Young people’s brains cope with stress and fear in a completely different way to adults, challenging the assumption that brains of humans of all ages react similarly to fear. Whether it’s hesitancy to ride a roller coaster or the tendency to drive in the slow lane, the study’s findings may finally explain why people tend to become more cautious as they age.
A University of Haifa study conducted on rats found that young rats were able to eliminate fear in the brain more rapidly than adult rats. Adults, on the other hand, continue to feel fear, even after the fearful event has passed.
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Until now, conventional wisdom in the field has been that these mechanisms operate in a similar way in young people and adults. However, Prof. Maroun, Prof. Mouna Maroun, head of the Sagol Department of Neurobiology, who conducted the study, explains that she instinctively felt that this assumption was problematic.
“It all began when I was knocked my head while I was in a swimming pool – a mild form of trauma, but enough 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 did didn’t think twice about jumping straight back into the water. When I saw this, I realized that this was something I needed to examine in the laboratory.”
According to the study, this increased fear with age is related to the plasticity or flexibility of the prefrontal cortex of the brain, the area responsible for complex cognitive behavior. “Childhood is a period when the brain and the prefrontal cortex are still developing. So the mechanism of action in adults and young people [is not] the same,” emphasizes Prof. Maroun.
Decoding the mechanism of fear extinction
During exposure to a scary or 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 amygdale, an almond-shaped structure in the brain, effectively tells us that we are in a frightening situation and must act (fight or flight). 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 continue to experience reactions of fear while we no longer need it, leading to symptoms of anxiety and post-trauma. According to the study, this explains why adults are usually more cautious in comparison to children regarding extreme or challenging activities, because their brains delay the fear extinction mechanism.
The young and the fearless
In the study, young (postweanling) and adult rats were exposed to a mild traumatic event. Some of them were then placed on an elevated platform, creating exposure to stress, while the control groups were not exposed to stress.
The findings showed that the adult animals reacted as expected: strong fear responses were seen by comparison to the rats that were not exposed to trauma. The group that was not exposed to stress extinguished fear more rapidly than the group that was exposed to stress. But among the young rats the picture was completely reversed. The fear reactions of the rats exposed to trauma were much lower, and the fear extinction time was much shorter, than among the adult rats. Moreover, the young rats exposed to stress actually extinguished fear more rapidly than their peers that were 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.
Exposing the need for age-tailored trauma treatments
Following 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 correlates with the success of extinction – in the area responsible for 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, showing damage to plasticity by comparison to the control group, 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. This receptor controls the changes in prefrontal cortex plasticity and is responsible for the successful acquisition of fear extinction. It is known that blockage of this receptor in adult rats during exposure to stress helps restore fear extinction to the level in the control group. 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 implies that it’s wrong to claim that the mechanism in adults and young people is identical, and simply operates a little differently. The mechanism is actually completely different. We can therefore state that we are familiar with the fear extinction among adults, but that 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 really cannot continue treating child trauma victims with the same methods and drugs we use to treat adult victims,” Prof. Maroun concluded.