Very young found to process fear memories in ...( WASHINGTON DC Feb. 5 2008 Very youn...),Health

WASHINGTON, DC Feb. 5, 2008 Very young brains process memories of fear differently than more mature ones, new research indicates. The findings appear in the Feb. 6 issue of The Journal of Neuroscience. The work significantly advances scientific understanding of when and how fear is stored and unlearned, and introduces new thinking on the implications of fear experience early in life.

This important paper raises questions that are the tip of the iceberg related to the very complex series of events that occur as we learn to fear something. In the real world, we become fearful, extinguish that fear, reacquire it at another time, and then conquer it yet again, says John Krystal, MD, of Yale University and director of the clinical neuroscience division of the VA National Center for Post-Traumatic Stress Disorder. Typically, we think about long-term, negative impact of fear learning, such as lifelong problems with anxiety. But this work highlights an avenue for adapting to early stresses that apparently can occur only early in life: to erase a learned fear from memory. Krystal was not affiliated with the research.

Study co-authors Jee Hyun Kim and Rick Richardson, PhD, of the University of New South Wales in Sydney, homed in on the amygdala, using anesthesia to temporarily inactivate it and therefore isolate its role. The amygdala is critical for emotional learning and plays a central role in dulling the memory of a fear.

Kim and Richardson trained rats that were 16 and 23 days oldthe human equivalent of children and budding adolescentsto 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,
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