly, we delay the fear extinction mechanism and continue to experience reactions of fear, leading to symptoms of anxiety and post-trauma.
Until now, conventional wisdom in the field has been that these mechanisms operate in a similar way in young people and adults. However, Professor Maroun explains that she instinctively felt that this assumption was problematic. “It began when I knocked my head while I was in a swimming pool – which provided enough trauma to persuade me not to go back into a swimming pool for a long time. But children who were in the pool and who knocked themselves much more badly than I, didn’t think twice about jumping straight back into the water. When I observed this, I realized that this was something I needed to examine in the laboratory.”
In the current study, undertaken by Professor Maroun and research student Rachel Schayek, the investigators sought to examine whether the cerebral mechanisms described above function in a similar way in young and adult rats. In terms of exposure to trauma and fear extinction, rats are a very close model for human behavior.
In the study, young and adult rats were exposed to a mildly traumatic event. Some were then placed on an elevated platform, creating exposure to stress, while the control groups were not exposed to stress.
After experienced fear, the group of adult rats that were not exposed to stress extinguished the fear more rapidly than the group that was exposed to stress. But among the young rats the picture was completely reversed. After experiencing fear, the young rats exposed to stress actually extinguished the fear more rapidly than the group of young rats not exposed to stress. In other words, exposure to stress among the young rats actually accelerated the return to routine and significantly reduced fear reactions.
After this behavioral examination, the investigators also examined physiological changes to the brain and found a similar pattern. Prefrontal cortex plasticity – the strength of the connection between the synapses (which is indicative of the success of fear extinction) was extremely high among the young rats exposed to stress. Among the adult rats exposed to stress, by contrast, the plasticity level was extremely low, thus further confirming the behavioral observations on enhanced extinction.
According to Professor Maroun, however, the differences were even more significant. In the final stage of the study, the investigators sought to examine the impact of the NMDA receptor (which controls the changes in prefrontal cortex plasticity). It is known that blockage of this receptor in adult rats during exposure to stress helps restore fear extinction. The current study also found that a receptor blocker increased plasticity and accelerated fear extinction in adult rats exposed to stress. However, the drug that blocked the receptor had no impact at all on the young rats – neither in terms of plasticity nor behavior.
“This [last finding] implies that it’s wrong to claim that the mechanisms in adults and young people are identical, and simply operate a little differently. The mechanisms are actually completely different. We can therefore state that while we are familiar with the fear extinction among adults, we still need to work out how the brain works to extinguish fear in young people. The immediate significance of this finding is that we cannot continue treating child trauma victims with the same methods and drugs we use to treat adult victims,” Professor Maroun concluded.