Extinguishing fear is different in the young brain
February 7th 2008 20:53
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Researchers trained rats that were 16 and 23 days old—the human equivalent of children and adolescents—to associate a specific sound with a mild shock to the foot.
After subsequent training, when the sound was not followed by a shock, the animals’ fearful reaction to hearing the sound faded.
Technically, this is known as “extinction,” and depended on the function of the amygdala.
In a second round of training, the researchers reintroduced the fear and tried to re-extinguish it.
This time around, they found, only the older rats were able to do so without the amygdala.
The researchers concluded that the age at which the initial extinction training occurred was critical to whether or not the rats’ fear faded the second time independently of the amygdala.
The authors suggest that in the very young, it is primarily the amygdala that extinguishes fearful memories, but that mechanisms independent of the amygdala develop later.
This raises the possibility that fears unlearned at an early enough age are, in fact, erased. As brains develop, however, and related structures near the amygdala mature, these structures take on a greater role.
Thus, fear in adolescence and later in life may not be erased, but instead be, for example, inhibited by a process of overlaying neutral memories on top of the initial fear reaction. The initial memory could still exist and be called on again.
“Extinction in the young brain might forever erase early traumatic learning—but accepting this hypothesis will have to wait for more research,” says Mark Bouton, PhD, of the University of Vermont, who did not participate in the research.
“What might change as the brain develops is where and how fear learning and extinction are stored and how they can be retrieved.”
Information from the Journal of Neuroscience and reported in RedOrbit.
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